QRP on WB transponder?

Latest News and Discussion about the use of the DATV transponder on Es'hail-2
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dh2va
Posts: 27
Joined: Tue Oct 09, 2018 10:00 am

QRP on WB transponder?

Post by dh2va » Mon May 11, 2020 10:51 am

A question to the experts:
What is the practical (demonstrated) limit in terms of QRP operation on DVB-S2? More specifically, I have a (XYL-limited) 88cm dish and a working Portsdown, which is in the process of being upgraded to V2019 (limeSDR mini). I know that DVB-S2, QPSK with FEC 1/2 should have little CNR requirements and combine this with 66kS rate would require even less power (5W according to https://wiki.batc.org.uk/Transmitting_O ... TV_signals ?).
I am aware that 66kS with FEC 1/2 will be likely a horrible picture but is is enough for a testcard?

73s Achim

g0mjw
Posts: 1168
Joined: Sat Sep 20, 2014 9:15 am

Re: QRP on WB transponder?

Post by g0mjw » Wed May 13, 2020 2:30 pm

Yes it is, I used 35ks QPSK and 200mW to send an rather poor quality image over the satellite. This was with one of G0MRFs driver amplifiers. I am cheating though as it is a 2.4m dish so about the same as you running a couple of watts. Regularly can send video with 1W or less. 66ks QPSK 1/4 rate coding, with no audio should work fine, but your system should be a lot more capable than that.

Mike

dh2va
Posts: 27
Joined: Tue Oct 09, 2018 10:00 am

Re: QRP on WB transponder?

Post by dh2va » Thu May 14, 2020 6:39 am

Mike,
thank you for the reply, I really appreciate it. It's a kind of stealth attempt to get DATV on the air without making either XYL nor the neighbours suspicious. I really would enjoy a larger dish but the 88cm is completely fine with everybody ('What programmes are you watching?') despite the POTY having replaced the LNB.
Will actually refit my Portsdown to 2020 after checking the BATC wiki.. big thank you to everybody involved.

73s Achim

g0mjw
Posts: 1168
Joined: Sat Sep 20, 2014 9:15 am

Re: QRP on WB transponder?

Post by g0mjw » Thu May 14, 2020 1:23 pm

I understand, you can choose the XYL but not the neighbours. You just need a lot more power with a smaller dish. QO100 downlink is strong and above 1.2m there is not a lot to be gained. You just see more of the transponder noise floor.

Mike

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