Tom Rauch wrote....
>
> Message: 8
> Date: Tue, 27 Sep 2005 19:25:09 -0400
> From: "Tom Rauch" <w8ji@contesting.com>
> Subject: Re: [TowerTalk] Top hat on mobile usefull?
> To: <chief@thechief.com>, <towertalk@contesting.com>
> Message-ID: <004601c5c3ba$b4624680$6401a8c0@akorn.net>
> Content-Type: text/plain; charset="iso-8859-1"
>
> > I had a homebrew bugcatcher style mobile antenna I used
> on 40m CW. I
> > placed a tophat about one coil length above the loading
> coil by using a
> > second Delrin coil center rod on top of the coil. I did
> that in order to
> > reduce the capacitive loading between the tophat and the
> coil. In your
> > opinion, do you think that distance would be enough to
> mitigate the possible
> > coil losses?
>
> I'm not sure what you are describing. Of course if you
> removed the electrical connection the hat wouldn't do much
> of anything, so I'm assuming the hat is still connected
> through a conductor to the top of the loading coil.
>
> Adding a dielectric in the path of an electric flux does not
> reduce distributed capacitance through that area, it
> increases it.
>
>
> 73 Tom
Tom,
Yes, the capacity hat was connected to the top of the coil with a wire.
The extra delrin rod was merely to put some distance between the coil and
the capacity hat in order to reduce the capacitive coupling between the two.
I figured the delrin rod and wire was the least disruptive of the coil Q,
compared to using something like a short piece of mast material.
As for the rest of your message, you cleared up an important point for
me, that the ground losses are greater than the coil loss. All of my
previous questions and proposals are no longer important. I thought I was
willing to sacrifice radiation resistance in favor of lowering the loss in
the coil. But if the ground losses dominate, then I am going in the wrong
direction. Thanks for the advice.
Dudley - WA1X
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