[mythtv-users] HELP! In antenna hell!

Craig Treleaven ctreleaven at cogeco.ca
Wed Sep 29 18:50:18 UTC 2010

At 1:14 PM -0500 9/29/10, Richard Shaw wrote:
>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.
>[1] http://www.antennasdirect.com/store/DB2_antenna.html
>[2] http://www.antennacraft.net/CS.html

Combining antennas is a black art--weird interactions between them seem to plague some people and bypass others.  You seem to be in the former camp.  Two options:

1) Don't combine them--dedicate one tuner to your VHF channel(s) and the other to UHF.  Run an extra coax and play with the placement of each antenna individually.

2) Can you return the CS-600 and get a combo UHF-VHF antenna?  Something like the Channel Master 4242?
The downside is these are whopping big antennas.  I don't know if they are delivered unassembled so that you can get it into your attic.

If you want to persist with combining, I'd suggest the digitalhomecanada site.  They have a good faq written by some experienced RF people that may help.


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