[mythtv-users] HD and cable

Brian Wood beww at beww.org
Mon Dec 31 00:33:56 UTC 2007


A JM wrote:
> So, the problem is more frequency related???
> 
> If you were going to try and combine the "over the air" locals and cable
> what would you use? a simple splitter in reverse or do they make
> something different for combining signals I've seen one for satellite
> and antenna's a diplexer...?
> 
> When you say the "frequencies might be the same" would that be only the
> local channel frequencies or possibly a different channel on cable might
> match up with the over the air frequency of a local channel? If it's
> locals then that would be ideal...

TV OTA broadcast signals are either VHF (54 - 216 Mhz.) or UHF (470 -
890 Mhz.)

Most Digital OTA signals (ATSC) are in the UHF range, but some are VHF.

Cable systems use frequencies from 5 Mhz. to 1Ghz. (and maybe higher
these days).

If, in your particular situation, no OTA channels conflicted with any
used by your cable company (an unlikely situation), you could
theoretically use a hybrid combiner or a directional coupler to combine
your antenna and cable into the single TV input.

I would not advise this, for a lot of reasons, including the possibility
of your antenna radiating signals into the atmosphere that are not
intended to be there and beats being created in your RF frontend by the
combination of various signals.

You could just use an A/B switch, these usually have enough isolation to
be "safe".

You might well still have to reset and perhaps rescan the channels of
your TV set.


> 
> Given that the tv only has a single coax input what was the manufacturer
> thinking and why include "over the air" as an option, it seems kind of
> stupid...

It may have been thought of as an "either or" situation, not a "both at
the same time". My set (Hisense) has separate RF inputs for the antenna
and cable, though the latter is only an NTSC tuner, I have to use my
Myth system to demod QAM.

> 
> My other set I have does a scan on cable and there are no HD locals that
> show up so I am guessing that would be the case on my new set as well.

I still think the cable co's are supposed to provide whatever digital is
available off-air, I'll look into it further but I've been a tad busy
lately.

beww





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