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Re: [TowerTalk] 30m Dipole

Subject: Re: [TowerTalk] 30m Dipole
From: "Dan Zimmerman N3OX" <>
Date: Thu, 3 Aug 2006 17:30:29 -0400
List-post: <>
I think the implicit assumption throughout this thread is that you're
comparing a coax fed dipole that you trimmed to be resonant at 3850kHz
with a coax fed dipole that you just put up after cutting based on
468/f (resonant somewhere like 3200kHz or 4050kHz maybe?) and you use
a tuner to bring the SWR to 1:1 to make the radio happy.  Both of
these antennas will have essentially identical ERP if the same power
appears at their feedpoint terminals.

So if the tuner is in the shack, the difference is only due to
feedline loss and tuner loss, which, on the low HF bands are probably
also negligible or close to it.   If the SWR is very high at the
antenna and/or the feedline is not low loss, then you can lose a lot
of power in your feed system.  Using your 3200kHz dipole on 7MHz is a
much different situation than using it on 3850kHz as far as loss goes.

I think the point is that you'll not ever be able to tell a practical
difference between your 3850kHz resonant dipole 70+j0 and a dipole
that's 70+j250 on 3850kHz , so if you've got the autotuner, just hang
it and go!


> Are you making some assumptions here?  What is I have a perfectly resonant
> coax fed dipole at 3850 KHz at 140 feet and run 200 watts CW.  Now compare
> this to a 30 foot long piece of wire at 20 feet fed directly with a tuner at
> the same frequency.  Is ERP affected in this case?
> 73, Keith NM5G

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