Welcome

This special eBook contains a compilation of articles on the DigiLite project.

Please visit http://www.g8ajn.tv/dlindex.html for the latest information and updates.

DigiLite System Overview

by G4EWJ (edited by G8AJN)

DigiLite is a system designed by radio amateurs to provide a lower cost method of home building a digital modulator for transmitting live digital TV pictures (DATV). It is a derivative of the Poor Man's DATV System which many amateurs have contributed to over several years. The system has 6 main parts:

- A Windows PC with a video capture card that uses an MPEG-2 compression chip.

- A recording program on the PC to save the data from the capture card onto hard disk.

- A program running on the PC to read the recorded data from hard disk, convert it to a form suitable for transmission and send it to a serialiser.

- A serialiser, which is a device that connects between a PC USB port and a modulator.

- A QPSK modulator.

- A program to configure the transmission parameters.

DigiLite System Outline Details

A Windows PC with a video capture card that uses an MPEG-2 compression chip. The current project assumes a WinTV PVR card. A recording program on the PC (either WINTV v 7 or GBPVR v1.4.7 )to save the data from the capture card onto hard disk.

A program running on the PC to read the recorded data from hard disk, convert it to a form suitable for transmission and send it to a serialiser. A serialiser, which is a device that connects between a PC USB port and a QPSK modulator. A program to configure the transmission parameters.

If an older PC is available, which can be dedicated to DigiLite, this is ideal. A single core 1.8GHz processor with USB2.0 should be sufficient on a 'quiet' system. On a non-dedicated PC, if Windows gets busy doing other things, the conversion program may not get all the processing time it needs and that can cause an occasional glitch in transmission. The more powerful the PC, the less chance there is of this happening.

Recording program

DigiLite has been designed to use the Hauppauge PVRx50 PCI video capture cards. There is also a Hauppauge PVR USB2 external device that can be used with laptops. Other cards are being evaluated, but they need to do the mpeg2 encoding in hardware (in an IC not in software).There are often WinTV cards cards available cheaply on Ebay etc.It should be possible to get a card and disk (a disk is needed to download WinTV v 6 free). If you dont get a disk you will need any version of an Original Hauppage Install disk in the PC to get a free download of the WinTV 6 programme.

If you cannot get WinTV you can use GB-PVR.

VGBPVR is a free PVR (personal video recorder) program. Version 1.4.7 has been used sucessfully.Later version may not work. GBPVR requires a certain standard of video graphics card to run, even if you do not actually want to watch the video on that PC. Older graphics card may have problems. More card details on hardware pages.

Conversion program

DigiLite Transmit is the program that reads the recorded data from hard disk immediately it has been written.

The data is in Program Stream format, which is very similar to the format used on DVDs. The video and audio are extracted and converted into DVB-S transport stream format, which is the format used by European broadcasters to deliver standard definition programs via satellite. This means that a cheap FTA (free to air) satellite box may be used to receive the transmission. Other data is placed in the transport stream such as date and time, channel name, program name and Electronic Program Guide info. The transport stream data is sent to the serialiser via a USB2 port.

Serialiser

This is the device that connects to a high speed (480Mbps) USB 2.0 port and accepts the transport stream data from the PC. Two bits at a time (a symbol) are sent to the modulator at the symbol rate. The serialiser may optionally apply the FEC (aka Viterbi) forward error correction processing to the transport stream data, or this can be done on the PC. Doing the FEC on the serialiser is prefferred as it reduces the data rate over the USB connection. The serialiser has a second communication channel which is used to receive control information from DigiLite Transmit to set the required symbol rate and FEC.

The serialiser can also be put into one of several test modes, to help set up the modulator. The serialiser has been used successfully at symbol rates between 1250k and 6250k. Several symbol rates are pre-programmed into the system.

The serialiser has an SD card socket for playing pre-recorded transport stream files. This function is still in development and is not available in the initial release. The serialiser CPU chip dsPIC333 will need to be re-programmed to add new functions such as this.

Modulator

QPSK stands for Quadrature Phase Shift Keying. The modulator must be provided with a signal source at the required transmission frequency. It filters the two digital signals (I and Q) from the serialiser and produces an output at the transmission frequency which can then be amplified and transmitted. The type of filtering used is known as 'Nyquist'.

Configuration

DigiLite Config is the program that is used to set the symbol rate and FEC and also the channel name and program details.Settings are stored in the Windows registry, which DigiLite Transmit monitors continually to look for any changes in transmission parameters.DigiLite originally began life as the 'Poor Mans Digital encoder'. Credits must go to those with the original concept.(including F4DAY and F1HPR ). Brian G4EWJ has worked on the software and developed the serialiser and USB version. Using the MPEG2 encoder chip on the WIN TV capture card with a PVR program to record on to a PC's hard drive whilst simultaneously reading from the file to create a serial USB stream.

This goes to the serialiser board where the stream is buffered and extra code is added to the packets before being sent to an IQ modulator as a Transport Stream. The modulator uses a local oscillator set to the required output frequency,e.g. 1249MHz. Rob(M0DTS) worked on getting the PC to serialiser and modulator hardware running up to the required 4Ms/s and using the more convenient USB input. Brian(G4EWJ) worked on the hard drive reading software for the serialiser and USB and moved it from the original Linux software to the current Windows version. Test boards were built by Rob and Malcolm G0UHY to confirm that it can be replicated. Symbol rates were gradually stepped up from 2Ms/s to 4Ms/s and above.

Here is a description of the digital system adapted from the M0DTS website...

A Digital ATV Transmitter is built of 3 main stages, these are: MPEG-2 encoder, multiplexer, Error correction and Convolutional coding, Serialiser, Nyquist filter and then to an IQ modulator.The MPEG-2 encoder takes the analogue Composite video and audio signals in and converts them into a digital signal; it then gets compressed into the standard MPEG-2 format. Currently using a Hardware MPEG-2 encoder, the Hauppauge PVR-150 (or 250/350/500) pci card in the PC.The multiplexer takes the MPEG-2 audio, video and service information and puts them into one single stream called a Transport Stream which is made of 188 byte long packets of data.Software reads the transport stream from the HDD and splits it into separate Audio and Video elementary streams, Service Information tables (PAT, PMT, SDT, EIT etc.) are added also Reed Solomon correction is added into the transport stream.

The serialiser takes in the parallel data stream and converts it to a serial stream in IQ format ready for the modulator. This is done in a microprocessor dsPIC333.The Nyquist filter is a special Low Pass Filter that removes the unwanted sidebands from the I/Q signals and retains the impulse response of the data signal very well, the same as used in the F4DAY system. The filtered IQ outputs are fed into a modulator, using F1HPR's design, an Analog Devices AD8346 IC for this as it directly modulates the LO (Local Oscillator) for the band you are operating on. This makes it very easy to change between different bands by simply supplying a different LO frequency and some minor adjustments of IQ bias and level (and perhaps the Nyquist filter components if using lower symbol rate). The modulator has preset pot's to adjust balance of I/Q level and I/Q voltage bias for canceling out the LO. After that a a MMIC amplifier gets the signal up to a level required for input to an external amplifier to raise the level to that required by the PA. Remember that the bandwidth of the 4000ks/s is roughly 4Mhz, so the power required to cover as well as the 12Mhz analog one does is much lower. This allows you to lower the drive to your PA and thus get into the best linearity that you can without any loss of coverage.

Please visit http://www.g8ajn.tv/dlindex.html for the latest information and updates.

The Digilite Project - Part 1

by Dave Kenward G8AJN

Background

Why should we care about digital ATV? What’s wrong with analogue tv? Actually, not much really. I have to admit to a personal preference for a good analogue signal over a l ow resolution up-scaled digital signal. Perhaps non- HD digital is clean rather than clear, however on a fair comparison the digital signal is vastly more efficient on bandwidth and power. If looking for dx tv, an analogue signal is simpler to find than a digital signal, whilst ploughing through the noise at least as well, digital has numerous different formats that might prevent you decoding the data. But the reality is that we are being squeezed into ever shrinking band spacing. So whilst the analogue has served us well, it does use a large chunk of bandwidth that looks profligate in comparison to a 6MHz digital carrier.

At the Bournemouth Amateur TV Group we have been attempting to get permission for a 23cm atv repeater GB3SQ for four years and took the radical decision to change the application to digital only. So what does this mean for the local repeater users? We are in a location that doesn’t receive the Isle of Wight atv repeater GB3IV very well, but a signal aimed that way will often get in. This means that we had to choose an input channel very carefully to avoid accidentally opening up the GB3IV input. By using digital-only input it will be possible to co-exist. Currently the Bournemouth repeater is on test and will accept analogue or digital inputs until all the locals have converted to digital transmitters.

When we heard of the system that Brian G4EWJ had been working on with others helping with the prototypes and beta testing we asked if it would be ok if we built some digital encoders using his software and serialiser design. Visit M0DTS website (ref 1) to read about the early development history. The first few locally built boards were made and tested by Colin G4KLB and were very impressive, comparing extremely well with the SR Systems boards and the older NDS 3000 tower systems, even at 4Ms/s. Where previously Colin has required about 40W input analogue signal to get a good P5 into the repeater he was getting an unbroken signal in using 5 W. The boards were based on G4EWJ serialiser board and Malcolm G0UHYs design modulator panel (photo below).

Separate boards version of G4EWJ serialiser built by G4KLB

The BATG members decided that this was the way forward and that is when I realised what an important development Brian had achieved and was determined that it should be made available for everyone to build.

He generously agreed to make the software available as freeware and after some consideration the project was renamed DigiLite. My website was selected to host the initial information and to allow contributions to be collected together to make access simpler. The difficulty with websites is that not only are they easy to setup they have a nasty habit of evaporating equally quickly. A decision was made to transfer all this information to the printed form for posterity.

The original project used separate serialiser and modulator boards. My contribution to the information contained in these notes has been to produce a single pcb with all the components for the serialiser and modulator. I claim no technical acumen, I am simply your guide to the system as it exists today. I aim to explain why you are doing something in terms that an analogue ATV-er can understand. There is nothing to fear in digital ATV and with this system you really do not have to become a ‘nerd’ to get started with digital ATV so do take the time to read through this article as it contains important documentation that the designer of the system has provided. The thrill of seeing your own home built transmitter sending digital signals is as real as it was when you first marvelled at getting an analogue colour tv signal on-air.

DigiLite

Every once in a while Amateur tv takes a step forward. From 405 to 625, from mono to colour and now we can move on to the next step, analogue to digital. Up to now anyone wanting to try to transmit digital has probably been discouraged by the cost. The SR Systems boards do an excellent job but are expensive and a home-brew version has been looked for by those wishing to keep the outlay to a reasonable level.

Much of the original development work has come from a group of French amateurs including F4DAY. Whilst the name Poor Mans DATV(ref 2) seemed somewhat demeaning it did set Brian thinking about a solution to the real- time encoding problem.

Probably the biggest problem was the MPEG encoding, or more precisely real- time MPEG encoding. There is already software around that will encode the image into mpeg2 but it will tend to run on a file, convert it , then save it basis. This would create too much of a delay so for our purposes the encoding is done in hardware. The cheapest and easiest way out of this is to utilise the Connexant chip on the old WINTV PVR cards. These cards send a digital stream to the hard drive for use as a Personal Video Recorder. While the recording is in progress another program DigiLite Transmit is reading it immediately it is written on the HDD and sending it to the serialiser for further processing.

The original software was Linux freeware that had been adapted and required a number of different programs running to get the desired mpeg2 data stream which needed to be broken into and then changes like error correction etc. inserted and then re-assembled. By moving the software from Linux to Windows it has enabled a more user-friendly single program to be developed.

In future editions I will take you through the building and setup of the hardware and the installation and setup of the software with a single commercially produced printed circuit board (100mm x 70mm) available with lots of assistance in making the project. Much of this work has been achieved by Brian G4EWJ. Here is his brief guide to the system:

DigiLite System Outline

DigiLite is a system designed by radio amateurs to provide a lower cos method of transmitting live digital TV pictures (DATV). It is a derivative of the “Poor Man’s DATV System” which many amateurs have contributed to over several years.

The system has 6 main parts:

- A Windows PC with a video capture card that uses an MPEG-2 compression chip.

- A recording program on the PC to save the data from the capture card onto hard disk.

- A program running on the PC to read the recorded data from hard disk, convert it to a form suitable for transmission and send it to a serialiser.

- A serialiser, which is a device that connects between a PC USB port and a modulator.

- A QPSK modulator.

- A program to configure the transmission parameters.

Windows PC

If an older PC is available, which can be dedicated to DigiLite, this is ideal. A single core 1.8GHz processor with USB2.0 should be sufficient on a ‘quiet’ system.

On a non-dedicated PC, if Windows gets busy doing other things, the conversion program may not get all the processing time it needs and that can cause an occasional glitch in transmission. The more powerful the PC, the less chance there is of this happening. DigiLite has been designed to use the Hauppauge PVRx50 PCI video capture cards. There is also a Hauppauge PVR USB2 external device that can be used with laptops. Other cards are being evaluated.

Recording program

GBPVR is a free PVR (personal video recorder) program. Version 1.4.7 has been used the most, but it has been superseded by NextPVR, which is still being evaluated. GBPVR requires a certain standard of video graphics card to run, even if you do not actually want to watch the video on that PC. Older graphics cards may have problems. There are other more ‘techy’ ways of recording without using GBPVR in this case. Developments are continuing, to remove the need for a recording program and to interface with the PVR card directly.

Conversion program

DigiLite Transmit is the program that reads the recorded data from hard disk immediately it has been written. The data is in Program Stream format, which is very similar to the format used on DVDs. The video and audio are extracted and converted into DVB-S transport stream format, which is the format used by European broadcasters to deliver standard definition programs via satellite. This means that a cheap FTA (free to air) satellite box may be used to receive the transmission.

Other data is placed in the transport stream such as date and time, channel name, program name and EPG info. The transport stream data is sent to the serialiser via a USB port.

Serialiser

This is the device that connects to a high speed (480Mbps) USB 2.0 port and accepts the transport stream data from the PC. Two bits at a time (a symbol) are sent to the modulator at the symbol rate. The serialiser may optionally apply the FEC (aka Viterbi) forward error correction processing to the transport stream data, or this can be done on the PC. Doing the FEC on the serialiser reduces the data rate over the USB connection.

The serialiser has a second communication channel which is used to receive control information from DigiLite Transmit to set the required symbol rate and FEC. The serialiser can also be put into one of several test modes, to help set up the modulator. The serialiser has been used successfully at symbol rates between 125k and 6250k. Several symbol rates are preprogrammed into the system. Other symbol rates are possible, subject to the limits of the multipliers and dividers in the serialiser CPU phase locked loop. The serialiser has an SD card socket for playing pre- recorded transport stream files. This function is still in development and is not available in the initial release. The serialiser CPU chip will need to be re- programmed to add new functions such as this.

Modulator

QPSK stands for Quadrature Phase Shift Keying. The carrier can be in one of four states with each state defining two bits. The modulator must be provided with a signal source at the required transmission frequency. It filters the two digital signals (I and Q) from the serialiser and produces an output at the transmission frequency which can then be amplified and transmitted. The type of filtering used is known as ‘Nyquist’.

Configuration

DigiLite Config is the program that is used to set the symbol rate and FEC and also the channel name and program details. Settings are stored in the Windows registry, which DigiLite Transmit monitors continually to look for any changes in transmission parameters.

DigiLite Transmit User Guide

DigiLite Transmit is the program that reads the captured video from the PC hard disk in program stream format, converts it to transport stream format and sends it to the serialiser via a USB port.

It reads the transmission parameters stored by DigiLite Config in the Windows registry and displays these. It can detect a change in parameters and then usually needs to restart itself.

Finding a Captured Video File

DigiLite Transmit looks in three places for a growing .MPG file:

1. The folder that DigiLite Transmit resides in;

2. The folder where WinTV recordings are stored;

3. The folder where GBPVR recordings are stored.

WinTV and GBPVR are PVR (personal video recorder) programs.

DigiLite Transmit can determine the recording folder for both of these programs automatically, even if the folder is changed in their configurations. If another PVR program is being used, it should be configured to store recordings in the folder where DigiLite Transmit resides.

Status Messages

‘Waiting for an active recording file’ DigiLite Transmit cannot find a growing .MPG file in the three places where it may look.

‘Cannot open COMxx for DATA / CONTROL’ DigiLite Transmit cannot open the COM port. Check that the USB module is correctly configured and that the COM ports are set correctly in DigiLite Config.

User Control

Hit ESC to stop DigiLite Transmit. Hit R to restart DigiLite Transmit.

Hit SPACE to reset the PCR Lag and Serialiser figures.

Normal Operation

When DigiLite Transmit finds a growing .MPG file, it opens the COM ports to the serialiser and starts normal operation. You should see the counters incrementing on the status line.

Input File

‘Length’ shows the size of the .MPG file which is being recorded. This should increase steadily.

‘Avail’ shows the amount of data at the end of the file which has yet to be processed by DigiLite Transmit. This should be around 100k or less, depending on symbol rate. If greater, try hitting R to restart and see if it improves. If ‘Avail’ keeps increasing, then the video bit rate set in the recording program is probably too high.

PCR Lag

The PCR is the clock which is embedded in the transport stream data. Each frame of video has a time at which it should be displayed, relative to the PCR. The lag figures show the instantaneous and Min / Max values of the relative difference and these vary with the amount of data that each frame contains.

The initial value is set by ‘TS Delay’ in DigiLite Config. Negative numbers mean that some data arrived at the receiver after the time at which it should have been displayed. This may cause a video glitch. This may happen occasionally, but if it happens continually, then the video bit rate in the recording program may be too high. If the ‘Now’ figure reaches one second, then DigiLite Transmit will restart itself. The figures may be reset by hitting SPACE.

Packets Out

‘Total’ is the running count of 204 byte packets sent to the serialiser. Multiply ‘Total’ by 204 and divide by the FEC to determine the total number of bytes transmitted.

‘Pad’ is the number of empty padding packets transmitted. The video bit rate is set to give 95% of the transport stream data and padding packets are inserted to maintain timing in the transport stream as the amount of data per frame goes up and down.

‘Pad%’ is the percentage of packets which are padding. 5% is the target. Anything lower and there is not enough leeway to cope with the varying data rate in the recorded file. Higher values are not a problem, but mean that some transmission bandwidth is being wasted. Low values may mean that the video bit rate in the recording program is too high.

Serialiser

The serialiser communicates back to DigiLite Transmit through the control port. The figures may be reset by hitting SPACE.

Boot

This the number of times that the serialiser has reported a reboot. This should never happen. If it does, it may be that the serialiser CPU is being over- clocked and cannot cope. Select ‘FEC on PC’ in DigiLite Config and see if it stops happening.

Re-sync

There must be no gaps in the transport stream, so if the serialiser runs out of data because of a pause in the data coming in from the USB port, the serialiser reports this back to DigiLite Transmit. This can happen occasionally if Windows gets very busy.

DigiLite Transmit restarts itself and the serialiser waits for its buffer to fill up again. This will cause a video glitch.

DigiLite Config User Guide

DigiLite Config is the program that sets the parameters for the transmission. It communicates through the Windows registry with DigiLite Transmit. Hovering over many fields will display some information.

First Run

The first time Config is run, there will be no settings stored, so default settings are shown. These settings are compatible with existing “Poor Man’s DATV” serialisers that use a chip to apply the FEC 1/2.

For PMDATV serialisers, select the com port number for the FT245 USB chip from CONTROL Com Port and leave the DATA Com Port as NONE.

Communications

When the FT2232H USB module on the serialiser has been configured, it appears as two COM ports. The system will have assigned numbers to these and these numbers will stay the same whichever USB port is used on the PC.

To find which numbers have been assigned:

- Plug the serialiser into a USB port

- Start Windows Control Panel – accessible from the Start button, bottom left of the screen

- Select SYSTEM

- Select HARDWARE

- Select DEVICE MANAGER

- Click on the plus sign next to PORTS

There should be two ports described as “USB Serial Port”. Make a note of them and close Control Panel and all its other windows.

If you are not sure which they are, unplug the serialiser from the USB port and they should disappear from the list.

- Click on the DATA COM Port box and select the number of the first port just noted.

- Click on the CONTROL Com Port box and select the number of the second port.

MPEG Input

Capture Device

Config calculates the bit rate which has to be set in the recording program. It is very important that the recording bit rate is set correctly or the system may not work properly. This bit rate varies with symbol rate and FEC. The HVR range of Hauppage captures cards, which are still being evaluated, need a slightly different calculation.

- Select the type of capture device in use: PVR or HVR

Input Method

Other ways of reading from the capture card are under development. For the moment leave this as Disk.

- Select Disk as the Input Method

Transport Stream

The transport stream is the name given to the data that is sent to the modulator. A symbol is 2 bits and the symbol rate is the number of symbols (in thousands) which are sent to the modulator every second.

Symbol Rate

- Select the required symbol rate from the list. Note that the Video bit rate field changes.

FEC

The Forward Error Correction, also known as Viterbi, adds extra bits to the transport stream to enable errors to be corrected at the receiver.

The higher the value of the fraction, the less error correction is added, allowing more video and audio data to be transmitted at any given symbol rate.

FEC 1/2 adds the most error correction.

- Select the required FEC rate from the list

Note that the Video bit rate field changes if the FEC changes.

FEC on PC / Serialiser

The FEC may be applied on the PC or on the serialiser. The advantage of applying the FEC on the serialiser is that it reduces the amount of data passing over the USB connection.

The saving reduces at the FEC fraction increases and there is not a lot of advantage selecting FEC on serialiser above 3/4.

At some symbol rates, the serialiser does have enough time to do the FEC and Config shows a warning message.

At some symbol rate and FEC combinations, the serialiser CPU is being over-clocked above its specification. Select FEC on PC if any problems are encountered.

- Select the required setting

TS Delay

There is a clock built into the transport stream (the PCR) and each frame of video contains the time at which it should be displayed, relative to this clock.

Frames naturally have to arrive at the receiver before their display time and the TS delay is the time at which the very first frame transmitted will arrive at the receiver before its display time.

In a 50Hz system, a frame is displayed every 40ms. If the data for every frame of data took exactly 40ms to transmit, then every frame would arrive at the receiver 200ms before its display time. The amount of data for each frame varies a great deal and although the output from the capture device is reasonably constant over long periods, it is not constant for short periods.

If the data for series of frames is taking longer than 40ms each to transmit, then they will arrive at the receiver closer to their display time. The TS Delay is a margin against frames arriving after their display time.

The TS Delay adds to the overall delay through the system. For ‘quiet’ talking- head shack shots, it may be possible to reduce it. For ‘busy’ shots, it may be necessary to increase it. There is scope for experimentation.

- Select the required TS Delay setting (0-500ms)

Buffer Delay

This sets the size of the USB output buffer on the PC.

The larger the value, the less chance of a transmission glitch if Windows gets busy. The smaller the value, the smaller the overall delay through the system.

- Select the required Buffer Delay setting (10-500ms)

Test Mode

- No Mod outputs suppressed carrier only at the nominal transmission frequency (NTF).

- LSB outputs a single carrier spaced symbol rate / 4 below the NTF.

- USB outputs a single carrier spaced symbol rate / 4 above the NTF.

- In Phase outputs two carriers spaced symbol rate / 2 above and below the NTF.

DigiLite Transmit must be running for test mode operation.

Channel Info

PIDs

The transport stream consists of a series of packets. Each packet has a packet id (PID).

Each component of a transport stream such as video, audio and program info is assigned a PID so that the receiver can extract just the parts it needs.

Generally these need not be changed from the defaults, but some receiving systems may require specific PIDs to be entered.

Some receivers will display a program even if the PIDs are changed after the program has been scanned into the receiver. Other receivers will not.

- Enter the required PID values (32-8190) without duplication

Channel Name

E.g. BBC1

The receiver may not register a change of channel name after the channel has been scanned.

Programme Name

E.g. Wimbledon Highlights

EPG Info

This appears when the Info or EPG buttons are pressed. E.g. Latest news from the courts.

Saving Settings

Click the SAVE button when it is red, to save the settings.

DigiLite Transmit will need to restart when most settings are changed and this will cause a glitch in transmission.

Windows Registry

For anyone interested search for DigiLite1

DigiLite Serialiser User Guide

The DigiLite Serialiser (see photo below) is the device that receives the transport stream data from a PC USB port and converts it into two bit streams (I and Q) for the modulator. Status indications and commands are transferred to / from the PC on a second channel. Do not insert the 28 pin dsPIC chip until the USB module has been configured.

Power Supply

Whilst the serialiser section of the card uses 3v taken from the USB 5v supply by the FT2232H sub-panel the modulator section requires 5v taken in turn from the 8v regulator that can be driven from 12v. Some sort of heatsink is advisable for these 78 series regulators.

LED Indications

Steady on / off at 1Hz Normal operation data is being received.

2 flashes every 2 seconds Waiting for data from the USB port.

3 flashes every 2 seconds An invalid symbol rate or FEC has been received. Operation continues at the previous settings.

6 flashes every 2 seconds Test mode active.

10 Pin Header

This is optional. It is intended to allow in-circuit programming of the dsPIC333 or the connection of an SD card reader which is planned for the future for generating a recorded signal where no pc is available.

Description of the circuit diagram.

The serial data that is generated by the DigiLite Transmit program is taken from the USB2 socket on your pc and is connected via the Mini-USB socket on the FT2232H sub-panel at the edge of the serialiser board.It is mounted on two twin 13 pin sockets (headers)CN2/ CN3. This allows replacing of the USB sub-panel in the event of a fault or an upgrade.

The software and drivers for the FT2232H can be downloaded from the manufacturers website. Run the install program from the pc with the USB lead connected. Do not plug the dsPIC333 in until this software is installed. The dsPIC333 (IC2) is in a 28 pin narrow DIL socket. This allows for programming any software updates. As a future option there is a header for in- circuit serial programming in the future with a SMD version of the PIC chip. If a card reader is used later most of the connections required also are available at this header (JP1).

The dsPIC333 is an interesting device. It is designed specifically for handling digital data streams at up to 40MIPS with lots of useful timing features.Refer to the manufacturers data sheet for more information.

The I and Q signals go to the 74AC574 latching flip-flops. The output of these eight latches are paralled to give four outputs ,I and Q and I* and Q* ensure accurate timing of I and Q phase components.Closely matched values of components here is important to ensure balance is maintained.

Then the signals pass to the Nyquist filters. A critical part of the modulator, the Nyquist filters, trim the skirts of the signal by filtering unwanted harmonics and reduce inter-symbol interference. Axial leaded inductors have been used here to ensure a high Q value, the smd versions tend to be lower Q, but for later versions G4EWJ is looking at a digital filter option which would require another chip adding to the board, a subpanel will be offerred if sucessful.

U3 and U4 are half dc rail regulators giving an accurate 1/2 voltage for the bias pots.This voltage is applied to the bottom end of the I and Q level pots giving the required (around 1.8v) dc offset for the inputs to modulator chip AD8346.

The modulator IC also requires a carrier of around -8dBm at the desired output frequency. This must be a good quality (low phase noise etc) signal. If you have less drive you may remove the attenuation at the input with resistors R27,R28,R38 currently set at about 12dB. The input can be capacitively coupled without the balun (with the other input AC grounded with 50R) but it is less efficient and can give poorer output waveforms.The -10dBm modulated output is AC coupled through C24 into a MMIC rf amplifier/buffer stage. Several further amplifying stages will be needed to get it to levels required for driving the PA stages, an inter-digital filter would also be an advantage. Where 50 ohm resistors are specified it is assumed that two 100 ohms will be used in parallel or even ‘piggy-backed’, this is easily achieved in smd.

What you will need

Hardware

A reasonably fast Windows XP, Vista or 7 computer with USB2 ports. A WINTV PVR PCI card with hardware MPEG2 encoder for your PC. (No longer available new so best purchased on Ebay or similar. Get the Hauppage disk when you buy one. Models PVR150,250 or 350 are fine. The PVR150 has phono sockets as well as S-Video inputs whereas the others only have the S-Video socket. The 350 will accept composite on the S-video socket)

A DigiLite Board

A FT2232H sub-panel to handle the USB2 from the PC. A Local Oscillator running at the required final frequency e.g. 1249Mhz. An Rf amplifier to raise the digital Rf output level.

Separate boards version complete system built by G0UHY

Software

- Drivers for the WINTV card. Drivers for the FT2232H module.

- The USB eeprom program for the FT2232H

- The PVR recording programme GBPVR X2. Freeware. (Ref 5)

- The PVR Config programme to set the parameters. Freeware. (Ref 5)

- Software for the Serialiser PIC chip

- DigiLite Serialiser Hex file.(Ref 3) (Or purchase a pre-programmed PIC chip from the BATC shop.) DigiLite Transmit.(Ref 3) DigiLite Config.(Ref 3)

Where to begin

It is worthwhile getting your PVR card and program running first. Once you are recording your video on your PC you are ready to get your DigiLite board built and running.There is a free download of Hauppage drivers at their website.(Ref 4) Once you have the WinTV card in and drivers running you can download and install the GB-PVR program which allows you to record the incoming video from the WinTV card composite or S-Video input socket.(Ref 5)

The NextPVR version can run with DigiLite but you will probably need the WinTV PVR program installed first, this is only available free using the disk that came with the WinTV card, so when buying second hand ensure that there is a disk with the card or you will have to buy a download version from Hauppage or use an earlier PVR.

The earlier GBPVR versions 1.3.11 and 1.4.7 work well.

Run the PVR Config program. Set the recording location to be either in the same folder as the DigiLite program or on whichever hard drive and folder you prefer. Full details will be given in the software download section.

GBPVR CONFIG:Follow the screen captures shown here to enter the required settings for the PVR program to use.

GBPVR Program

Click to start the PVR program and select: Live TV. If unable to select LiveTV or the viewing screen is just blank or red then your setup for the WINTV card is not correct yet. You should be able to watch the incoming video from your S-Video or composite feed. If you get a red screen go back to the PVR config and ensure that the program is using the correct video input.

GBPVR Main Menu

Go to the Recordings option. Choose Manual Recording from the sub-menu. If required change the start and stop times manually by highlighting the value and typing over it. Set it to start at (or even before) the current time. You should be able to record the video in an mpeg2 format.To monitor the recording go back to the main menu and select LiveTv and there will be an option to watch the recording as it happens. Do a brief recording then check it out with any mpeg playback program.It should have a .mpg tag not .ts Join the USB2.0 cable to the Serialiser board. If you havent yet installed the drivers for the USB FT2232H sub-panel do it now.(Remove the dsPIC333 chip first). Unplug the USB cable and re-insert the PIC chip. Reconect the USB cable and the LED on the serialiser panel should flash 2 flashes at a time. You now need to read out the file (while it is still recording) via the PC’s USB 2.0 port using the DigiLite Transmit program.

A full run-through of the software download and install will be in the next article complete with a full instructions on placing components on the smd board and getting digital ATV running without test gear.

Ref 1 www.m0dts.co.uk

Ref 2 jf.fourcadier.pagesperso-orange

Ref 3 www.g8ajn.tv

Ref 4 www.hauppauge.co.uk/site/support/support_support.html

Ref 5 download.cnet.com/GB-PVR/3000-12565_4-81654.html

Ref 6 www.ftdichip.com/Drivers/VCP.htm

If you find any of the above links broken please visit the DigiLite pages at www.g8ajn.tv

And Finally

If you really cannot wait to get building and can etch and drill your own boards there is a complete diy system build using separate serialiser and modulator boards by G4EWJ and G0UHY at my website(ref 3). There will not be any components available at this site. You will also need a good quality signal source (Low phase noise PLL Local oscillator) for the required 23cms output frequency. These are available from a number of sources, again details are on my website. It is intended that BATC Shop will hold pcbs and pre- programmed dsPIC333 serialiser chips and some harder to source components. Because of the low level Rf out from the modulator some amplification will be required and ideally some filtering too prior to your PA.

Due to the time involved in writing these articles and building the DigiLite boards I cannot respond to individual emails. Please ask any questions at the BATC Forum where one of the developers of the project will be happy to help you.

More details will accompany the constructional article.

The Digilite Project - Part 2

The hardware

The whole concept of this project was not just to keep the cost of getting started on DATV down but to make it as manageable as possible to home-construct. Assuming you have purchased a single board version of the DigiLite or have etched your own two board version, here is a suggested constructional approach.

Hardware Check list

- A reasonably fast Windows XP or 7 computer with USB2 ports.

- A WINTV PVR PCI card with hardware

- MPEG2 encoder for your PC. A DigiLite Board.

- A FT2232H sub-panel for the serialiser.

- A Local Oscillator running at the required final frequency e.g. 1249Mhz.

- A small tipped soldering iron

- Bench magnifier and lamp

There is sufficient output from the MMIC on the DigiLite board to feed to a satellite receiver which you can use for setting up the board.

The DigiLite software is the same for either the separate or single board versions. By starting with the serialiser section of the board you can get the USB panel installed and programmed and the dsPIC33F chip running with the once a second winking l.e.d confirming a data stream. Once that is OK you can concentrate on the more tightly packed modulator section.

Begin by soldering in all the smd integrated circuits. Of these the most tricky is the IC4 the modulator IC, AD8346. It is very narrow spacing between the legs, however with care and a magnifying lamp it is quite straightforward.

The DL board has been tinned ready for you to solder the chip, so with some very fine gauge solder place IC4 onto the board with the pin1 spot facing the preset pots and using a pointed tip soldering iron, solder pin 1 onto the board. Check the spacing on the other pins is OK and solder a pin on the other end of the IC to keep it in alignment.

Work your way round the IC soldering the single pins first, leaving those that are connected together on the board until last. If several pins get bridged by your soldering iron use solder-wick to soak up the excess solder and retry the soldering. If you are having a bridging problem allow the solder to cool down for a minute and then continue to remove the excess with Solder-wick. This will give time for the IC to cool down and avoid any risk of heat damage.

Do spend a little time checking with an ohm meter for any accidentally linked pins when the IC is in.

L5 is a low inductance coil and reduces the sidebands amplified by the MMIC. A small 0603 at 1uH it is necessary to decouple between it and R26/R41 with a capacitor of 1000pF or more.(1200pF is fine). R41 has been added across R26 to share the current drawn by the MMIC and avoid failure of this MMIC supply resistor.

The FT2232H USB sub-panel plugs into the two 26 pin header strips CN2 and CN3. Below this FT board, between the two headers, there are a few components and these should be fitted before the CN2/3 headers. The PIC chip IC2 has a 28 pin Narrow DIL socket, this may change in later panels to a solder-in smd and will be re-programmable via the 10 pin header JP1. This header can also be used to connect a SD card reader which will allow pre-recorded MPEG files to be replayed without the need for the usb/pc feed.

In earlier versions of the board the 5v USB DC line was used to generate the 3.3v line used by IC2. Later versions have their own 3v regulator to relieve the work load on the FT module.

Install the crystal,diodes,resistors (1% if possible) and capacitors. Fit up to C9 and R10. From here you can either set up the software for the serialiser and install GB-PVR, DigiLite Transmit etc. (ref 3) or move on and fit all the other components first.

The modulator section presents no other problems for construction, the oscillator input 1:1 balun, T1 is available from a couple of sources so the pads are intended to cope with either size. Being a 1:1balun, T1 can be fitted either way round as long as the wires connect the signal through, as you can see from the photograph the transformer has a location pin and in the prototype it was placed with that side facing the AD8346.

IC3 is a more standard pin spacing smd chip so is easier to work with. Fit all but the Nyquist filter coils, by fitting them last they can be kept low above the board avoiding components already fitted.

The Local Oscillator feeds in on JP2, the coaxial cable can be soldered directly onto the board if preferred. Keep unscreened wire to a minimum. You might need to alter the values of the 50R input attenuator R27,R28,R38 if your signal source is other than about +12dBm. If you can be sure you have about 6dBm to 10dBm local oscillator signal then the attenuator should be left out R28:o/c, R27:0R, R38:o/c Be warned : most problems with getting the modulator running properly has been due to too much local oscillator signal. If you suspect that this may a problem try doubling the amount of attenuation.

On our system we used a fixed frequency PLL sub-panel from Ultram Technologies (Ref 2). When ordering you will be asked to specify the output frequency you require. There is an article being prepared about a small add-on board to allow selection of 5 pre-set frequencies using this board.

The weak output from IC4 is lifted by MMIC MAR6 (U5) and buffered into the output socket. This 10 to 15dBm signal is too little to be of much use without further boosting. However it is fine to couple into the input of a satellite receiver, for example a Porty. A couple of amplifying stages will be needed to get to a similar level to that of a Comtech or other analogue transmitters/exciters.

You will be able to use your existing analogue PA and driver, but you will need to keep the drive levels down to stay in the linear portion of the PA. As the bandwidth of the digital signal is a quarter of that used by the analogue signal this will not be a problem, the digital signal will generally get into repeaters on much smaller power levels than analogue, indeed the lower the strength you can use to get a consistent signal in, the better the ˜quality" of signal you are likely to be sending.

Hauppage PVR CARD

WIN TV CARD. There are a number of different models that you can use, the DigiLite software is arranged around these boards, but they must be a PCI card with an MPEG2 encoder chip on it, not one where encoding is done in software. There are at least three versions of the cards, the common types are the 150, 250 and 350.

WinTV Model Numbers (printed on tuner can) 23xxx or 25xxx are PVR150. Model numbers 30xxx or 35xxx are PVR250. Model numbers 48xxx are PVR350. Model numbers 23xxx are PVR500(dual version).

Download the correct drivers for your version of the card from ref 1.

The Local Oscillator

The L.O. Board used originally has a MMIC on it to lift its output to the +12dB region at 1249Mhz. This was more than the modulator wanted and we found that removing or bypassing the MMIC gave a more suitable output level and avoided the need for an attenuator on the input to the modulator entirely.

A separate 8v regulator was fitted to the screened L.O. can to allow connection to the same 12v DC supply as the DigiLite board but avoiding the need for a heatsink on the regulator. However there is sufficient capability in hand for most oscillators in the on-board 8v regulator if you are prepared to bolt it to a heat sink. More details about adapting the Local Oscillator in the next article.

THE SOFTWARE

There is quite a lot of software to download and install but happily it is a ˜one-off" job only and once installed it is necessary to have just the PVR and DigiLite Transmit programs running to be sending digital pictures. I would recommend making a new folder on your PC into which you can download the various bits of software.

A check list

- DigiLite Config

- DigiLite Transmit

- DigiLite Serialiser Hex (not needed if Eeprom IC2 is already programmed.) FT2232H Drivers

- FT2232H Flash program.(Computer needs Microsoft .NET Framework 3.5 installed)

- GBPVR PVR program and Config

- DigiLite Serialiser

- A pdf of this section complete with screen shots is available at www.g8ajn.tv/dlsoftware3.html

The USB panel

FT223 2H

This is the device that connects to a high speed (480Mbps) USB 2.0 port and accepts the transport stream data from the PC. Doing the FEC on the serialiser reduces the data rate over the USB connection. The serialiser has a second communication channel which is used to receive control information from DigiLite Transmit to set the required symbol rate and FEC. The serialiser has been used successfully at symbol rates between 1250k and 6250k. Several symbol rates are pre-programmed into the system.

The FT2232H sub-panel requires drivers and a program to run with the DigiLite software. Get these from Ref5. (CDM20814.exe) On the FTDI webpage,scroll down the FTDI page, select the Windows row from the table

˜Currently Supported VCP Drivers:" at the bottom half of the page. Click on˜Available as setup executable''.

You might prefer to go to the DigiLite website (ref 3) where the links are all available together and will be kept up to date.

If during the install you are asked for a floppy drive disk just change the drive letter and point it to your downloaded file. Download and run the FTProgv2.2 which is used to flash the EEprom on the panel. (You will need to have .NET 3.5 on your pc to run it though, but it is a free download from Microsoft and you will be prompted to download it).

FT2232H USB Module Installation

The FT2232H USB module has two input/output ports, either of which can be configured to be one of several device types. The factory configuration is two uarts (serial ports). For DigiLite, the first port needs to be configured as a FIFO (first in first out byte memory). Screen shots of this procedure can be found on the DigiLite web site.Ref 7

Preparation

- Do not insert the dsPIC chip until the FT2232H module has been configured.

- Download and unzip the FT2232H VCP (not D2XX) drivers from here: http://www.ftdichip.com/Drivers/VCP htm

- Download and unzip the FT2232H Configuration program (FT_PROG) from here: http://www.ftdichip.com/Support/Utilities/FT_Prog_v2.4.zip

- With the FT2232H installed in a serialiser, connect it to a USB port on the PC.

- Give the location of the drivers if asked. You may need to do this several times until all the components of the FT2232H drivers have been installed.

Editing the Configuration

- With the FT2232H connected, run FT_PROG.

- FT_PROG needs Microsoft .Net Framework 3.5. You may be prompted to allow this to be installed if it is not already on your PC. It may be several 10s of MB.

- Make sure that the EEPROM tab at the top of the window is selected.

- Click DEVICES and then SCAN AND PARSE. The FT2232H should be detected. If there are other USB devices from the same manufacturer connected, click on the DEVICE line for each device in the left hand box until the FT2232H is found.

- In the left hand box, click USB Config Descriptor. In the right hand box, set Max Bus Power to 250mA.

- In the left hand box, click USB String Descriptors. In the right hand box, tick Serial Number Enabled. In the right hand box, untick Auto Generate Serial No. In the right hand box, set Serial Number to DATV.

- In the left hand box, click on the + sign next to Hardware Specific.

- In the left hand box, click on the + sign next to Port A.

- In the left hand box, click on Hardware on the next line down. In the right hand box, select 245 FIFO.

- In the left hand box, click on Driver on the next line down. In the right hand box, click on Virtual Com Port (if not already selected).

- In the left hand box, click on the + sign next to Port B.

- In the left hand box, click on Hardware on the next line down. In the right hand box, select RS232 UART (if not already selected).

- In the left hand box, click on Driver. In the right hand box, click on Virtual Com Port (if not already set to this).

Programming the Configuration

- Near the top of the Window, click DEVICES and then click PROGRAM. A new window appears. If more than one device is shown, make sure that only the FT2232H device is ticked. Look at the previous (main) window for the device number.

- Click PROGRAM It should only take a few seconds and then Finished Programming should appear in the bottom left of this window.

- Close the programming window, close FT_PROG, disconnect the FT2232H and reconnect.

- Go back up to Editing the Configuration and check that Port A Hardware is set to 245 FIFO.

- Close FT_PROG.

Finding which COM ports have been assigned

Look in Windows Control Panel / System / Hardware / Device Manager / Ports. They should appear as USB Serial Port.

If you are not sure which are the FT2232H ports, unplug the FT2232H and reconnect to see which ports disappear and reappear.

After configuration, these port numbers will remain the same whichever USB port the FT2232H is connected to.

In DigiLite Config, enter the lower port number as the DATA port and the higher as the CONTROL port.

The Serialiser

Once the USB panel has been programmed, IC2, the dsPIC33F device, can be programmed. If you have had it programmed for you then you can insert the device in its socket and proceed to the next step. If not already done, then download DigiLite Serialiser Hexfile and program IC2 with a suitable PIC chip burner board. Details of programming the PIC ˜in circuit" will be given in later articles When completed insert the chip into its socket and continue.

If you have not yet downloaded DigiLite Config and DigiLite Transmit from Ref3. get them now. Run the DL Config program. DigiLite Config is the program that you use to set the symbol rate and FEC and also the channel name and program details. Settings are stored in the Windows registry, which DigiLite Transmit monitors continually to look for any changes in transmission parameters. You should see a screen window with a number of different options. If you are not sure which settings to use, go for these:

Symbol Rate 4000, FEC ½ , FEC on serialiser, Test Mode :OFF, Capture device: PVR, Input Method : Disk,

The Video Bit Rate setting will alter itself with the different settings like Symbol Rate and FEC, 2920 is a typical value but whatever the value make a note of it as you will need to enter this value into the PVR configure program later on.

The COM PORTS will be those set by Windows and you can see them in your Windows Control Panel/ System / Hardware / Device Manager. Look for the Ports (COM & LPT1) heading, click the + to open the folder. Plug the USB2 cable into the FT2232H USB sub-panel and look to see which port numbers appear in this folder. Make a note of the two numbers then go to DigiLite Config and enter the numbers in the boxes in the left-hand corner of the window, lowest number at the top (Data COM Port) and the higher number at the bottom (CONTROL COM Port).

The other boxes like PID and Channel info are optional and you can enter your call-sign here if you wish. Of course you can always come back and change settings, even while Transmit is running. Details of the Test functions will be discussed later on.

PERSONAL VIDEO RECORDER

WIN TV PVR

Not all versions of the WinTV PVR work satisfactorily with DigiLite Transmit, but try a download of the WINTV6 (the current version) PVR (not just the drivers. The drivers are available free but unless you have a valid Hauppage CD in the drive you will have to pay to download the WinTV PVR).

- If you have any GB-PVR files in your PC click the un-install GB-PVR option in Windows/ Control Panel/Add or Remove Programs.

- Install the WinTV using the setup.exe file. With the WINTV program running Select the MENU button then Suite Manager.

- Select Scan tab: set Scan UK : Cable: PAL_BGHIDK

- Select Sources tab : Set

- Input Sources : Composite Source

- Video Format: Select PAL_BGHIDK

- In Channel box enter a name e.g. Aux Video In

- Select the MOVIES/MPEG tabs and set the location you want the temporary recordings to be placed in. e.g C:/ Temp

- Set Quality to MPEG2 2.0Mb/Sec

- Click the Red record button.

A small window should drop down showing the recording file name and timing. You should be able to see your video input in the WinTV window. You can now run DigiLite Transmit. If you have any problem with WinTV PVR you can uninstall it and try GB_ PVR instead. If, after closing the WinTV window you are unable to restart it, use control+alt+delete and click the Processes tab and highlight WinTV.exe and click the End Process button.

GB_PVR

GBPVR is a free PVR (personal video recorder) program. The GBPVR X2 software works well with the DigiLite software. Versions 1.3.11 & 1.4.7 have been used successfully. Later versions like NextPVR seem only to work with later number WINTV boards. GBPVR requires a certain standard of video graphics card to run, even if you do not actually want to watch the video on that PC. Older graphics cards may have problems.

On the GBPVR download site, click the smaller green button marked 'DOWNLOAD 15.22MB'

GBPVR CONFIG

Follow the settings here for the GBPVR program to use. After finishing the Config setup then you can run the GBPVR program.

1. Start GBPVR Config

2. Click Capture Sources

3. Click Add

4. Make up a Source Name

5. Select Recording Source = Analog Recording Plugin

6. Select EPG Source = None

7. Select Channel Changer = No Channel Changer Required

8. Click Settings next to Recording Source

9. Under Capture Devices, tick Only show devices detected in this machine The PVR250 / 350 may show extra cards. Select the one you have.

10. Select Country

11. Select Board Number = Capture Device #1

12. Select Source - normally Composite, External Tuner for phono input

13. Select Quality Profile Settings = Medium Quality Set Medium Quality in GBPVR when making a recording later.

14. Click Edit

15. Select Video Resolution = NTSC 720x480 / PAL 720x576

16. Tick Constant

17. Set Bit Rate as given by DigiLite Config

18. Select Audio Bit Rate = 192

19. Select Audio Sample Rate = 48kHz

20. Click OK on all the GBPVR Config windows to exit from GBPVR Config

21. Start GBPVR Config again

22. Click Capture Sources

23. Click on the capture source you entered above and click Edit

24. Click Add

25. Make up a Channel Name

26. Set Channel Number = 1

27. Click OK

28. Click OK to close the Edit Recording Source window

29. Click Directories

30. The Recordings Directory can be left at the default, but if you have a second physical hard drive, it is beneficial to record to this. In this case, browse to the folder you would like to record to. GBPVR will add the folder ˜Manual Recordings" to the folder you specify and record to there.

31. Click OK to exit from GBPVR Config

GBPVR Program

Click to start the PVR program and select: Live TV. If unable to select LiveTV or the viewing screen is just blank or red then your setup for the WINTV card is not correct yet. You should be able to watch the incoming video from your S-Video or composite feed. If you get a red screen go back to the PVR Config and ensure that the program is using the correct video input.

You will need to ensure that you copy the four digit number shown in DigiLite Config Video Bit Rate box window and enter it into PVR Config Edit Capture Setting / Bit Rate .

Go to the Recordings option. Choose Manual Recording from the sub-menu. If required, change the start and stop times manually by highlighting the value and typing over it. Set it to start at (or even before) the current time. The GBPVR record start time will default to the next 10 minute boundary. You should be now be able to record the video in an mpeg2 format. The GBPVR icon goes green when recording.

To monitor the recording go back to the main menu and select LiveTv and there will be an option to monitor the recording. You can minimise this window if preferred.

To stop or modify a recording, click on Pending. Never use the ˜Stop / Restart Recording Service" items on the GBPVR menu.

DigiLite Transmit

DigiLite Transmit is the program that reads the recorded data from hard disk immediately it has been written. The data is in Program Stream format, which is very similar to the format used on DVDs. The video and audio are extracted and converted into DVB-S transport stream format, which is the format used by European broadcasters to deliver standard definition programs via satellite. This means that a cheap FTA (free to air) satellite box may be used to receive the transmission. Other data is placed in the transport stream such as date and time, channel name, program name and Electronic Program Guide (EPG) info. The transport stream data is sent to the serialiser via a USB port by DigiLite Transmit.

We now need to read out the file (while it is still recording) via the PC's usb2 port using the DigiLite Transmit program. Ensure that the settings on the DigiLite CONFIG window are as described. (the usb port numbers will vary. With the serialiser plugged in, find yours in Windows/control Panel/Hardware/ Device Manager/System. Look under Ports). Close the Config window and click the DigiLite Transmit icon.

A DOS style window should appear and the program should have found the recording location and start to read it out. If you select other symbol rates and FECs, this value will change. Don't forget to clear out (i.e. delete) the old recording files in the folder where you temporarily store them now and then. You can do this from within GB-PVR or by Windows Explorer. After a lot of recordings and deletions a de-fragment of the hard drive might be wise.

So hopefully we now have a recording under way using the PVR and clicking on DL Transmit program with the USB cable connected the Led on the serialiser should change from a double flash sequence to a once a second flash. This tell us that all is well as far as the serialiser software is concerned and we can then move to the modulator and Local Oscillator setup.

Some initial DC voltage settings

Ensure the regulators are working properly. With a dc supply of 12v the DigiLite board should draw about 150mA. The local oscillator described here draws 60mA. Sliders of I & Q Bias presets R29/R30 should be set to mid- way initially.(2.1v on sliders) Set I & Q Level presets R16/R23 to mid-way. ( 4v on sliders) Check IC4 pin 11 (output) for between 3.5 and 4v. Check for approx. 4v on output leg of MMIC.

If you have a different local oscillator and are not sure of its output level, Norman G3UXR has measured the output voltage generated using the simple power meter described in CQ-TV 187 page 43. With the MMIC not in circuit, the output voltage of the meter is about 0.025v . (Supply 8 volt . Load 50 ohm within power head). This is what you should be aiming for if you have a different local oscillator. The phase noise figure is critical on the local oscillator so "any old signal" will not do. Phase noise of the Ultram board is -96dBc at 10kHz offset.

Fully screen the vco/local oscillator board. It can radiate quite a strong signal that could get indirectly into the modulator. Connect the Local Oscillator to JP2 by a short coax cable. Connect the output connector or cable to the capacitor C31-which if preferred can be a wire-ended capacitor rather than smd (between 12pf and 25pF) to a SMA socket or similar. If you are fitting a smd directly to the edge of the board it is advisable to solder the top and bottom earth planes to the body of the socket.

If you have a Spectrum Analyser you can use the test options in DL Config to switch on/off the upper or lower sidebands, modulated output or 'in phase'. Options are selected by clicking on the SAVE button. Set to OFF to resume normal use.

Below are three photos supplied by Rob M0DTS, left to right: Lower Sideband Only; Output after tweaking; Upper Sideband Only.

If you don't have a Spectrum Analyser you can use the on-screen signal meter of your satellite receiver to get very close to an ideal setup. Connect your receiver using a small 5cm aerial wire rather than a direct connection as there is a risk of damage from ac leakage.

The picture to the right is of the Comag Porty/SL55 receiver where the strength and quality levels are shown. This was set up directly from build without a Spectrum Analyser using only this on- screen info screen. Before trying to tune in to the DigiLite signal ensure that the PVR is recording ok and that the DigiLite Transmit is finding the file to read out ok and that the LED on the board is winking once per second.

Initially you should be looking for a signal strength of at at least 60%.When you begin to set up your DigiLite you should set all the preset pots to mid- way. In some cases this will give you a usable digital signal, but assuming not, try turning the I Level (R23) a few degrees clockwise keeping an eye on the signal meter. You are looking for a quality reading to appear. Move to Q Level pot (R16) and turn that a few degrees clockwise. Continue to nudge the pots round until a signal appears. When it does you may try the other two pots the I and Q bias pots to give the highest quality reading.

If after all this you still get no correct digital output you need to ensure that the Local Oscillator level is not too high or too low. Without test gear I would suggest setting pots back to mid-way and try bypassing the input attenuator if you are using one.

Maybe you could try various low value resistors across the input socket JP2 starting with 56 ohms and dropping to 10 ohms to see if too much signal is the problem. A series trimmer capacitor could be tried having a value of 2-20pF or similar.

Clearly there are many possible constructional errors that might be stopping it running correctly, make sure that smd components are ˜square" onto their solder pads, ICs are correctly placed and do an ohms check between the pins of IC4 ensuring that only the desired .

Satellite Receiver

Some satellite receivers will only lock in the channel you are using once they receive a valid digital signal.

1. On the Porty (and probably most other satellite boxes too) use the MENU to get to the INSTALLATION MENU enter 0000 for the password and select ANTENNA SETTING option.

2. Select an unwanted satellite TRANSPONDER highlight it and click the right arrow on the remote control. Scroll up the right hand window through the list of settings until you get to NewTP. Select that by pressing the OK button.

3. A sub-window will appear and there you can enter the settings for your DigiLite signal. Because of the I.F. used by a LNB when receiving via a dish, you need to add 10,000 to your required frequency. For example, if your DigiLite Local Oscillator is running on 1249Mhz you would enter 11249 for the FREQUENCY. Move down to the SYMBOL RATE and enter the 4000 (for 4Ms/s) or whatever you have set in the CONFIG programs.

4. For the FEC settings I advise selecting AUTO but you can set a specific error correction rate if preferred or if AUTO is not an option on your receiver.

5. The Polarity is not relevant as we are not using a LNB.Click OK to close the window.

6. In the left hand window move down to highlight the LNB FREQUENCY. Use the right arrow to get to the right- hand window and scroll up or down to find User Define.Click OK and set it to 10000. Click OK when prompted to store the changes.

7. Other settings are not relevant so scroll down to Start Search , use the right arrow to select Transponder and click OK.

8. Whatever your receiver the same basic settings will apply, place a 1 in front of the required frequency and set the Data Rate and FEC, and a LNB offset of 10000.

Once all these settings are made and assuming you have added whatever amplification you require to get sufficent drive for your PA it is really simple to get running.

To get on-air

Start your PVR program either WinTV or GBPVR (your can record four hours comfortably on a hard drive so you can leave it running even if you are not actually on-air all that time, you can just delete the file when you have finished). Set the PVR program to record. Run the DLTransmit program. (minimise the windows once running to clear your screen area)

Marvel at the noise-free transmitted pictures. Thats it!

Check the BATC Forum for other suggestions and specific help.

The concluding section will describe setting up the output, a small add-on PIC board designed by G8BYI that allows the Ultram Technologies Local Oscillator to be switched to one of five preset frequencies and we will be discussing possible future upgrades and developments.

Parts List

Due to ever-changing availability of parts and their part numbers frequently changing I have decided to keep an electronic version on-line to allow regular updates to be incorporated. Please download a pdf from the DigiLite website.

Check for availablity of major items at the BATC Shop first.

- Ref 1: www.hauppauge.co.uk/site/support/support_support.html

- Ref 2: Ultram Technologies (Ebay : search for Phase- Locked Oscillators)

- Ref 3: www.g8ajn.tv

- Ref 4: download.cnet.com/GB- PVR/3000-12565_4-81654.html

- Ref 5: www.ftdichip.com/Drivers/VCP. htm

- Ref 6: www.ftdichip.com/Support/ Utilities.htm

- Ref 7: www.g8ajn.tv/dlsoftware3.html

The Digilite Project - Part 3

Additions to the Parts List

There are several devices that are not part of the original parts list as they do not appear on the circuit diagram but which are needed to get the system running...

The USB interface sub-panel FT2232H that plugs into the board via the two dual 13 pin headers CN2 and CN3.This device has to be programmed. It is now available preprogrammed from the batc shop ready to plug in and use. Farnell part No:169-7465

The local oscillator giving an output of up to 10dBm at the required modulator output frequency.

The PIC 16F628A IC programmed for use in the G8BYI add-on preset tuning panel.

The above items are available from the batc shop.

The WinTv PVR150,250 PCI capture card. (Second-hand. No longer manufactured). The external PVR2 version will work but getting it installed can be very fussy.

Constructional notes

Version 5.6 pcb only:

- Scrape away the green protective coating for mounting the MMIC U5 depending on the shape of the device you are using, there are several alternative smd devices available.

- A 100pF capacitor can be used to bypass the stage if you wish to amplify the Rf in a separate unit.

- Do not mount the crystal too low to the board, it could short out the capacitors, it might be better to leave a few millimetres gap and if using a full height crystal use glue gun adhesive or similar to support it vertically. Spacing has been increased from version 5.7

- Ensure the modification around R20 has been done (corrected from v 5.7).

- Ensure that C20 is grounded at the lower end (corrected from v 5.7).

- Add a 0.3μF (radial or axial) on the 12v DC input pin to ground (SMD added from v5.7).

Full details are on the batc forum or on the DigiLite website.

All versions

The 8v regulator can be used to run the local oscillator board if necessary, but it would be better to use a separate regulator. It is however well within the capabilities of the 8V regulator to run the entire sysytem (About 150mA) you will have to mount it on a heat sink or on to the metal of the box you are fitting it into as it also supplies input to the 5v and 3.3v regulators to allow up to 16v dc input.

Early circuit diagrams show the earth return resistors on the bias pots R31, R35 as 100 ohms, they have been changed to 1k resistors to improve the range of the bias pots.

If you do not wish to use the smd tantalum electrolytics, regular radial capacitors will work ok, just bend the ends of the legs into an 'L' shape to fit the solder pads. Support with glue gun adhesive etc.

All through-holes 'vias' are solder plated so soldering those components on the bottom side of the board is sufficient for a good connection without needing to solder the top connection.

JP1 is an optional header to allow for future options including SD card reader and In-circuit programming of the PIC chip. No need to fit it at this time.

The smaller headers (2 way and 3 way ) can be cut from a 10 way type.

The half-rail regulators U3/U4 have legs that are quite close together so care should be taken not to s/c the tracks when fitting them. Spacing widened on later version boards.

The input balun can be fitted either way round as it is a 1:1 ratio.

Photographs of Spectrum Analyser displays of DigiLite outputs supplied by Rob M0DTS.

Getting the level of the local oscillator right is very important. Too much and it will break through the top of the output waveform and the decoder will not accept the signal. When you first switch on your completed board you may get a mess of carriers and unwanted signals as seen in the photo but careful balancing of the Upper and the Lower Sidebands to get them equal (you can switch them off/on with the DigiLite Transmit programme if it helps) using the four presets as described before you should end up with a digital signal that will give good results on commercial receivers at 4Ms/s.

Get the 'shoulders' balanced and then check the signal out on your satellite receiver. You probably will end up tweaking the pots to get a high quality reading on the OSG anyway, so with patience you can manage a good quality signal without a spectrum analyser.

Initial check list

Start WinTV7 or GB-PVR, set it to record. Open Windows Explorer and look on the main C: drive under Temp folder. Look for recordings by the WinTv or GB-PVR programmes. Check out previous attempts to record by double-clicking the file and see that they replay as mpeg files ok.

Run the DigiLite Config programme. Ensure that the COM port numbers are the same as those on the Control Panel/Devices list. Close the programme. Click the DigiLite Transmit programme. Ensure that the Transmit is running correctly and that there is a line of changing data on the 'Command Prompt' screen as the stream is sent to the serialiser.

The LED on the serialiser should be winking in an equal on-off every second. Connect the output of the DigiLite into the aerial connector of your satellite box (watch out for the dc on the cable!)Loose coupling should be fine.

Ensure that the signal strength on the info screen is at least 60%. Adjust the four presets as previously described, very small, slow movements watch the info screen on your satellite receiver / tv there should eventually be a flash of picture or better still a quality reading as well.

Who needs a Spectrum Analyser anyway?

I have been involved in getting a couple of boards running locally for guys without Spectrum Analysers . In all cases when the dc levels appear to be correct and wiring/soldering errors have been eliminated, the fault is TOO MUCH LOCAL OSCILLATOR signal, sometimes induced into the board from the poorly screened local oscillator can and cable. Keep it short, keep it grounded and seal the screening can on the oscillator as if it was gas rather than signal that was trying to escape!

If you are not using the Ultram VCO board make sure that the phase noise figure is good enough for digital modulation. If you are using the Ultram, take the local oscillator output from the input to the MMIC on the VCO board. If preferred you can remove the MMIC entirely.

There is sufficient signal from the VCO chip to operate the modulator chip via the balun but may need the three attenuator resistors on the input of DigiLite board removed and R27 (82ohm) replaced with a 0 ohm resistor to couple the local oscillator signal to the balun.

Hook the output of the DigiLite board to the aerial socket of the satellite receiver (watch the dc line to the lnb!) and aim to get at least 60% signal level. If you wish you might try in-line attenuators on the local oscillator feed. Don't use home made attenuator boards for the reasons given above. Here is my preferred method of initial setup:

Set all four pots to mid-way.

Gently and slowly edge one of the 'level' pots watching the satellite box info display. It takes a moment or two for the quality reading to kick in.Once it has, move to the other pot and aim to raise the level of the quality reading until the level drops back down again.

If no Quality reading leave the 'level' pots at centre travel and adjust the two bias pots av small nudge clockwise and repeat the settings described above of the level pots. The dc readings on the level pots are also affected by the dc coming out of the 74AC574 IC1. Check the 3v line is within tolerance. Check voltages on the output pins of IC1. Always read IC voltages on the IC pins not on nearby components.

The small amount of bandwidth used by the digital signal means that by dropping to just 2Ms/s it is possible to squeeze a colour tv signal into the 70cm band. It requires a slightly different version of the modulator chip and changes to the filter coils otherwise it is the same circuit and board. Here is more information from Malcolm who has successfully built one.

Running DigiLite on 70cm

by Malcolm G0UHY

I have managed to construct a version of the DigiLite for use on the 70cm band. I'm using the same serialiser and modulator circuit. Although some people have managed to get the modulator to work on 70cm using the AD8346 chip, it is not really intended to run at that frequency. I have therefore replaced the AD8346 with an AD8345 which is identical physically but is intended to run at lower frequencies.

The Nyquist filter also needs to be modified to allow the transmitter to operate at 2Ms/s and keep the required bandwidth down. Change the Nyquist filter values to 1.2nF/33uH/3.9nF/27uH/1.2nF

The VCO used in this design is a synthesiser kit sold by SDR kits. The good thing about this is it is easily tuned over the 70cm band and comes with an LCD display. Memories and separate VFOs are also provided making operation and frequency changing simple.

The O/P from the DigiLite is quite low and I'm using a separate 'brick' PA which gives about 60W out. The unit is still small, even with a suitable heatsink, making it ideal for portable use with a laptop. On the receive side I'm using a converted commercial up-converter available from e Bay (details on Rob, M0DTS's site ) and a standard digital satellite receiver.

Here is further information on using DigiLite on 70cms from G8BYI:

To set up PVR for 2MS/s, go into GBPVR's Config utility and edit the settings for Custom1 Quality.

Video Resolution PAL 352/576 : Bit Rate 1500 Constant : Audio Bit Rate 192 : Audio Sample Rate 48kHz Save and exit.

1500 is actually too fast for 2MS/s, but GBPVR won't allow a lower setting. To get around this, you need to find GBPVRs install directory and edit DIRECT.INI

Look for the section [SETUP-Custom1 Quality]. Change the Bit Rate to 1350. Save and exit.

Having done this, if you try to edit the Custom1 Quality settings with GBPVR, Config will crash. A full- function tuning board with LCD will be described in a future edition of CQTV If you want to use the DigiLite as a mobile unit you will need a laptop pc and an external WinTV PVR2 capture unit.

The BATC Shop now stocks the 437MHz Ultram board.

Digilite: the future

Brian G4EWJ is looking into improving (narrowing) the transmitted signal bandwidth by improved digital filtering. This might be achieved with a small add-on board.

Using the transport stream directly from the Win TV card it might be possible to avoid the need to use a hard drive. As future improvements come along, In-Circuit Programming of the PIC chip IC2 will mean that a smaller smd version can be used and no socket will be required.

The local oscillator and controller could be mounted on the same board. A fully tunable VCO controller with LCD display by Richard G8BYI and will appear as a separate CQ-TV article shortly.

This is an evolving system but has the benefit of being very manageable for the home constructor and with the help available on the BATC Forum DigiLite pages there is no excuse for anyone not tackling and discovering digital ATV.

Thanks to the BATC shop all the difficult to source parts are now easily available and the cost is a fraction of that of commercial encoding systems.

Soldering in the tricky IC3 modulator chip may put some people off and it is envisaged that some pcbs with the chips already fitted could be made available if there is enough demand.

The Project is a real team effort and there are a number of very generous people who have donated their time, hardware and software designs to enable me to assemble all this information for your benefit. Thanks in particular to Brian G4EWJ, Rob M0DTS, Malcolm G0UHY and Richard G8BYI but also to many others who have passed on their suggestions and improvements to enable the Project to get to this stage.

I repeat that I have only assembled the information others have provided and squeezed it into one printed circuit board. I take no credit for anything else herein. Please respect the individual rights of the software providers when you download it and please do not alter it and publish it elsewhere without the agreement of the authors. Having said that we encourage you to move the project on. If you have some bright ideas on how it can be improved let us all know via the batc forum. Do tell us how you get on with your digital ATV build.

Of course if you have any problems building your DigiLite the guys will all be there to help you sort it out. On behalf of all the DigiLite Project Team, we hope you enjoy experimenting with Digital ATV.

Dave Kenward G8AJN

Simple tuning add-on

by Richard G8BYI

Here is a very useful add-on for the Utram Tech local oscillator used with the DigiLite board. The original oscillator is a single frequency device, but by replacing the on-board 8pin PIC with this simple unit you can select one of five preset channels using a single press button switch. The on-board regulator allows it to run from 8 to18 volts dc.

Adapting the ULTRAM local oscillator

The Local Oscillator used in our version uses a low cost commercially made board by Ultram Technologies which uses a digitally controlled oscillator/ pll IC ADF4360 to generate the required output frequency. The parameters for the oscillator are applied at switch-on by the 8pin PIC chip12F629.

In order to keep the costs to a minimum the Ultram Tech. board comes preset to a single frequency chosen by the purchaser. It is not fitted in any casing and has no output connector fitted.

Richard G8BYI has designed an add-on board which replaces the 8-pin PIC chip with a larger device PIC16F628 mounted on a small SMD single-sided add-on board . The benefit of using this is to get 5 preset frequencies which can be stepped through with a press-button. By using LEDs as indicators and a single press-button switch the cost is minimal.

The five common frequencies are 1244,1248,1249,1262,1280 built into the software but they can be replaced by re-programming if other frequencies are required. If you get a local oscillator board and wish to use the 5 channel add-on you will need to remove the 8 pin PIC chip and connect the 3 wires from the add-on board connector JP1 to the pins as shown.

- pin 1 to oscillator board ground.

- pin 2 to osc board pin 7 (Data)

- pin 3 to osc board pin 3 (LE)

- pin 4 +5v connection. Not needed.

- pin 5 to osc board pin 6 (Clock)

The connector can omitted and the boards can be wired direct if preferred.

Remove the PIC chip and connect the three wires from the new PIC board to pads 3,6,7.The DC HT (Max 9 volt) connects to the tab at top right of the picture. For the DigiLite board the extra gain of the MMIC is not required so the output should be taken after the coupling capacitor on the input to the MMIC. The full output might be useful for other projects. It would be best to run the three wires in via feedthough capacitors, but keep the wires short as possible, I have used ribbon cable about 3 inches long without problems, so its up to you.

Thanks to Richard G8BYI for permission to use his circuit and software.

Download the latest version of the software at http://www.g8ajn.tv/dlother3.html

The preset channels can be changed in software to suit other countries. An alternative selection has now been programmed by Richard to suit the USA channels. There is no need to use the extra gain from the MMIC as you will then need to attenuate it back down again at the input to the DigiLite board. Take your output connection from the input side of the MMIC (see photo ) and remove any attenuation on the input to the DigiLite board. The MMIC can be removed if preferred. I would leave it in as it can be used to provide a useful 23cms signal source for other projects.If you need to increase the attenuation on the DigiLite board input, try R27=56 and R28 and R38=270 (about 20dB) modifying the Ultram VCO board

Help! My DigiLite does not work!

The best approach to fault-finding is to check the separate areas of the DigiLite and follow the signal path in each area.

THE DATA : Is the WinTv recording onto your hard drive ok? Find the file you have recorded and click on it to run it as a mpeg2 video file. It should run on your pc with your installed viewer program eg Windows Media Player.

THE USB INTERFACE : Is the LED on the DigiLite(DL) winking once a second? If not, investigate the USB com port on your Windows/ Control Panel/Hardware Devices to ensure that the USB is being recognised by the PC.Check your settings on the DL Config program and ensure the DL Transmit program is finding the mpeg file on your drive.

THE BOARD: Assuming all the above check out ok and the led is good, you may have a problem with your construction. There are lots of quite close connections on the DL board so a good magnifying bench lamp is essential. Check across the board for poorly soldered components. SMD components can be 'askew' and that will allow short circuits to nearby parts. Wrong values are another possibility.

VOLTAGES: The board draws about 140mA at 12v in. Check the 3v,5v and 8v lines are ok. The pots R29/R30 (I & Q Bias) should have about 2.1v on their sliders, R16/R23 (I & Q Level) should have 4v on sliders. The modulator chip IC4 should have 3.5 to 4 v on its out pin 11.The output leg of the MMIC should have about 4v on it. Using a 'scope to see the waveforms from the serialiser into the modulator section is difficult as the data appears 'jumbled &distorted' but it should be very similar on the I and Q lines.

One of the most common causes of no digital output is the level of the local oscillator in on JP2 being too high . If you are using the Ultram board take the drive from before the MMIC and remove the DL input attenuator resistors R28 and R38 and fitting a link, 0R smd, as R27. This should get you a local oscillator input of the correct level for the mod chip.

I have been involved in getting a couple of boards running locally for guys without Spectrum Analysers . In all cases when the dc levels appear to be correct and wiring/soldering errors have been eliminated, the fault is TOO MUCH LOCAL OSCILLATOR signal, sometimes induced into the board from the poorly screened local oscillator can and cable. Keep it short, keep it grounded and seal the screening can on the oscillator as if it was gas rather than rf signal that was trying to escape!

If you are not using the Ultram VCO board make sure that the phase noise figure is good enough for digital modulation. If you are using the Ultram, take the local oscillator output from the input to the MMIC on the VCO board.

There is sufficient signal from the VCO chip to operate the modulator chip via the balun but may need the three attenuator resistors on the input of DigiLite board removed and R27 (82ohm) replaced with a 0 ohm resistor to couple the local oscillator signal to the balun.

Hook the output of the DigiLite board to the aerial socket of the satellite receiver (watch the dc line to the lnb!)directly or lose coupled twisted wires and aim to get at least 60% signal level. Signals bouncing around a room will even cancel out and cause great difficulties in setting up .

If you wish you might try in-line attenuators on the local oscillator feed. Don't use unscreened home made attenuator boards for the reasons given above. Here is my preferred method of initial setup: Set all four pots to mid-way. Gently and slowly edge one of the 'level' pots watching the satellite box info display. It takes a moment or two for the quality reading to kick in.Once it has, move to the other pot and aim to raise the level of the quality reading until the level drops back down again. If no Quality reading leave the 'level' pots at centre travel and adjust the two bias pots a small nudge clockwise and repeat the settings described above of the level pots. The dc readings on the level pots are also affected by the dc coming out of the 74AC574 IC1. Check the 3v line is within tolerance. Check voltages on the output pins of IC1. Always read IC voltages on the IC pins not on nearby components. Patience gets results. Visit the batc forum and we will talk you to success!

Good luck,

Dave G8AJN

A Card Reader for the DigiLite board

From information supplied by G4EWJ with photos by G4KLB, article compiled by Dave Kenward, G8AJN

The DigiLite has proved to be a very successful project with several hundred boards sold across the World. Apart from being reasonably inexpensive it actually allows for home construction of a digital ATV encoder.

For some time Brian G4EWJ who wrote the original software has been working on an add-on to allow the use of a memory card to store the transport stream file which will allow for the playback of previously recorded material. This can be a carousel of files on the card or just a single file.

The advantage of this is that a computer is not required in order to retransmit a recorded file. You will still require a PC on which to make the original recording, but if going portable or needing a test signal it could be very useful.

In order to allow for the extra software the dsPIC33 chip (IC2) will need to be re-programmed with the extended software (v2-50.hex) . If you do not wish to change the software you are using at present you will soon be able to get a programmed IC2 from the BATC Shop with the latest version of the software already programmed. Please specify the v2-50 version when ordering.

The code for the DigiLite itself is unchanged so there is no need to change it unless you plan to use the card option.

The 10 pin male header (JP1) is already on the DigiLite pcbs so only a 10 way female plug and ribbon cable will be needed to connect to the card reader interface board. There are a few components on the interface board, but they are simply pull-up resistors and a decoupling capacitor, otherwise it is simply joining the ribbon cable.

DTS1010 Build A3 CIRCUIT DIAGRAM.

Note the unusual numbering sequence of the SD card socket

- Resistor values are nominal 33K but can be from 22K to 68K.

- J95 is the PIC programming connector, if required.

- J93 and J94 are joining points on an optional USB cable.

- Ground is at JP91 pin 7.

Referred to as the DTS1010 there are a number of points to be made about this add-on.

(It is essential to read full details in the DT1010 pdf on the DigiLite website before commencing a build).

You can cram about 40 minutes of transmission onto a 2GB card. It needs to be a 2GB(no larger) SD card (not SDHC) and with FAT16 format only. Colin G4KLB who made the boards shown in the pictures says that if you purchase the Verbatim 2GB SD card it is already formatted in FAT16. Details of how to format an SD card are in the pdf file.

The file name is critical and must follow a specific format for the software to deal with it. The file must be in the main directory of the card (not inside a folder) and must be named DT_*****.#FX where # is the Symbol Rate (see tables below),F is the FEC setting and X is FEC on/off. ***** can be any valid characters ie:E.g. DT_SHACK.431 = SR4000, FEC 3/4, 1 means the FEC needs to be applied. See details below.

Files will be played in alphabetical order, so remember that when naming them.

Transport Stream files are generated by the program 'DigiLite TS Generator' which processes the mpg files made by WinTV or GB PVR.

In the photo you can see a small press-button switch. This enables you to step through the files on the SD card.

There is a also a 'card inserted' switch built in the card reader socket, so you only need to add one if you don’t want to remove the card (if it is inside a box for example) this is best wired to the card reader PCB.

The pcb is about 62mm x 37mm, if preferred it is possible to wire directly from the DigiLite pcb to the SD card holder via the 10 way plug and fit the three components onto the plug itself thus avoiding the need for the pcb.

Carousel Mode

Holding down the button for five seconds selects Carousel Mode, where all valid files are transmitted in sequence in alphabetical order.

After the last file in alphabetical order has been transmitted, the first file in alphabetical order will be transmitted again.

Carousel Mode may be automatically selected by putting a file named DT_.CAR on the card. This file will be detected when the card is inserted.

There will be a short delay before a file is transmitted while the file is being prepared. This is proportional to the size of the file.

There will be a glitch in transmission at the end of the each file.

If the button is pressed when Carousel Mode is active, Carousel Mode is de-activated and the next file in alphabetical order is transmitted repeatedly.

If the main part of the file name ends with @ (e.g. DT_F12@.431) it will be skipped in Carousel Mode. If such a file is being transmitted when Carousel Mode is activated manually, the next file in alphabetical order without an @ will be transmitted immediately.

The interface board. Cutaway allows access to presets on main board.

The connections on the SD card PCB marked GWR are not part of the SD card circuit but are provided to connect an optional panel mount USB socket (Farnell 122-9686) You have to cut the USB lead that plugs into the FT module ( GWR stands for Green White Red, which seems to be standard colours for USB wires) If you don’t need a panel USB socket this can be ignored.

A suitable SD card socket is Farnell 918-6158

The pcb tracking.

The etched board ready to populate

There are several pdf downloads available at the DigiLite website which contain 1:1 and mirror images of the tracking. Final size should be 61.9mm x 37.1mm

The following characters are used to indicate the symbol rate (# in the section above):

1000 1, 1333 B, 1500 C, 1667 D, 2000 2, 2500 H, 3000 3, 4000 4, 4167 T, 5000 5, 6000 6, 6250, Y 8000 8

DigiLite TS files must reside in the root folder (directory) of the SD card. Valid file names are of the form DT_ABCDE.#FX ABCDE may be any valid Windows characters

# indicates the symbol rate (SR) at which the file must be transmitted.

F indicates the FEC.

X = 1 indicates that the FEC needs to be applied. X = 0 indicates that no further processing is needed. This is determined by the FEC setting in DigiLite Config when the file is converted.

E.g. DT_SHACK.431 = SR4000, FEC 3/4, the FEC needs to be applied.

The stepper button must have a 1k5 resistor in series.

As I said earlier, this is only a brief overview of the project, please download and read the full documentation.

I know that Brian G4EWJ has put a lot of time into getting this software to this high standard and I would like to register my thanks to him for releasing the software and his pcb design information and to Colin G4KLB for supplying me with the photos.

All required software and pdfs can be found at http://www.g8ajn.tv/dlhardware3.html

The G8BYI Digilite VCO Controller

by Dave Kenward, G8AJN

This is a full-function DigiLite Controller designed by Richard Burrows G8BYI< using the 16F628A 18pin SMD.

In Circuit Serial Programming (ICSP) allows you to change the software without the need to remove the chip. Header JP3 is used for this function, more details later in this article.

The 470 ohms and 10k dividers reduce the maximum voltage from the 5v PIC chip to prevent damage to the ADF4360- 5 which runs on 3.3v. JP1 is the 3 pin connector that connects the PICboard to the VCO board where the original PIC chip sat. These connections should be kept to an absolute minimum length. Richard recommends using 3 feed-through capacitors to get into the VCO can if separate to the controller board, but ideally keep the BYI board and VCO in the same fully enclosed can. Screened wires may be an alternative to the rather expensive feed-though 1000pF capacitors. However you decide to connect it, keep the leads short.

The VCO requires 8v from a regulator(or the one on the DigiLite) this can feed into the 5v regulator on the board. A heatsink on the 5v regulator should not be necessary as the BYI board uses only 40mA. Because the chip is Surface Mount type it is necessary to program the software into it either before fitting or using In Circuit Serial Programming (ICSP) after it has been soldered onto the board.

Please note: R13 and C6 are not required.

Richard has now set software to display on a 2x16 or a 2x20 lcd. It uses a push button for the Mode change switch to change between 100KHz stepped tuning mode or one of 24 pre-set channels. The other two push buttons set the frequency as up/down buttons, when you hold the buttons while in Tune mode the frequency steps through faster to speed up getting to the frequency you want.

The unit remembers the last frequency used and comes back on at that frequency. The ADF4360-5 VCO chip on the Ultram board uses a 24bit latch for data entry, so the 24bit long word needs to be built up from three 8-bit words.

Programming notes

‘DWORD usage - lowbytes=1st 8bits byte1=2nd 8bits, byte2=3rd 8bits ‘

setfreq

- ‘reg A= 0-31 max 5bit

- ‘reg B= 0-2096986 13bit max

- ‘1240MHz= N=12400 b=387 a=16 P=32

- ‘1320Mhz= N=13200 B=412 a=16 (p=32 prescaler is in function register)

- ‘div=bp+a for 100khz steps this is freq as well which is convenient

lcd display calc

- ‘Areg=areg+1 :If Areg >32 Then Inc Breg: Areg=0

- ‘n=b*p+a ‘ N=(32*Breg)+Areg :’shows freq. on lcd ‘Initial Freq as defined for 100khz steps ‘

Other adf4360-5 chip Parameters that are set

- ‘ PFD Freq 100Khz

- ‘ Ref Freq 10MHz

- ‘ RF Prescaler 32/33

- ‘ Internal /2 not selected

- ‘ Output /2 not selected

- ‘ CP Gain=0Current setting 2.5mA

- ‘ RF PD Polarity Positive

- ‘ Charge pump active

- ‘ Counter Reset Disabled

- ‘ Lock detect Precision=3

- ‘ Band Select Clock Divider Value=8

- ‘ O/P power -6dbm

- ‘ Muxout = digital lock detect

- ‘ Core Power 10mA

- ‘ Mute till lock enabled

The printed circuit board

Shown enlarged here, the actual size is 49mm x 49mm. Double sided but with only two links on the underside track, the rest is earth plane. R14 to R19 are links (0 ohm 1206) unless you are using the 5 LEDs of the Simple version (see DigiLite website) where they are the voltage droppers for the LEDs themselves.

There are three main latches in this device, called R ,Control and N latches. There are many other parameters that can be set by the user, but here we are using preset values supplied by Analog Devices in software they supply on their website. Please refer there for further technical information. The latches must be addressed in the correct order, R then Control then N.

The G8BYI Proton+ Basic Code can be downloaded from the batc website. (The Hex file is also available for download).

Please respect Richards copyright on this software and only use it for your own build, do not re-publish it anywhere modified or without the copyright message.

A pre-programmed smd chip and an inexpensive commercially manufactured pcb is now available from the BATC shop. The homebrew pcb is shown here. If making it yourself you can just etch the top side and leave the lower side as earth plane and use wires for the link required underneath. The commercially made boards are ready drilled for connectors and using SMD components including the PIC chip.

Initial home brew test board to check layout and software.

Because the chip is SMD it might be necessary to program the software into it whilst it is in circuit. The safest way to program the PIC is with the board unpopulated.To do this you will need to fit the IC and the 5 way header first. Then with a standard PIC programmer board but using the header JP3 with the PP,VCC,GND,RB6(PGC),RB7(PGD) connections instead of the ZIF socket. On version 1.1 boards you temporarily link the pin 1 of JP3(Vcc ) connection to pin 14 of the IC. Disconnect one end of C1. On later versions the link and C1 lift will not be necesary. Do not apply any dc power to the G8BYI add-on board except that which the programmer supplies via the JP3 .Run the ICSP programming software for the 16F628A with nothing plugged into the ZIF and only the 5 wire link connected from JP3 with a 5 wire plug to the ICSP header.

Parts List: Please note: R13 and C6 are not used.

Select ICSP mode for the 16F628A using the ‘Disable LVP option’ (or fuse) then run the program as usual. Do not try to program with C1 connected as it will prevent the ‘chip detect ‘ function of the programmer from working. Here is the principle behind in-circuit programming. If you do not have a programmer please enquire about getting an IC chip already programmed at the BATC shop. http://www.batc.org.uk/shop/kits

The Ultram VCO board and connections for the controller. The PIC chip should be removed first. The MMIC can be left in circuit if preferred . The buffered output from the MMIC might be useful for other projects.

Connections for the blue/white 20 character display. The 100R is a LED current limiter (brightness) and can be changed to suit the users requirements. The 10k pot is the contrast control.

There are currently two versions of the G8BYI add-on board, versions 1.1 and 1.2

The original one (marked as QT110521) is intended to use a pre-programmed PIC prior to fitting. If you wish to change the software at a later date a link between pin 1 on JP3 and IC1 Pin 14 can be used but the electrolytic decoupler C1 should be disconnected at one end to allow the IC to be recognised by the programmer. Connect a cable from the header on your programmer to the header JP3 and select ICSP(or ICP) in the programmer software. Do not apply any separate volts to the board, only that which the programmer generates. Of course remove the wire and re-solder the capacitor when finished.

Version 1.1 circuit and PCB Version 1.2 circuit and PCB

NB:JP1 Clk and LE labels are transposed, see circuit

A modified board has now been produced, unremarkably named version 1.2, which has an isolated supply line via added diode D2 and C9 to allow reprogramming of the PIC without requiring the link to be inserted and the capacitor removed. In an attempt to make life as difficult as possible the connections on JP2 have changed and the regulator U1 has turned 180 degrees and the labels on JP3 are misprinted!

Download software and see corrections and updates on the DigiLite website in the Hardware section. Thanks to Richard G8BYI for allowing full details of the software to be published for the benefit of all.

DigiLite website: www.g8ajn.tv/dlindex.html

Using the DigiLite on 70cm

by John O’Loughlin and Gary Grivna K0GX

When we began to put together a 70cms version of the DigiLite it soon became obvious that there was no accurate setting up procedure so we decided to look into the various options and tried to compare the results to see which was the most accurate and which was the simplest. Here are the items we addressed and results we achieved in building a 70cm version of the DigiLite.

The AD8346 modulator was replaced with an AD8345. Whilst the AD8346 covers 800MHz to 2.5GHz, to reach lower frequencies the AD8345 should be used. This device covers from 140MHz to 800MHz putting the 436MHz band in the centre of its range.

A UK build of the 70cm DigiLite by G4KLB

N.B. Because the AD8345 has a much higher RF output it has an exposed pad on the bottom that improves heat dissipation when it is soldered to the circuit board. Since the DigiLite board was designed originally to be used on 23cms it has no provision for this pad, the junction-to-air thermal impedance is three times higher than when it is soldered to a ground plane. 70cm boards should have good air flow and improper adjustment could increase the RF output causing more heat.

LO input

AD8345 typical input is -2dbm. The Ultram output measured 10dbm, so with the 12db attenuator in the Digilite it’s a match!

RF output

AD8345 typical output is about 0dbm. The MAR6 P1db is so close to that one may as well remove it and its input attenuator and run the AD8345 straight out. We replaced the MAR6 with a Sirenza SGA-5589. We increased its input attenuator loss by changing the resistors to 127 ohms shunt, 46 ohms series setting up the SGA-5589 for 15dbm out. The more standard values of 120 and 47 ohms would work well too. Improvement of the SGA-5589 performance could probably be made by someone willing to put in the effort to optimize the surrounding part values. The new output actually measured 14.8 dbm, enough to drive an RA60H4047 to 40 watts.

I-Q drive

The AD8345 drive and bias voltages are much lower. Lowering the signal with the pots only would result in an unbalance of the differential input to the AD8345. We changed resistors in the voltage dividers to the AD8345 inputs, R15, R18, R22, R25 to 422 ohms. The voltage at the AD828 outputs will be the same as with the AD8346 therefore the set-up procedure will be the same as the 23cm version.

Miscellaneous

Several RF coupling caps were increased too. We have also used the SGA5589 on the 23cm DigiLite to get higher output and for the preamp before the RA18H1213 power amp. We had a couple failures that we suspect were due to operating without a load on the SGA5589.

Here are the new values of the parts we changed: R15, R18, R22, R25 = 422 Ohms R34 = 47 Ohms R36, R37 = 120 Ohms C30, C31, C28, C29 = 270pF IC4 = AD8345 U5 = SGA-5589Z (e.g.RFBay on Ebay) R41= remove R26=68 Ohms

Please note: The authors of this article reside in the US and have a wider 70cm band available than we do in the UK. With our band limitations we can only use 1Ms/s.

Refer to the chart to select correct components for the Nyquist filter.

Set-up Procedures

When K0GX and I were researching our first 23 cm DigiLite the concept of setting it up by observing the satellite receiver quality meter sounded a little hit or miss. However we were able to find an L band Spectrum Analyser at a very good price and incorporated it into our set-up method. The AD8346 datasheet specifies that the signals at the I and Q inputs should have an AC swing from 0.7V to1.4V. Examining the DigiLite modulator circuit shows the signals at the AD828 op amp outputs will be twice that, 1.4V to 3.4V. By using an oscilloscope that signal waveform can be easily achieved by adjusting the BIAS and LEVEL pots.

Further circuit analysis determined the main effect of the BIAS pots is controlling the balance of the differential inputs to the AD8346. That controls the amount of carrier (LO) leaking through the balanced modulators to the RF output. The LO leakage can be eliminated by adjusting the BIAS pots while observing the Spectrum Analyser. Setting up with these methods resulted in 99% quality, the highest the receiver displays.

Dave G8AJN assured me in email conversations that it really is possible to get a usable signal using just the satellite receiver ‘quality’ meter, so I starting wondering how that could be. We set-up the DigiLite on the bench and observed the results of adjusting the pots on an oscilloscope, a spectrum analyser, a satellite receiver and a digital voltmeter.

The voltage affecting the differential balance of the I-Q drives can be measured on the LEVEL pot from the wiper to the TLE2426 end. With the LO nulled out, the voltage measured about 8mV with the DVM. When the BIAS was adjusted for 0V the LO leakage was about -50db from the signal. The bias was then adjusted until the quality meter reading decreased to 90%. At that point the voltage was 150mV and the LO leakage was -15db under the signal. This demonstrates that the DigiLite tolerates large offsets and that the BIAS pots can be set for a very acceptable LO leakage with just a DVM.

We also checked the DigiLite’s tolerance of LEVEL pot misadjustment. The nominal peak to peak level is 2V. The Q LEVEL was adjusted from 2.5 Vpp to 1.5 Vpp with no change in the 99% quality reading. The quality fell off the cliff to 0% at about 1.3 Vpp. The same results were seen when adjusting the I LEVEL. Again this demonstrates that the DigiLite tolerates large offsets.

These tests show setting up the Digilite with only a DVM gives results very close to using an oscilloscope and spectrum analyser.

The I and Q signals are generated by logic outputs switching from common to 5V, therefore the level of the signals leaving the Nyquist filter will be the same, within a few percent, on all units. Because their input is consistent the LEVEL pots could be adjusted to a standard ratio or even replaced by fixed resistors, 68 ohms from B1 to B2 and 33 ohms on the other side. Setting the pots by measuring the resistance may not be accurate because of the influence of the surrounding components. I have worked out a way to set the LEVEL pots with the DVM by measuring voltages. If you would like a detailed description of the bias arrangements see the last part of this article.

A modified circuit diagram for 70cms is available for download at www.g8ajn.tv/dlindex.html

Digital Voltmeter Set-up Procedure

Using the DigiLite Config Program, set the Test Mode to IN PHASE.

* Connect the negative lead of DVM to the TLE2426 end of the LEVEL pot (B2) and the positive lead to the other end. Adjust the BIAS pot for a reading of 200mV.

* Measure the voltage from the LEVEL pot wiper to the end connected to the TLE2426. Adjust the LEVEL pot for 100 mV. (sets the drive level)

Measure the voltage from the LEVEL pot wiper (B1) to the end connected to the TLE2426(B2).

Adjust the BIAS pot for 0 mV. (sets the bias/balance)

Repeat for the other channel. (* If LEVEL pots are replaced with resistors the first 2 steps * will not be required.)

Using an oscilloscope is a more accurate method of setting the level if you happen to have access to one.Connect the oscilloscope to IC3 pin 7. Adjust LEVEL pot R23 and BIAS pot R29 for a 2 volt peak to peak sine wave signal swinging from 1.4 VDC to 3.4 VDC. Connect the oscilloscope to IC3 pin1. Adjust LEVEL pot R16 and BIAS pot R30 for the same waveform. Then perform the last step in the DVM procedure to zero the bias LO input.

70cm Software

by Richard G8BYI

Settings

If WinTV6 does not seem to operate happily at the low data rate use the GBPVR program instead. This might be useful if you wish to use one DigiLite on 70cm and another on 23cm as the 23cm can be set up using WinTV6. To set up PVR for 2MS/s, go into GBPVR’s Config Utility and edit the settings for Custom1 Quality.

Video Resolution : PAL 352/576 Bit Rate 1500 Constant Audio Bit Rate 192 Audio Sample Rate 48kHz Save and exit.

1500 is actually too fast for 2MS/s, but GBPVR won’t allow a lower setting. To get around this, you need to find GBPVR’s install directory and edit DIRECT.INI Look for the section [SETUP-Custom1 Quality]. Change the BitRate to 1350. Save and exit.

Having done this, if you try to edit the Custom1 Quality settings with GBPVR, Config will crash.

How and why the DVM set-up procedure works.

I will refer to the Q signal in this discussion, the I signal operation is the same. The bias at Q+ and Q- should be 1.2 volts for an AD8346. The voltage at the top of R12 and R14 should be double that, 2.4V. The 70cm version has different divider resistors to accommodate the AD8345’s lower bias voltage so the same voltage is required at the top of its dividers.

The centre voltage of the signal at Q, the input to the Nyquist filter, is halfway between the power rails, about 2.5V. If the BIAS pot R30 is adjusted so U4 puts out the same voltage as the Nyquist filter your DigiLite will be close to proper bias adjustment, but there are still a few other factors to be considered.

When you raise or lower the BIAS, the difference between the U4 voltage and the filter’s centre voltage will cause current in the path highlighted in yellow. The voltage drop across the LEVEL pot R16, from the wiper to the C25 end, will cause the bias voltage at Q- to be different than at Q+. Thus by adjusting the U4 voltage a little bit higher or lower you can change the balance of the differential input to the AD8345 or AD8346 and control the LO leakage.

Q- and Q+ drive a balanced modulator. R12 draws current to ground causing the voltage at the wiper of the BIAS pot to be a bit lower than the filter output. As a result, the bias at the dividers is about 2.4V when the BIAS pot is properly set.

Note: If you were to install an AD8345 without changing the divider resistors you would either operate at too high a bias or the balance would be way off centre.

After the LO leakage was nulled out using a spectrum analyser the voltage from the wiper of the LEVEL pot R16 to the C25 end was found to be < 10 mV. Setting that voltage down to zero caused only a slight amount of LO leakage. Also the Digilite still puts out 90% quality with 150 mV of offset. This explains why setting the bias to zero with the DVM will reduce the LO to an acceptable level.

Setting the test mode to IN PHASE sends a 50-50 square wave into the filters for consistent centre voltage.

The peak to peak voltage of the I and Q signals were first set to the proper levels with an oscilloscope. The position of the wiper was then calculated by measuring the Vpp in and out of the LEVEL pot. It was found to be 67% or 68% on both a 70cm and a 23cm DigiLite.

The DVM level setting procedure begins by setting the BIAS pot far enough off centre to put 200mV across the LEVEL pot. The voltage from the wiper to the end is set to 100mV, the voltage measured on the properly set units. This may seem to be different than the 68% ratio just mentioned but the current through R12 explains the apparent error. This technique will set the level well within the range that will give good quality.

DigiLite kits

Table of Contents

Welcome

DigiLite System Overview

DigiLite System Outline Details

Recording program

Conversion program

Serialiser

Modulator

Configuration

The Digilite Project - Part 1

Background

DigiLite

DigiLite System Outline

Windows PC

Recording program

Conversion program

Serialiser

Modulator

Configuration

DigiLite Transmit User Guide

Finding a Captured Video File

Status Messages

User Control

Normal Operation

Input File

PCR Lag

Packets Out

Serialiser

Boot

Re-sync

DigiLite Config User Guide

First Run

Communications

MPEG Input

Capture Device

Input Method

Transport Stream

Symbol Rate

FEC

FEC on PC / Serialiser

TS Delay

Buffer Delay

Test Mode

Channel Info

PIDs

Channel Name

Programme Name

EPG Info

Saving Settings

Windows Registry

DigiLite Serialiser User Guide

Power Supply

LED Indications

10 Pin Header

Description of the circuit diagram.

What you will need

Hardware

A DigiLite Board

Software

Where to begin

GBPVR Program

GBPVR Main Menu

And Finally

The Digilite Project - Part 2

The hardware

Hardware Check list

Hauppage PVR CARD

The Local Oscillator

THE SOFTWARE

A check list

The USB panel

FT223 2H

FT2232H USB Module Installation

Preparation

Editing the Configuration

Programming the Configuration

Finding which COM ports have been assigned

The Serialiser

PERSONAL VIDEO RECORDER

WIN TV PVR

GB_PVR

GBPVR CONFIG

GBPVR Program

DigiLite Transmit

Some initial DC voltage settings

Satellite Receiver

To get on-air

Parts List

The Digilite Project - Part 3

Additions to the Parts List

Constructional notes

All versions

Initial check list

Who needs a Spectrum Analyser anyway?

Running DigiLite on 70cm

Digilite: the future

Simple tuning add-on

Adapting the ULTRAM local oscillator

Help! My DigiLite does not work!

A Card Reader for the DigiLite board

Carousel Mode

The G8BYI Digilite VCO Controller

Programming notes

setfreq

lcd display calc

Other adf4360-5 chip Parameters that are set

The printed circuit board

Using the DigiLite on 70cm

LO input

RF output

I-Q drive

Miscellaneous

Set-up Procedures

Digital Voltmeter Set-up Procedure

70cm Software

Settings

How and why the DVM set-up procedure works.

DigiLite kits