FWIW,
RSGB Radio Communication magazine a while back showed how the caps on a
conventional T match could be made to operate simple shorting switches at
the extreme end of their rotation, thereby converting the T into an L match
(in either configuration, higher Z in or Out) thereby increasing the
operating range and efficiency.
I still use big old link coupled jobs myself. Look like out of the early
30s, work like a charm. Made out of stuff garnered from junk sales, cost
less than the knobs on the tuners some people use.
Jump the ladder line from one ATU to the other with an even older copper
and porcelain knife switch, looks like what was portrayed as operating
electric chairs in those old movies, but we may be going dangerously off the
thread here.......
73
end
Barry Kirkwood PhD ZL1DD
Signal Hill Homestay
66 Cory Road
Palm Beach
Waiheke Island 1240
NEW ZEALAND
www.waiheke.co.nz/signal.htm
----- Original Message -----
From: Tom Rauch <w8ji@akorn.net>
To: <W8JI@contesting.com>; Amps Reflector <amps@contesting.com>; Jon Ogden
<na9d@speakeasy.net>
Sent: Thursday, 21 June, 2001 4:26 PM
Subject: Re: [AMPS] Review of Antenna Tuner from Dayton
>
> > Well, my problem was that my capacitance on my old tuner was pretty much
> > maxed out. I couldn't add more. Believe me, I remember our
conversation.
> > But when the cap is fully meshed when it arcs, there's not a lot one can
> > do.
>
> Unfortunately wider spacing increases voltage at the same rate as
> the wider spacing increases voltage rating when as you are using
> far less than optimum capacitance. You really gain nothing, for a
> certain physical size capacitor, unless the antenna impedance is
> very high. Power handling can actually decrease by increasing
> spacing at low and moderate antenna impedances, for a fixed
> capacitor length.
>
> The solution is to use enough capacitance to have operating Q as
> close to minimum as reasonably possible. The ARRL Antenna
> Handbook comes with some nice software for looking at tuners, it
> is interesting to play with values and look at voltages (I use a Lotus
> 123 spreadsheet I wrote).
>
> You'd be amazed at the problems T networks have on 160 and 80
> when matching low load impedances and capacitive reactance
> loads when the tuner C is too low.
>
> My ATR 30 by far outdoes my old KW Johnson Matchboxes, which
> are now all stashed away in a storage building. Of course I have no
> idea how the latest Hrevnek? tuners are, I've only seen the units
> from Viewstar and Vectronics. It might be much better engineered
> than past products.
>
> 73, Tom W8JI
> W8JI@contesting.com
>
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