David J Taylor GM8ARV 🏴󠁧󠁢󠁳󠁣󠁴󠁿 🇪🇺

On 03/02/2023 13:01, James Brown wrote:
I don’t think I am alone in seeing a decrease of about 0.1 since the ‘recovery’.
Looking at the graphs, rather than the numbers,my feeling was that C4 (BAS/HVS-1) ended up a little lower in SNR at the end of yesterday compared with the start. Austria. On the other hand C3 (HVS-2/Italy) was unchanged. All this is difficult to judge because of the local and Europe-wide variations during the day.

Looks like the snow has got to Poland now, and even a heated dish hasn't been enough protection.

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Ernst Lobsiger

On Thu, Feb 2, 2023 at 03:36 PM, Charlie wrote:

I thought the demodulator/FEC blocks were separate in the STV0910 between the inputs! Perhaps I was wrong here, the cut-down datasheet only has an ambigious block diagram.

First time I've seen that behaviour in any case; anyone using the TBS 6903 or 6908 on Linux witness the same?


how the stv0910 demod chip is fed depends on the setting of the tuner chip stv6120 and matrix switch in front (single cable, two cables).

We probably never had a situation with such big SNR differences between HVS-1 and HVS-2 before (and now these are even H and V).

The LDPC block is shared between the two demodulators. See apsk16 single mode and dual mode on the TBS-6903 specs tab here.

I remember Konstantin Dimitrov saying: "The only difference between single mode and dual mode is how the LDPC is accessed."
Maybe LDPC is shared 50/50 in dual mode while in single mode each demodulator gets whatever it takes? I faintly remember
(this might be all wrong) that even under single mode I could still tune two transponders. This might lead to a situation where
HVS-2 with low LM disturbs HVS-1 similar to HVS-1 disturbs BAS (that's now 100% speculation though ;-).

The TBS stv091x driver module has a switch for single mode. I have no PC setup with a TBS-6903 now but maybe you can
check in the code how your DD driver handles this single/dual stuff and what it means for peeking and poking registers...

My two cents,


I get a slightly different front end (STV6111 per F connector and no matrix) on my setup compared to the TBS cards. Half wonder if that's what kept mine running better in the previous handover issues (the pilot is now set on for BAS, I'm convinced that was 3/4 of the problem...) but really guessing at this point. Single mode is a module option in ddbridge so it is there.

The shared FEC/LDPC would 100% explain what I saw with those particular signal conditions though, and possibly why it only affected HVS-1 and not BAS!