Antenna wiring question

Discussion in 'Archived Threads 2001-2004' started by Scott Kriefall, Jul 6, 2002.

  1. Scott Kriefall

    Scott Kriefall Second Unit

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    I recently replaced the old, semi-dilapidated VHF-only antenna on my roof with a new VU-75XR from Radio Shack. Only the antenna itself was replaced -- all wiring, mounts, etc, were reused.

    I'm about 5 miles from the broadcast antennas. Although the VHF performance of the antenna is great, the UHF performance -- which is what I'm really interested in -- is poor.

    I've compared the performance of this antenna to that obtained from the well-known Radio Shack Double Bowtie antenna placed on top of my Mitsubishi TV. Up through channel 29 or so, the rooftop antenna appears to outperform the bowtie. It's a draw on channel 32. Channels 35 and above, the bowtie dramatically outperforms the rooftop antenna. The antenna is on a rotor and I've tried reaiming it many times, without much improvement.

    I'm wondering if this disappointing performance might be due to the odd manner in which a previous owner wired the antenna:

    Standard 300->75 ohm transformer at the antenna, with coax leading down to the entry point on the side of the house. At that point, the coax enters a weatherproof plastic box and is connected to a 75->300 ohm transformer. To this transformer is connected old-style 300-ohm twinlead which is brought into the house; there's probably about 20 or 30 feet of the twinlead that terminates in the utility room. The twinlead is then connected to another 300->75 ohm transformer, which is then connected to a common 2-way 75-ohm splitter.

    I've connected one of the outputs from that splitter into a satellite diplexer, along with the output from my DirecTV dish. There is, of course, another diplexer at the other end of that line, and the VHF/UHF output from there is what I have connected to my HDTV tuner.

    Would replacing the twinlead with RG-6 coax be likely to solve some of these problems? If so, what would need to be done to ground the antenna? Whoever installed the existing wiring grounded the twinlead to a water pipe inside the house, and that would obviously need to be replaced if I no longer use the twinlead.

    Could I install a diplexer on the roof and then connect the antenna directly into one of the outputs from the dish's multiswitch? That would be much easier for me, as I doubt whether I'd be able to handle the installation of a new lead-in coax run -- and I'm unsure whether any installers would be interested in such a minor job.

    Thanks for any suggestions!
     
  2. Wayne A. Pflughaupt

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    Hi Scott,

    I know just enough about antennas to “keep from blowing myself up,” as it were, but I think I can handle most of what you’re asking.

     
  3. Scott Kriefall

    Scott Kriefall Second Unit

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    Thanks for the response.

    I've done a small bit of reading myself. It appears that the antenna mast itself should be grounded, and so should the wiring (coax or twinlead) where it enters the house. I'm going to have to crawl up on the roof again to verify, but I don't believe the existing mast is connected to any sort of ground -- unless it's somehow grounded through the rotor device in which it's installed.

    I'm beginning to think that I should just call an installer, and have it professionally fixed. But I'll wait to see if anyone has any comments regarding usage of the diplexer/multiswitch. The antenna must have been like this for 20 years; a few more days or weeks probably won't hurt...
     

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