RB-TV on the BATC DTX1 Convention for Amateur Television 2015 (CAT15) over the weekend of 5th and 6th of September at Finningley Amateur Radio Club. A presentation by Laurence M0LDZ.

Integrated MPEG2 encoder & RB The DTX1 accept PAL or NTSC Analogue Video and Stereo Sound, and convert this to Transport Stream. First, the video signal is fed to an ADC chip, which produces an 8 bit output at 27M Bytes/Sec. We compress this signal using an MPEG2 Encoder chip – but below 1Mb/s it’s unusable. How do we get round this problem for RB-TV? A similar process is applied to the audio channels and the two feeds are merged. This adds to the bandwidth generated by the video.

MPEG Compression Chip MB86391

Digital Modulation – the Hard Bit We add control packets to the audio and video - now we have a transport stream, but this is not yet encoded as per DVB-S Standard, which is very complicated. The solution – a Field Programmable Gate Array (FPGA) takes the transport stream and encodes the signal to the DVB-S standard, producing digital Quadrature outputs.

Complete DTX1 Board

A Subtle Feature Exploited The DTX1 is a variant of a Antennair’s DVB-T product. This was designed with a 2nd video/audio encoder stage option – so the FPGA contains a 2 Channel Multiplexer, and the PCB brings out the spare input channel on a 34 Way connector. (Was pins, but is a socket on DTX1). This left open the possibility of future add-on card with different compression e.g. H.264 Since the Raspberry Pi board has a camera input and H.264 Compression in Hardware, we decided to make a Transport Stream Dock PCB!

Original TS_Dock Schematic

Early Issue with TS_Dock PCB

New TS_Dock PCB and the RPi

Wide Range Digital Synth ADF4350 – 137.5 to 4400 MHz

Analog Devices Modulator ADL5375

Ongoing Work on DTX1 Frequency Range Removing the Harmonic Filter on the Synth Output – allows useful signal output to 2.45GHz with re-programming (output is down ~7dB) Harmonics at lower frequencies slightly worse but close-in performance is still excellent. External filters should be used. Re-programming the Synthesiser at the low end already extends coverage down to 2 metre band, despite modulator IC’s quoted lower limit! Beta release firmware available NOW at CAT15.

Thanks and Acknowledgements Hardware design of TS_Dock PCB by yours truly - Laurence, M0LDZ DTX1 Firmware design by Carl M0ICS Raspberry Pi firmware for sending the H.264 Stream on to the TS_Dock parallel port by Evariste, F5OEO Testing above 2GHz by Noel G8GTZ. All those here today & online for watching!

A Compact Solution for RB DATV BATC DTX1 Encoder / Modulator