[mythtv-users] How to limit 2xDVB-S (+DiSEqC) to 1 LNB at a time?

[David Lister]

Mike Perkins wrote:
> Simon Hobson wrote:
>> David Lister wrote:
>>
>>> Is there a way which would allow e.g. 2-4 sats for 2 tuners with one
>>> cable? :) I'm still new to this...
>>
>> No.
>>
>> The reason is that unlike terrestrial where you just feed a load of
>> signal down a cable and the tuner picks out what it wants, with sat,
>> the LNB does some of the conversion. In a basic single sat system,
>> signals sent up the cable will typically select high or low band, and
>> horizontal or vertical polarisation - thus selecting one of four sets
>> of signals. Since only one of the four sets of signals can be sent
>> down the cable at once, that puts limitations on what signals can be
>> tuned if you split the signal and run multiple tuners off it - ie the
>> separate tuners can only access signals that are in the same band and
>> on the same polarisation.
>>
> Interesting. Perhaps there's a case for a feature similar to multi-rec
> here? Where the tuner(s) can select channels from the subset which the
> LNB has chosen?
> 

That's what I was originally thinking. Both tuners would, of course,
share one polarisation/band, but that still allows many different freqs
to be tuned! It could switch to other band/pol when required and if
possible. Myth knows all the information necessary to allow for this.

For example, my providers use horizontal upper band for all the channels
except for 6 uninteresting ones. I don't even need complicated detection
and band/pol conflict resolution, all I do is switch between 19.2E &
23.5E (both upper H band). Myth should just know that both cards can
only be switched as a whole, to the same band/pol. It's not complicated
at all, actually. Try this yourself - how many favourite channels are in
one band/pol, or better, how many of the possible 4 combinations do you
actually routinely use concurrently?

Lower band: 10700 - 11800 MHz
Upper band: 11600 - 12800 MHz
(some LNB's might not overlap, so switching freq would be 11700)

This would allow something like multirec^2. No other SW can do this
AFAIK. Making myth aware would bring DVB-S closer to the simple setups
of the analogue. One cable, as many tuners as you like. Sure, there is
the band/pol limitation, but it's DAMN well better than just a single
tuner, single multiplex!

You see my point? It's just a matter of creating a new grouping
category; like input groups, but for DVB-S switching, let's say Switch
Groups. :) Cards in the same switch group would be kept on the same
band/pol. The scheduler would consider this and be able to identify and
resolve conflicts as it does with regular multiple tuners, DiSEqC
switching, multirec, etc!


Regards,
David