[mythtv-users] Signal strength issues changing from NTSC to QAM256

Alan Marchiori alan at alanmarian.com
Mon Jul 6 19:30:42 UTC 2009


On Mon, Jul 6, 2009 at 12:59 PM, Tony
Sarathchandra<tsarathchandra at yahoo.com> wrote:
>
> So at the start of this month, the much discussed analog to digital cutover
> of Comcast channels >32 occurred in my area (Bay Area). Prior to this change
> I had been happily receiving channels 2-89 or so via the NTSC input of my
> HVR-1600 MythTV BE/FE setup.  I had been using the ATSC input of the
> HVR-1600 for OTA DTV as well which was working well.
>
> So I temporarily disconnected the OTA ATSC input, hooked up the Comcast
> cable to this input, changed config to QAM256 in mythtv-setup and did a
> scan, nothing!  After fiddling a bit the details of which I will spare here,
> I found that I was able to pick up most of the QAM channels, albeit some
> quite poorly, if I bypassed the 3-way splitter which I was using to split
> the Comcast signal between the HVR-1600 and my older AVerMedia TVPhone98
> (bttv compatible) card being used as a second tuner near my MythTV BE
> server. Here's a primitive diagram of how the coax cabling is laid out at my
> place.
>
>
>                 |----3.5dB-------->HVR-1600 NTSC input (MythTV Backend)
>
>   Comcast cable in--->[SV-2G 2-way splitter]---3.5dB------>[SV-3G 3-way
> splitter]|----7.0dB-------->HVR-1600 ATSC/QAM input (MythTV Backend)
>
>
> |
> |----7.0dB-------->AverMedia NTSC input (MythTV Backend)
>
>                                 |------------3.5dB------->TV
>
> I have an initial 2-way splitter as you can see going to a TV in another
> room. I'm guessing that the signal level after this initial 3.5dB loss and
> the subsequent 7.0dB loss is not sufficient enough to the QAM tuner to
> detect a strong enough signal.  Any thoughts on how I can alleviate this
> situation as I do need the splitters in place to use all the tuners in the
> house?
>
> Should I invest in a cable amplifier at the initial 2-way splitter point?
> Would this improve the QAM signal strength sufficiently? I've also been
> looking adding a second ATSC/QAM tuner to my setup as I do want to receive
> OTA DTV as well, would something like a HD Homerun be more able to operate
> with lower signal levels that the HVR-1600? Any feedback much appreciated.
>


Seems plausible to me.  I had problems with our comcast cable modem
disconnecting they came and installed a amplifier that looks a lot
like this one http://www.solidsignal.com/prod_display.asp?prod=CM3410
but a generic brand.  After that no problems.  I wasn't using myth QAM
at that point so I don't know about QAM in particular but now I do use
QAM from comcast (through the amp) with no problems.  In our setup it
is installed off the main line from the street coming into the house
and then it goes through 2 splitters before hitting the HDHR and only
1 before the cable modem.


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