[TowerTalk] MORE - 2 element 20m yagi resonates too high in frequency

[john at kk9a.com]

Did you model the antenna and your resonate frequency is higher?   I think 
that testing the antenna by aiming it into the ground is not a reliable 
test, I would raise it up at least 35' high and then test it.

BTW, You can easily build a two element yagi (with a reflector) using 
insulated elements that has close to 50 ohms impedance and eliminate the 
match and associated adjustments.

John KK9A



To: towertalk at contesting.com
Subject: [TowerTalk] MORE - 2 element 20m yagi resonates too high in 
frequency
From: Doug Snowden
Date: Thu, 3 Jun 2010 11:15:11 -0500


I am wondering if my problem with the yagi is that I am using an old
driven element clamp that came from an old hy gain beam.  Could the
capacitance from the driven element clamp (grounded) to the driven
element be raising the resonant freq?  I don't know what the
capacitance would be, but I would think 20-30pf.  That would be across
the two halves of the driven element.



Doug N4IJ

My original post:

> >> I am curious about this: I am experimenting with a 2 element beam for
> >> 20 meters.
> >> It is driven element - director arrangement. I haveit near the ground
> >> with the director
> >> near the ground and the driven up about 10 ft off the ground, in other
> >> words forward
> >> direction is into the ground.. In looking at the resonant point, it is
> >> resonant around 14.6 mhz. The boom is about 9 ft long. I would expect
> >> it to be lower than the design freq than higher. Could it be some
> >> strange interaction witht eh ground since it is de/dir ?
> >> I know it is recommended that with e reflector you have the reflector
> >> on the ground when doing inital testing. I'll try and elevate it to
> >> see what is going on, but it seems
> >> strange to me. I am using a beta type match, so I can tune it, but the
> >> lowest
> >> swr is at 14.6.
> >>
> >> Anyone seen this sort of thing before?
> >>
> >> Doug, N4IJ
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