Using the Portsdown TX for the Contest

Discussion about this major DATV Project. See https://wiki.batc.org.uk/The_Portsdown_Transmitter
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G8GKQ
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Using the Portsdown TX for the Contest

Post by G8GKQ » Thu Jun 06, 2019 2:47 pm

The Portsdown transmitter has been designed to make contest operation easy. Here are some suggestions:

Remember to enter your planned locator into the system before you go out portable (Menu 3, Set Call Loc & PIDs, Locator). This will then display on the caption and enable you to calculate the bearings of other stations easily (Menu 2, Locator Bearings) on the day.

Choose your numbers for each band (and for each site if you are roving) and note them down. Enter them in the Portsdown for each band (Menu 3, Set Band Details). Also make sure that you have the correct Lime Gain set for each band.

If you are using a Lime SDR, please test the modes that you plan to use before the weekend; I know that some do not work. With the latest software (201905090) I have tested the following H264 modes which seem to work reliably with the internally generated Contest Numbers:
  • DVB-S2 QPSK 333KS FEC 1/2
  • DVB-S2 QPSK 333KS FEC 9/10
  • DVB-S2 QPSK 125KS FEC 1/2
  • DVB-S2 QPSK 125KS FEC 9/10
  • DVB-S2 QPSK 1000KS FEC 1/2
  • DVB-S2 QPSK 1000KS FEC 9/10
  • DVB-S 333KS FEC 1/2
  • DVB-S 333KS FEC 7/8
  • DVB-S 125KS FEC 1/2
  • DVB-S 125KS FEC 7/8
  • DVB-S 1000KS FEC 1/2
  • DVB-S 1000KS FEC 7/8
FEC 1/3 and FEC 1/4 do not seem to work with the Contest Numbers at present. If you are using a camera as the video source, please check what works for you before the weekend. It is always a good idea to try to monitor your transmitted signal.

I think that DVB-S2 QPSK 333KS FEC 1/2 is probably the most robust mode for the contest. Although 125KS has about 4 dB more punch, the signal needs to be constant for longer, so any fading may prevent a lock. In deep fast fading, I think that 1000KS could be better than 333KS. DVB-S2 will give a 2 dB improvement over DVB-S.

Good luck in the contest!

Dave, G8GKQ
Attachments
Contest Numbers.JPG
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