[mythtv-users] Unicable problems

Klaas de Waal klaas.de.waal at gmail.com
Sun Jun 5 21:31:28 UTC 2022

On Sun, 5 Jun 2022 at 11:18, Piotr Oniszczuk <piotr.oniszczuk at gmail.com>

> > Wiadomość napisana przez Klaas de Waal <klaas.de.waal at gmail.com> w dniu
> 03.06.2022, o godz. 23:00:
> >
> >
> > I have my setup with a "DUR-line UK 124-3L dCSS - Unicable LNB" working
> correctly! I can now make a perfect channel scan with mythtv-setup.
> > The difference is that I replaced the single tuner DVBSky S950-C card
> with a dual tuner DVBSky S952 V3.
> > At this moment I only use one tuner of the two available; when the new
> splitter arrives (special for Unicable, DC coupled and 5-2400MHz) I will
> test with both tuners.
> > For now it looks that the card does make the difference.
> >
> > I have now documented the procedure in the Channel Scanning WIki pages,
> similar to the description of Piotr, but with more words.
> > With this procedure my DVBSky S952 cards do work OK with Unicable.
> >
> > After that I went back to the DVBSky S950-C card, configured with the
> same procedure.
> > This card still does not work reliably, with behavior similar to what
> Matthias describes.
> Klaas,
> It clearly looks to me like issue is with S950-C card as another card
> works ok with your SCR LNB.
> So i have 2 hypothesis:
> (1) 18V power supplied from card to LNB.
> (2) Diseqc issue on S950-C (whatever sw. or hw)
> Ad1: SCR requires constant, stable 18V supplied to LNB. Can you look with
> multimeter what card provides to LNB?
> (ideally will be to look with oscilloscope to see there is no ripples,
> noise and voltage is constant - even when card send diseqc commands to LNB
> and LNB controller executes commands to tune user-band PLL to req.
> frequency)
> Generally - SCR LNB requires more from SAT tuner card in terms of power
> (amount, stability). Maybe S950-C has too weak disecq power design to
> reliably power Your SCR LNB?
> Ad2: Suspecting diseqc communication (see at end of
> http://www.vdr-wiki.de/wiki/index.php/SCR_Satellite_Channel_Routing) may
> be unreliable - I added in MythTV SCR capability of multiple sends of the
> same command (enabled when repeat is set to >10).
> Did you try play with this?
> (it is required for my Inverto Unicable LNB; I have set it to 13)
> >
> > To get an indication whether this is a MythTV software problem I have
> now also used minisatip (see https://github.com/catalinii/minisatip) to
> handle the S950-C card; MythTV is configured to use the Sat>IP protocol to
> talk to the minisatip server. This configuration has similar behavior and
> similar problems. This makes it unlikely, although not impossible, that it
> is a bug in the MythTV Unicable implementation.
> > Note that when the S950-C card is connected to a normal ("legacy") LNB
> the card works OK.
> >
> > @Mathias, it would be interesting to know if your tuner cards do work OK
> when using the minisatip server to control the cards with Unicable.
> > @Piotr Oniszczuk  it would also be interesting which tuner cards you
> have tested with Unicable.
> it is 2x dual DVB-S2 DvbSky S952.
> 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
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.
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.
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.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mythtv.org/pipermail/mythtv-users/attachments/20220605/b8186c33/attachment.htm>

More information about the mythtv-users mailing list