[mythtv-users] How to best deal with Comcast's "Improved" Lineup?

Brian Wood beww at beww.org
Wed Jul 21 12:55:18 UTC 2010

On Wednesday, July 21, 2010 04:17:51 am Craig Huff wrote:

> And another problem...
> In the setup directions for the DC50Xu, after directing that the DTA
> be set to channel 3 for set-up, there is a note: "Note: Some parts of
> the country use channel 4.  If you do not have a picture after
> completing the activation, you may need to switch both your TV and the
> DTA to channel 4."
> Does anyone know it that means my scheme described above of combining
> one DTA outputting on channel 3 with one on channel 4 is toast?

STBs (and their predecessors, "converters") usually output on wither channel 2 or 3, or channel 3 or 4. This is so that 
you can use a channel that is not used over-the-air in your area, to prevent interference. In the says of single-braid 
RG-59, before quad shielded cables, this was necessary. Generally adjacent channels are not used in any market, so at 
least one of the available output channels would be usable.

Now that most OTA stations have moved to UHF (there are exceptions), it's more likely that you will have both 2 and 3, or 
3 and 4, clear of any OTA signals, so you might think it would be OK to use both.

The problem is the output of STBs is extremely "dirty", the output on channel 3, for example, is very likely to throw crap 
that's within the channel 4 bandwidth. Also, the aural carrier from an STB's modulator is down by 10 db., which is normal 
for OTA broadcasts, and will throw "beats" into the upper adjacent channel. Cable companies run aural carriers at 15-17 
db. down, in order to be able to use adjacent channels without problems.

So there is a very good chance that combining the outputs of two STBs will result in crap from one interfering with the 
other, unless good filters are used in the combining network, which is expensive (and is the reason the STB outputs are not 
well-filtered, too expensive).

It might work, but I'd expect problems. You'd have to try it out I guess.

A couple of high-quality bandpass filters would probably help, but would cost more than your entire Myth setup.

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