[mythtv-users] LNB configuration for second DVB-S2
Simon Hobson
linux at thehobsons.co.uk
Fri Aug 12 10:20:58 UTC 2011
Josu Lazkano wrote:
>Hello forum, I just bought an other DVB-S2 device and I have problem
>with LNB frecuency.
>
>I have a dish pointed to Astra19.2E and with one DVB-S2 device I have
>no problem, I just configure it as Universal LNB and it works great.
>But for the second device, I add this on the cable:
>
>http://www.ikusi.es/documentos/archivos/modelos/UDU%20EN.pdf
>http://www.ikusi.es/documentos/fotos/modelos/1717.jpg
>
>I connect the two outputs to both devices and now I have no signal on
>both devices. I must configure the LNB with other frecuencies?
You have a big problem doing that.
The LNB actually does part of the tuning - it selects one of four
combinations of polarisation (horizontal or vertical) and band (low
or high). Thus at any time you will only ever get about 1/4 of the
available channels down the cable. The tuner sends signals up the
cable that both power the LNB, and instruct it which of the four sets
of signals to select.
This is VERY different to terrestrial or cable systems where the
entire set of channels comes down the wire at the same time - and you
just pick out the one you want.
It is possible to split the signal - provided you have enough of it
to start with - but you will have to do two things :
1) You will need to disable or block the signals from one of the
tuners - otherwise you could have one sending a control signal for
one group, and the other sending a different signal. Even if they
select the same group of channels to be sent down the wire, the
signals can interfere such that the LNB doesn't get anything it
understands.
2) You will need to configure the system so that it knows that it can
only tune channels on tuner 2 that are in the group selected on tuner
1. I don't know if Myth can handle this, and if it does, how to
configure it.
The other problem you may have is that a passive splitter loses a lot
of signal - each output gets less than half the power fed into the
splitter. Unless you have an excess of signal, you may not have
enough left for the tuners to work (reliably, or possibly at all).
So in summary, no matter how difficult, you really want to get a twin
output from the LNB. I'm guessing you have an old Sky minidish - you
may find the following links useful :
http://www.satcure.co.uk/tech/page10.htm
http://www.satcure.co.uk/accs/quad_sky_lnb.htm
This guy has a LOT of information on his site.
Or just stump up and get a whole new dish fitted.
--
Simon Hobson
Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.
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