Yes Don, I find folding back the top loading easy. Then using a roller
inductance to find the value needed to match it followed by the last stage of
measuring the inductance and recreating it using Airdux or similar works well.
73 Clive GM3POI
From: Don Kirk [mailto:wd8dsb@gmail.com]
Sent: 20 September 2018 07:51
To: Clive GM3POI
Cc: topband
Subject: Re: Topband: Toploaded vertical - SWR
Hi Clive,
Nothing wrong with the hairpin as you mentioned which I really consider to be a
high pass L network (which N3QE eluded to) in which the L network capacitance
is provided by the antenna (you have to actually shorten the antenna from its
resonance dimension in order to provide the required capacitance, and it is a
precise value of capacitance you need in order to provide a "perfect match" in
conjunction with the precise value of hairpin inductance that's required for
the "perfect match").
Great discussion with numerous approaches.
73,
Don (wd8dsb)
On Wed, Sep 19, 2018 at 1:46 PM Clive GM3POI <clive@gm3poi.com> wrote:
What I don't understand is why would you use more components than needed.
Why a capacitor (possibly vacuum). What is wrong in using a hairpin which
also DC shorts the vertical to ground. A combination of hairpin size and
top loading will give you 1:1 at your favourite 1.825 or anywhere else.
Perhaps WX0B's article needs a reprint in the NCJ. It really is simple just
a few microhenries of inductance and you are done.
73 Clive GM3POI
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Don Kirk
Sent: 19 September 2018 17:29
To: Herbert Schoenbohm
Cc: topband; ash.kf5eyy@gmail.com
Subject: Re: Topband: Toploaded vertical - SWR
>
> Herb (KV4FZ) mentioned an L network, and that is what I always use. Very
> simple, and you just plug you're measured complex impedance values (at the
> frequency you want to be resonant) into one of the many online L network
> calculators to determine the amount of inductance and capacitance required
> for the L network. I normally just wind my own coil for the inductance,
> and use high voltage silver mica caps for the capacitor.
>
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