[TowerTalk] EFHW

john at kk9a.com john at kk9a.com
Sat Jul 15 13:19:26 EDT 2017

I have no experience with end fed wires but I imagine that the counterpoise
has an effect on the resonant frequency.


To:	towertalk at contesting.com
Subject:	[TowerTalk] EFHW
From:	Tom Osborne <w7why1 at gmail.com>
Date:	Sat, 15 Jul 2017 09:20:58 -0700

Hi All

I built 3 UNUN's for some EFHW antennas I plan to use.  On 2 of them, I
used 1 FT-240 mix 43 core (will be running these as portable antennas on
LP) and one one of them I used 2 of the same cores.

With around 135 feet of wire, the 80 meter SWR is right where I want it -
around 3550.  But - when I go to 40, the SWR is lowest around 6950.  If I
increase the length of the wire to bring the frequency up on 40, it will
resonate around 3700, on 80 which is not what I want.

The UNUN's I build have 2 turns of twisted wire wrapped around the core,
and then 5 more to make 7 turns.  Then it crosses over to the other side
and has 7 more turns.  This seems to be what most of the ones I found on
the 'net have, Across the coax connector I have 150pF capacitance.

Why would the 2nd harmonic be so far off on 40?  Is there a better turns
ration solution for the cores??  Tanks and 73

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