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DVB-S questions
Posted: Wed Jan 06, 2021 4:35 am
by N7CS
A few questions for the group...
Q1:
I saw a note a month or so ago that mentioned there was a new standard for UK DATV repeaters that would use only 1.2 MHz of bandwidth. I can't seem to find the old note anymore, but I was wanting to know what are the full set of DVB-S (or is it -S2?) parameters to enable it to work at that bandwidth.
I'm currently experimenting with DVB-T in the US at 2 MHz bandwidth, but am looking to find something that requires less bandwidth.
Q2:
When forum posters are talking about DVB-S, I often find references to mega-symbols per second. What's the formula to convert that into bandwidth in MHz?
Q3:
I recall seeing another article talking about some ultra-low bandwidth DVB-S2 experiments done by Dutch amateurs recently on 2m, but I wasn't sure what they got the bandwidth down to. It might have been 0.2 MHz, but I wasn't sure. I wasn't able to find a lot about this in English. If anyone has details on the parameters and bandwidth used for those experiments, that would be helpful too.
73,
Burt Guillot N7CS
Re: DVB-S questions
Posted: Wed Jan 06, 2021 10:43 am
by radiogareth
Some interesting questions Burt. I can't answer any of them but there is a lot of very narrow band stuff (in amazing quality too) being sent on QO-100. How its generated and how its decoded would be a couple of extra questions that would expand on the general knowledge base. There is also a BATC team working on developing NB DVB-T hardware and software at the moment, there is a lot going on.....
Gareth G4XAT
Re: DVB-S questions
Posted: Wed Jan 06, 2021 10:45 am
by g8gtz
Hi Bert
Q1 - The original article was in CQ-TV 266 and BATC are recommending 1Ms DVB-S2 2/3 FEC with H264 encoding but some groups are now using 500ks DVB-S2 2/3 and H265 encoding and get very good results.
Q1a - BATC have just started a project using a tuner / NIM which enables narrowband DVB-T OFDM down to 200KHz wide - for more details see
https://wiki.batc.org.uk/Knucker
Q2 - try this on-line calculator
http://www.satbroadcasts.com/DVB-S_Bitr ... lator.html
Q3- We typically use 150 KHz - 500KHz on 146 MHz but there have been some very successful tests using 35 ks (50KHz) DVB-S2 full frame rate H265 on the Oscar 100 satellite with amazing results.
Hope this helps.
Noel - G8GTZ
Re: DVB-S questions
Posted: Wed Jan 06, 2021 12:27 pm
by g0mjw
N7CS wrote: ↑Wed Jan 06, 2021 4:35 am
A few questions for the group...
Q1:
I saw a note a month or so ago that mentioned there was a new standard for UK DATV repeaters that would use only 1.2 MHz of bandwidth. I can't seem to find the old note anymore, but I was wanting to know what are the full set of DVB-S (or is it -S2?) parameters to enable it to work at that bandwidth.
I'm currently experimenting with DVB-T in the US at 2 MHz bandwidth, but am looking to find something that requires less bandwidth.
Q2:
When forum posters are talking about DVB-S, I often find references to mega-symbols per second. What's the formula to convert that into bandwidth in MHz?
Q3:
I recall seeing another article talking about some ultra-low bandwidth DVB-S2 experiments done by Dutch amateurs recently on 2m, but I wasn't sure what they got the bandwidth down to. It might have been 0.2 MHz, but I wasn't sure. I wasn't able to find a lot about this in English. If anyone has details on the parameters and bandwidth used for those experiments, that would be helpful too.
73,
Burt Guillot N7CS
The bandwidth if a function of the symbol rate and filtering used - EN302307. The DVB-S2 standard has three roll-off factors 0.20, 0.25, and 0.35. So, a typical 333ks signal occupies 450kHz with 0.35 roll off and 400kHz with 0.2 roll-off. DVB-S2X also has 0.15 and 0.1 roll-off. There is a calculator here:
http://www.satbroadcasts.com/DVB-S_Bitr ... lator.html
We have been experimenting with 35 ks/s which fits nicely in a 50 kHz channel and latterly with 25ks/s which fits into 30 kHz. The video quality at 35ks still leaves a bit to be desired but in 333ks it's possible to send HD video, so there is no need for 2 MHz wide signals any more. Very good quality is possible with 125ks/s and even 66ks/s.
On the DVB-T side. Recent experiments have worked down to 250kHz bandwidth but it's currently a lot better at 500kHz with performance for QPSK much the same as 333ks DVB-S.
Mike