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 Post subject: long wire antenna and metal roof question ?
PostPosted: Nov Tue 14, 2017 1:04 am 
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Joined: Jan Mon 02, 2017 4:06 pm
Posts: 20
Hi guys I have a long wire antenna made of no.12 insulated stranded THHN electrical wire about 75 feet long connected to a pole about 25 feet above the ground. I have a plastic insulator between the pole and antenna wire. The other end is connected to a plumbing vent pipe on my roof which is metal. The antenna wire is connected to a plastic insulator about where the metal roof line begins. In other words the antenna wire doesn't go over the metal roof; however the lead in wire does come within 1 foot of the metal rood and then though a metal window frame. My question is should I use shielded coax cable for the lead in because it comes close to the metal roof and through a metal window frame ? Thanks in advance for your help.


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 Post subject: Re: long wire antenna and metal roof question ?
PostPosted: Nov Tue 14, 2017 1:12 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 11533
Location: S. Dartmouth MA 02748-1225 USA
No, The antenna as described is a Marconi inverted "L". the downlead is part of the antenna is very high impedance at most every received frequency. It will not match coax and the shield will actually bypass the signal from the center conductor to the shield because of the miss-match and the effect of capacity between the center conductor and the shield. Move the insulator away from the soil pipe end so the downlead can be at an angle at 90 deg or greater, pointing to the home. Do use a ground rod and lightning arrestor at the entrance of the downlead into the home.

YMMV


Last edited by Chas on Nov Tue 14, 2017 3:05 am, edited 1 time in total.

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 Post subject: Re: long wire antenna and metal roof question ?
PostPosted: Nov Tue 14, 2017 1:30 am 
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Joined: Aug Thu 20, 2015 3:09 pm
Posts: 541
Location: Albion, CA, USA
I'm assuming that the end with the vent pipe also has an insulator. Otherwise I see no problem with your set up. The thing to avoid with wire antennas is running parallel and close to metal such as the roof. Keep as much separation from the widow sill as you can, but don't worry too much about it. How well does the antenna seem to work?


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 Post subject: Re: long wire antenna and metal roof question ?
PostPosted: Nov Sat 18, 2017 8:41 pm 
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Joined: Jan Mon 02, 2017 4:06 pm
Posts: 20
Thanks for the advice guys. This antenna does not seem to work as well as the previous one. My old antenna was a radio shack long wire antenna kit with bare wire.


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 Post subject: Re: long wire antenna and metal roof question ?
PostPosted: Nov Sun 19, 2017 8:44 am 
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Joined: Jul Fri 18, 2008 10:02 am
Posts: 2006
Location: near ST Louis Mo 62002
I have installed numerous inverted L antennas on Tow boats on the inland rivers , as long as your wire 10 to 15 feet above the metal roof it will act as a ground plane and make a marvelous antenna .

This was back when all the boats used SSB radios to communicate with the office , now days cell phone and satellite has taken their place .

https://images.search.yahoo.com/search/ ... =11t3nfcl1

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Mark
(Conti the brain damaged robot )


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