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[Towertalk] Shortening Inverted L Antennas

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Subject: [Towertalk] Shortening Inverted L Antennas
From: KevNathan@DSB.WA.GOV (Nathan, Kevin)
Date: Mon, 22 Jul 2002 09:22:42 -0700
Hi All,

Thanks again to all who gave me information about shunt feeding my tower for
160 and/or 80 meters.  I'm still thinking about this possibility but want to
look at another as well.  I am inspired in this second line of thought by
the antenna I just sent back.  It was, as I said in my post, an inverted L
for 80 and 160 with something called a resonactor in it.  It was shortened
to 105 feet by this resonactor and on air tests on 160 were pretty good with
it.  Just not good enough in light of it's problems on 80 to keep it.

However, the idea of an inverted L still sits there in my mind since I have
the radial system in place and a way to mount one.  So, here's my question.
This antenna can go up about 45 feet to the 2X4 crossbar on my tower and
then out for the remainder of its length.  The far end would end up perhaps
20 feet off the ground if I'm lucky.  To keep it on my property, I will need
to physically shorten it and then load it to achieve resonance.  A couple of
questions arise from this.  First, is there a good rule of thumb to use
regarding how much coil to use to achieve a given amount of shortening?
I've read some articles where you wind the same length of wire onto a coil
form as you want to shorten the antenna i.e. if you want to make the antenna
20 feet shorter, wind 20 feet of wire on the coil and so on?  Is this a good
place to start in practical terms?  Second, again is there a good rule of
thumb for where to place the coil?  I'm assuming in the horizontal section
but how far back from the end.

I would sure appreciate any practical advice on this and thank you in
advance for your help.  73
Kevin, K7RX

Kevin Nathan, Independent Living Coordinator
Dept. of Services for the Blind 
3411 S. Alaska
Seattle, Wa 98118
Voice:  (206) 721-6450
Cell:  (206) 604-4767
Toll Free:  (800) 552-7103
Fax:  (206) 721-6403

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