[mythtv-users] Big Myth system (2-3 satellite receivers + capture devices, 5 tvs, Samsung DLNA) ?

[Simon Hobson]

Linuxguy123 wrote:

>Aside: my home is wired funny.   Most rooms have a single coax from the
>utility room to the TV locations, supposedly for cable.   Almost all the
>TV locations also have a Cat5 feed from the utility room.  
>
>My satellite system requires 2 coax feeds from the LNB to the receiver
>in order to view HD content.  I'd have to rewire the entire house to get
>2 coax feeds to everyplace we want a TV.

Not true - you need two LNB feeds to allow two tuners (ie get the 
"watch one, record another" facility). The HD signal comes down 
exactly the same cable as an SD signal.

Some devices can be told not to use both tuners (for situations like 
you describe) which will allow all the functionality - but restricted 
to what can be done with one tuner instead of two. Eg, you can still 
record something while watching something else, you can still pause 
live TV, etc - but you can't watch one thing live while recording 
something else, and you can't record two things at once.
Technically, there is a halfway house supported by some - by 
splitting the LNB feed you can still have two tuners BUT the second 
can only access the same band and polarisation as the first (roughly 
a quarter of what's available).

The reason for this is, unlike terrestrial where the whole spectrum 
of usable signals comes down the cable together, on satellite some of 
the tuning is done in the LNB. The LNB (Low noise Block Converter) 
shifts the received signal from something very high in frequency 
(well up into microwave territory) down to something that will travel 
reasonably well in a coax cable. It can select one of two bands (low 
and high), and also select by polarisation (horizontal and vertical). 
Thus only about 1/4 of the possible signals are ever present on the 
coax at any time, and so you can't split it without significant 
compromises.

-- 
Simon Hobson

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