BATC Portsdown digital ATV transmitter project

To be QRV on different HAM bands the "BATC" has started a project. Through the club you can buy some circuit boards you have to fill with parts you need to buy yourself. You also need a raspberry Pi 3, a touch screen, and ofcourse all the parts to get to satisfying end of the project.
This project gives you a low power DATV transmitter. Can be used stand-alone for in the field.
Edit: As of the end of 2018 the modulator board/oscillator will be absolete, new version will be with a "Lime-SDRmini" with the outputswitch/band decoder after it..

 

  

Picture on the left what you need and can/could be bought through the BATC.
Pre build filter modulator board.
Local oscillator board.
GPIO breakout board.
4/8 band decoder board.
4/8 band output switch board.
Sandisk micro SD card with software for Raspberry Pi.
eventually a "Easycap Video Capture device"

Buy elsewere:
Raspberry Pi 3.
Waveshare 3,5" or Pi 7" touchscreen.
ADF 4351 oscillator board. (ebay)
40-pin GPIO stacking header.
Buck converters as switched power supply`s (ebay)
Attenuator board. (ebay)
All parts to solder on the boards.
All hardware to come to a good end.

To order through the BATC you need to be a member. You get a magazine in PDF as well.
 
When you installed the software, installed the touchscreen you already can use the Pi to make a DATV signal in UGLY mode. This mode is to "ugly" to put on air and can only be used as a test signal across the shack. The signal transmits on 437Mhz, but can be adjusted in the software.

The RF output switch and 4 band decoder are put together. But in the meantime I already ordered the 8 band versions. This gives the opportunity to switch between 8 bands, so you can use transverters for higher frequencies. Here in PA country the 70/145Mhz can`t be used due to band limitations.

To receive in ugly mode I also bought the Minitiouner V2.0 board+tuner. So I can test DATV reception, instead of using a external home SAT receiver with rx converters.

Some boards and the Pi needs power. The Pi needs 5.1Volt. RF switch 12Volt. LO filter/modulator 13.8V, ADF4351 needs 5 volt.  These volts are made using a toroid transformer rectified and fed into 4 small switched power supplies (buck converters). These have the size of 2x4cm and can be bought through Ebay for €1.50/piece. I connected these and probed them using a spectrum analyser. Some spikes on HF to 30Mhz. So I made a casing of double side circuit board to put these in. Used feedthrough caps and ferrite coils on the in/output for extra filtering. Nothing seen on the SA with lid colsed.
The green stuff you see is polyurathane lacquer for protection.


 

While looking for these buck converters I stumbled across some digital voltmeters. For the price of these I can`t even buy the parts and make time free to build them. For €1/piece I can put these small LED voltmeters on each output permanently, just because I can.
Size is 31x12mm.

to be continued.

April 2019