[mythtv-users] Coax splitters - how painful are they?

Todd mythtv at vbref.org
Sat Sep 29 04:30:53 UTC 2007


"R. G. Newbury" <newbury at mandamus.org> writes:
> Well I DO NOT FEAR a visit from the FAA....it would be the DoT up here 
> in the 'frozen north' (that describes our bureaucracies not our weather!)
> 
> Seriously, I want to combine a cable feed and an antenna through 
> combiner, and feed one coax to the TV. Either feed alone is fine and I 
> can switch them, but through a (cheap) combiner I get nothing
> watchable.

Hi RG, 

This occurs because it's quite a complex engineering issue.

You're trying to frequency division multiplex two broadband RF
signals.  Nothing cheap is going to do it.  To do it right, you need
to at least downconvert the OTA channels (which I believe would
require one tuner per channel) and then modulate them up into a
frequency slot that's unused on the cable feed.  The math and the
physics are not pretty.  It actually might be worse than that-- you
may need one radio (tuner) per station to pull this combining off
properly.   

> Both signals have already been split: the cable coax to feed the 
> mythbox, and the antenna has already been boosted (by a medium-cheap) 
> amp, and split three ways, 2 of which feed the HDHR unit,
> 
> This may not be the best setup.. I do not know. I do suspect that I need 
> better splitters than the el-cheapo's I had in the bottom of a box of junk.

I'd recommend dedicating a capture card to OTA, and a separate one to
CATV.  Then, if you want to also feed the TV with these signals for
watching them live, the right tool is a low tech co-ax switch.  Radio
Shack (or equiv) sells remote controlled ones.  Or if you have a an
a/v receiver or TV with multiple co-ax inputs that can be used as a
more elegant switch.  But combining broadband RF requires multiplexers
that cost thousands, best I can tell (they're used in large facility
closed circuit tv surveillance).  







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