Is there a choke between the ground plane and the center conductor?
An ohm meter will confirm.
Hygain was famous for that.
73, Jim w7ry
On Mon, Aug 8, 2022, 12:26 AM Jim Pruitt <jpruitt67@gmail.com> wrote:
> About 4 years ago I picked up 2 bottom sections of what I think were 11
> meter ground planes. The section looks like the bottom section for a
> HyGain 18AVQ vertical or similar. The only difference is the mounting
> flange has a plate that holds what looks like about ½" diameter ground
> radials. The issue I am having is that I used that mounting section to
> make a 20 meter vertical. Easy enough, right? WRONG. I used mating
> tubes to make the ¼ wave 20 meter vertical but it resonated at...ready
> for this.... 39mhz! Then I grabbed the second one and used it. Now it
> resonates at 13.5mhz but shortening the vertical does not bring the
> frequency up. I am wondering if perhaps someone (CBer maybe) ran way
> too much power through them and broke down the dialectic of the plastic
> (or whatever that is) insulator that isolates the vertical from the
> mounting bracket and ground. That is the only explanation I can come up
> with as to why it is so far off.
>
> Does anyone have any suggestions as to how to fix the problem?
>
> Thank you.
>
> Jim Pruitt
> WA7DUY
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