[mythtv-users] HELP! In antenna hell!

Richard Shaw hobbes1069 at gmail.com
Wed Sep 29 18:14:27 UTC 2010


Ok, brief history:

My original setup (prior to DTV transition completion)  was a
HDHomerun w/ both tuners (ATSC) connected to a single DB2 UHF
antenna[1]. Everything was fine as even the VHF broadcasters where
using UHF channels for their digital TV broadcasts. I would have
occasional hickups in the signals, some more than others, but
all-in-all everything was fine.

Once analog TV was dead, two of the networks moved down to their
original analog frequency: 5 & 13. I was able to get 13 OK with my UHF
antenna but I could no longer get channel 5.

Fast forward to last week when I finally bought a CS-600 VHF
antenna[2] and Channel Master UHF/VHF UVSJ. I put both antennas on my
5' mast as far as I could apart in the attic as I really don't want to
mess with an external mast and I think it would violate my
neighborhood covenant. Now I barely get 5 even though on the HDHR I'm
getting 100% signal strength but only 50-60% signal quality and the
symbol quality drops frequently and channel 51 is all over the place
when it was solid before.

I tried moving things around in the attic while taking my netbook up
with me check signal strength (via hdhomerun_config_gui). I'm getting
80%+ signal strength in every case and in most cases 100%. I
intentionally over sized my antennas to make up for the fact they were
in the attic. It seems that the signal was much better while I was up
in the attic with the antennas.

I wonder if I could just hire someone to stand up there 24/7? :)

Now the VHF antenna is laying on the attic floor and the UHF is up as
high as I can get it. I tried moving both the antennas all around
including upside-down, facing down, facing away from the broadcast
towers, everything while watching the signal strength/quality and
nothing had a noticeable effect except getting the UHF antenna close
vertically to the VHF antenna and it only seemed to affect the VHF
antenna. Horizontal separation did not appear to help.

Googling quite a bit I've read I need a minimum of 3 feet separating
the antennas but another site said 5 and then another said twice the
wavelength (or was it 2 times the quarter wavelength?) i.e. twice the
longest element in the antenna which would be 2 x 80" which I'm not
even sure I could accomplish in my attic.

This makes my wonder. If I need so much separation, how do combined
UHF/VHF antennas work?

Here's what I'm thinking of doing next:
- Adjusting the antenna locations then coming back down from the attic
to get measurements of signal quality without me interfering with (or
improving as the case may be) the reception.
- Upgrading to RG6 quad shielded cables or maybe even RG11 but I don't
think that will magically solve my problem. Currently I've got 25'
RG59 to the UVSJ and RG6 going from the UVSJ to each antenna.

Any useful/practical advice would be greatly appreciated.

Richard

[1] http://www.antennasdirect.com/store/DB2_antenna.html
[2] http://www.antennacraft.net/CS.html


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