M0DTS.co.uk

 

 

Digital ATV Project

 

These are my findings with

The Poor Man's DATV Transmitter by F4DAY

 

 

Since reading an issue of CQ-TV magazine i have been wanting to try and build the Poor Man's Digital ATV Transmitter. This is a design by F4DAY for a relatively cheap way to transmit low data rate Digtal Television.

This is the only reasonable alternative to the AGAF and SR-Systems transmitters costing well over £600 now!

 

The main parts of the transmitter are: the Serializer, Buffer / Nyquist filter, Modulator and also the JTAG programmer for programming the Altera chip.

 

The serializer is built just as the design using double sided pcb, i had to use a standard size oscillator as smd version was not available.

ser1ser2

The serializer is connected to the PC's parallel port to provide the IQ video stream to be sent to the modulator.

 

 

For now i'm only using the buffer and Nyquist filter on the original modulator board, i have just put in the two 1.5k resistors as specified in the design to give best results, these may have to be adjusted for my system to work properly...

buf1 buf2

 

The original design was to use a modulator and oscillator at 70MHz to be used to mix up to the main amateur tv bands, but i thought the analog devices AD8346 IC was the easier option to modulate directly on 23 or 13cm.

The modulator board i have made up is from a design by F1HPR

mod1 mod2

 

Tests on the Sideband suppresion and LO Cancellation and the modulator appears to work reasonably well at 23cm...

I have not yet tried 13cm...

lsbusb

carrierdigital

 

 

The satellite receiver i am using is a new one to me, a Comag SL65/12 which covers the required symbol rate of 1.024 MS/s and SCPC mode (Single Channel per Carrier) but SCPC is not mentioned in the manual...

I setup a new satellite called '23cm DATV' with settings to be LO of 10GHz and have setup a transponder on 11.280GHz with Symbol rate of 1024Ks/s and FEC of 1/2.

 

This is a X-Y plot of the I-Q data going into the modulator, at this point should i be able to see all of the 16 points in each corner or just a dot where thery are meant to merge ??

constellation

 

 

UPDATE 10th Dec 2007

 

Today i managed to get the transmitter to work .. WOW!

The problem turned out to be the PC that was running the readpsk program, i can not explain why but i have tried a third PC and it fired up first time. The new pc has an ASRock motherboard compared with the other that had a GiGabyte one. i have also tried one laptop but it could not find it's own parallel port in dos?!

Here is a small clip of my first test transmission!

M0DTS Digital ATV Test

 

I have also used my SkyStar2 card in my pc to decode the trasnmission with excellent results even though it is only supposed to go down to 2MS/s !

 

Now to find an easy way to get the video files to the correct format, the current method takes three steps..

Mpeg2 to DVB transport stream (1024kbps) MainConcept Reference

Or this can be done with VLC

Modify transport stream to add Channel Name TS2TS.exe by F1FAU ( will work fine without )

Convert Transport stream to IQ stream for transmitter TS188ToIQ.exe by F5OEO

 

see below for some video's of how this is done.

 

 

 

Update 15th Dec 2007

 

Readpsk C Files Dos

The computer uses a program in DOS which needs to be compiled from C code, the original code did not work for me but i managed to to get it to compile and work with a few modifications to make it easier to use.

The dos version compiles with DJGPP compiler that F4DAY Suggests. If you use DJGPP compiler you need to select C and C++ at zip picker.

I have created new versions of the code for DOS to automatically find the filesize, no need to re-compile for different files readpsk_dos.c

 

& Linux

I have modified a version to run on Linux too, This gets around the small file capabilities of running in DOS (32MB?).

I can now transmit up to 20 minute long AV stream which is ~300MB (limited by pc memory) readpsk_linux.c

 

 

 

Update 23rd Dec 2007

Today i made my first 1-way Digital ATV Contact with Clive G4FVP.

We ran tests on 1280MHz using a power level of around 3Watts peak on both Analogue and Digital over a path of 19KM.

The results confirmed that the digital was much better for weak signals at this low symbol rate of 1024.

Here are some screenshots of the results.

 

Analogue Transmitted____________________Analogue Received

analogue_origanalogue rx

 

 

Digital Transmitted______________________Digital Received

digital_origdigital_rx

 

 

 

 

Small update Dec 2008

On request i have made up two short videos showing how to create the stream file to send to the serialiser using VLC and ts188toIQ.exe

First you need to pre-record a video ready to be encoded, preferably 352x288 resolution.

1: Using VideoLAN to convert your pre-recorded video clip into MPEG2 Transport stream.

2: Using ts188toIQ to add the DVB formating to the transport stream file.

Only one of the output files generated by ts188toIQ program is required, this is the *****.tsIQ file.

The readpsk program (once it has been compiled to an executable) is then used to send the *.tsIQ file to the transmitter through the parallel port of your PC.

 

 

M0DTS.CO.UK
Updated 23 May 2009