[mythtv-users] Unicable problems

Piotr Oniszczuk piotr.oniszczuk at gmail.com
Fri Jun 10 09:40:41 UTC 2022

> Wiadomość napisana przez Klaas de Waal <klaas.de.waal at gmail.com> w dniu 05.06.2022, o godz. 23:31:
> I think I found what is wrong.
> Considering that:
> - Piotr states that a Unicable LNB needs a stable 18V supply
> - Matthias' problems disappeared after using the Power Injector that gives a 18V supply
> the problem is that MythTV still changes  the LNB voltage from 13V to 18V and vice versa according to the log messages that come when "-v channel" is given.

In my BE i have patch for this issue (see attached).
IIRC i was trying to upstream it - but as in many other cases with mythtv devs - I failed.

> This is of course needed for legacy LNB inputs but it is wrong when all tuning information is passed via the DisEqC command and the DC supply is just the DC supply.
> Also considering that a Unicable splitter has DC pass-through which means that it is NOT a good idea if one tuner gives 13V and another tuner gives 18V DC when the outputs are DC connected.

Good SCR aware spliter has diodes to avoid "feeding" power from currently 18V supplying F-connector to 13V currently supplying F-connector  

> To test this, I have made a quick hack setting the DC always to 18V and it looks like my DVBSky S950-C now works OK with the Unicable LNB.

this is qll news!

> The proper solution is of course that for Unicable LNBs the DC must always be 18V and that only for legacy LNBs the DC voltage switching (and the 22kHz signalling) must be done.
> I still need to figure out how to fix this in an optimal way but this definitely looks the way forward. By the way, it is amazing that this always has been wrong and even more amazing that it works OK with a DVBSky S952 card.

pls look at attached patch. 
IIRC it should address issue ...

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