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Author Topic: Long wire antenna tuning  (Read 4133 times)
W7PV
Member

Posts: 12




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« on: March 24, 2011, 07:02:44 PM »

I just put up a 480 foot long wire, about 100 feet in the air, and was surprised my LDG tuner could not tune it on 160M.  I'm using a 4:1 balun, and have a good ground.  Any thoughts?

Paul
W7PV
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KF6ABU
Member

Posts: 351




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« Reply #1 on: March 24, 2011, 07:21:14 PM »

Well the tuner obviously has a limitation, as all tuners do. What is the SWR measurements at the antenna after the balun?
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K0ZN
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Posts: 1563




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« Reply #2 on: March 24, 2011, 07:43:26 PM »

A couple of comments:

First, why and/or how do you have a balun in that system??  Are you feeding it in the center??  If that is an end fed long wire antenna,
there is absolutely no point in a balun; it would probably be a liability. A balun is designed to match unbalanced coax to a BALANCED antenna system....and an end fed
antenna is a totally UNbalanced. This may be part of your problem.

It is almost impossible to make any factual comments without knowing more details on how your antenna is fed, grounded/counterpoises, etc.

480 ft. on 160 M is very close to a full wave length on 160. That length would present a very high impedance and a lot of reactance at the feed point,
possibly more than the tuner can handle on 160. Pick a length that presents a more friendly  Z  at the feed point.

Keep in mind that that antenna will likely be quite directional on the higher HF bands. It will have some modest gain in the main lobes,
but the lobes and nulls will be deep and significant.

Please give us more info.....

73,  K0ZN

« Last Edit: March 24, 2011, 07:50:33 PM by K0ZN » Logged
WB6BYU
Member

Posts: 13580




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« Reply #3 on: March 25, 2011, 08:39:45 AM »

Why do you have a balun?  How is it connected?  How is the antenna fed?

How do you have a "good ground" 100' in the air?  Not that this is impossible - for
example, I've used a metal window frame as a ground, and all the ones in the
building were bonded together, making a pretty good "ground" for a horizontal
end-fed wire running out the window.  But that would be a very different case
to match than, for example, a 480' horizontal wire with a 100' vertical wire
on one end dropping down to a feedpoint at ground level, or a 480' center-fed
wire.

So we really need more details on how you are feeding you wire, as it has a huge
impact on the impedance that the tuner is trying to match and what can be done
about it.
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KG6BRG
Member

Posts: 119




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« Reply #4 on: March 27, 2011, 06:02:37 AM »

I use a LDG tuner to load random wires and they will do a pretty good job, as someone else said make sure you don't have a multiple of a half wave at the frequency you want to use.  Lengthen or shorten your wire, and you need a counterpoise as well as a electrical safety ground.  A copper rod in the ground is not enough for an effective RF ground usually.  Run some radials from the tuners ground lug.  Also LDG will help with your set up if you call or e-mail.  cheers.
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W5GNB
Member

Posts: 419




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« Reply #5 on: March 27, 2011, 07:14:25 AM »

Get RID of the Balun..........
If you still can't tune the antenna, adjust the length of the wire a bit to allow the tuner to find an impedance match it likes............

73's
Gary - W5GNB
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K7ZRZ
Member

Posts: 279




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« Reply #6 on: March 28, 2011, 07:23:10 AM »

Paul,

You posted the question several days ago, but have not come back to tell us the rest of the story.  Why?  Perhaps you asked the same somewhere else and have gotten some useful advice and replies, but the curiosity remains here.  (oh don't get me started)
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Brian K7ZRZ
NA7U
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Posts: 72


WWW

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« Reply #7 on: March 30, 2011, 08:46:40 AM »

Paul,

Have you tried using a counterpoise wire? It doesn't necessarily have to be a specific length, and not necessarily long. Try different lengths and see if it helps the tuner.

Also, I found this site helpful when I was using an end-fed antenna:
http://www.aa5tb.com/efha.html
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