As a point of reference, I wound a feed point choke for a JK 20M yagi
out of THHN and found the apparent resonance had shifted well below the
band compared to the other JK 20's on site fed with otherwise identical
baluns but made from RG400 coax. The antennas are all well up in the
air (lowest is 80'. We're using it as-is so far, but the SWR on phone
is pretty bad.
I believe it's a thing.
-Steve K8LX
On 01/12/26 1:46 PM, Tom Hellem wrote:
TT'ers:
I made a choke to place at the feed point of a 20 meter vertical dipole.
9 turns of #14 thhn wound on a 2.4" mix 31 ferrite toroid.
After I installed the choke, the resonant frequency appears to have
moved approx. 1 mhz lower.
Is this the behavior I should be seeing?
I've used plenty of chokes on yagis, etc and never noticed this
before.
Modeling in Eznec shows that changing the ground constants
does not appreciably change the resonance, so it seems that the fact the
ground getting wetter between the two measurements would not
be the cause.
Any ideas?
Tom
K0SN
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