bravo John, and Don...that's a keeper!
w5xz
On Thursday, May 30, 2019, 10:32:36 AM CDT, n7wbjohn . <n7wbjohn@gmail.com>
wrote:
I found the article here, http://www.iz5cml.it/forum/trap.pdf
if it doesn't work, I got a copy I can send you.
73 de John N7WB
On Thu, May 30, 2019 at 4:19 AM Don Webster via Antennaware <
antennaware@contesting.com> wrote:
>
> David,
>
> Yardley Beers, W0JF wrote an article in the August 1987 issue of Ham Radio
> about a "new approach to designing trap antennas". It dealt with the design
> frequency of the traps being about midway between the two bands.
>
> I built a 3 element yagi for 12 and 17 meters using his approach and it
> works very well. You have to adjust the length of the elements to
> compensate for effects of the traps.
>
> Don
> K9MUF
>
> -----Original Message-----
> From: David Gould <dave@g3ueg.co.uk>
> To: antennaware <antennaware@contesting.com>
> Sent: Wed, 29 May 2019 9:35
> Subject: [Antennaware] Trap design
>
> Yes, I know traps are a compromise and some people don't like them, but
> my feeling is that it is often the design and construction that are the
> main problems.
>
> I plan to build one for 15m (for a 15m/20m elevated vertical) using a
> heavy duty doorknob capacitor and small diameter copper tube for the
> inductor, which should optimise the construction issue.
>
> Question 1) What should the design frequency be? I vaguely remember
> reading somewhere that the design freq should **NOT** be the middle of
> the higher freq band (eg 21.225 in this case) but on some other freq
> somewhere between 21MHz and 14MHz. I have done several Google searches
> and cannot find any references, in particular I would like to know the
> reasoning behind doing this, and how using such a mid-freq affects the
> length of the two parts of the antenna?
>
> Question 2) Are there likely to be any issues measuring the resonant
> freq of a trap using a RigExpert AA-54 analyser, or is there a better
> way? Again I vaguely remember reading that a dip oscillator is the
> best way, but I don't have access to one.
>
> 73,
>
> Dave, G3UEG / K1MDX
>
>
>
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