DVB-S2 On-air Tests

[G8GKQ]

Last week Charles G4GUO, Noel G8GTZ and myself conducted some on-air comparisons of H264 DVB-S and DVB-S2 at various settings. We used a near-LOS 44 km path between Worthing and Portsdown Hill, reducing the power of the signals at 437 MHz until the receivers ceased to display moving pictures. Power was reduced in 1 dB steps, and there was at least 1 db atmospheric variation during the test period, so the results below are indicative, not absolute!

We also tested DVB-S2 with and without Pilot symbols enabled and could not demonstrate a reproducible difference. We were unable to test 333KS DVB-S2 due to equipment problems on the day. I used both MiniTioune (0.5 beta) and a commercial satellite receiver - the results were similar where both receivers were capable of receiving the transmitted mode.

Code: Select all

Mode                        Relative Level Required (dB) 

DVB-S QPSK 1/2 FEC 2 MS      0     
DVB-S QPSK 7/8 FEC 2 MS     +2
  
DVB-S2 QPSK 1/2 FEC 2 MS    -3    
DVB-S2 QPSK 8/9 FEC 2 MS    +1    
DVB-S2 QPSK 1/4 FEC 2 MS    -7

DVB-S QPSK 1/2 FEC 333 KS   -9    
DVB-S QPSK 7/8 FEC 333 KS   -6    

I drew the following conclusions (but note my caveat about experimental errors!):

1. At 1/2 FEC 2 MS, DVB-S2 needs 3 dB less power than DVB-S
2. For DVB-S 333KS or 2 MS: going from 1/2 to 7/8 needs 2-3 dB more power
3. For DVB-S2 2 MS: going from 1/2 to 9/8 needs 4 dB more power
4. For DVB-S2 2 MS: going from 1/2 to 1/4 needs 4 dB less power
5. DVB-S2 Pilot symbols made no reproduceable difference at 2 MS

My draft recommendations based on this one set of tests:

1. Use 2 MS DVB-S2 H264 QPSK 1/2 FEC as the default DATV mode where possible
2. Use 2 MS DVB-S2 H264 QPSK 1/4 FEC if RX available
3. Use 333KS DVB-S H264 QPSK 1/2 FEC as default RB-TV mode
4. Test 333KS DVB-S2 H264 QPSK 7/8 FEC next time
5. Conduct further tests with pilot symbols

More to follow

Dave
G8GKQ

[G4EWJ]

Interesting. Are you able to try 8PSK?

Brian

[F6DZP]

Hello Dave,

Very interesting results, but I do not completely agree:

As, using DVB-S with narrow band we have only few place for the video, I think that we cannot compare these setups:

DVB-S QPSK FEC 1/2 SR333
and
DVB-S QPSK FEC 7/8 SR 333

as with FEC 1/2 you loose half of space for the video,
(If we continue in your way we should say that with a FEC of 9/10 ( if it should exist) we have also a better result, but no more place for the video....)

I will compare instead:
DVB-S QPSK SR333 FEC 1/2
and
DVB-S QPSK SR190 FEC 7/8
In this case, for both transmissions, you have about the same space for Video/Audio

So for DX, I will try these 2 setups that will transport the same TS, and do the comparison.

So IMHO, the question is more to choose between SR333 FEC1/2 and SR190 fec7/8 that are similar in their ES content.

About DVB-S2 at SR333 down to SR125, I think also that we cannot have an answer today, as you have not yet tested these setups.

Comparing DVB-S and DVB-S2, my first tests give something similar to you, using SR 2MS, but my results are different at SR250 or SR125: Comparing to DVB-S, I have not the same gain using DVB-S2 instead of DVB-S. (I could say not gain at all)
But I have not done the DVB-S2 tests on the air, only at home, using a low level modulator (DektecDTA107-S2) and attenuators and a MiniTiouner with a Sharp NIM.
And the Minitioune software is well optimized for low SR - DVB-S mode, but DVB-S2 version is just born, so I have not spent so much time for optimization.

To be continued....
Sure, I can have different result in 1 or 2 months, and all that I say today can be false...today... or tomorrow.

So we continue our tests.

But very interesting to do. Thank you for sharing your results.

73
Jean-Pierre