I ended up changing the director to a reflector and the antenna
resonatews fine now. I am not sure why a de-dir would not work.
Doug N4IJ
On 6/3/10, john@kk9a.com <john@kk9a.com> wrote:
> 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@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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