On Wed, 2008-05-07 at 11:41 -0400, Bill Ames wrote:
> Then the question would be, if I selected the right materials (torrid and
> wire) and a proper design (number of turns, etc.) then would this be the
> least loss matching device? If yes, what material and design would be best?
>
> Bill
>
> KB1LG
>
Go large on the core and wire. If it doesn't get hot with a KW going
through, the losses will be small. But it won't take care of the
reactance from being away from the resonant frequency of the antenna.
And that reactance upsets the output device in the transmitter causing
less than optimum output.
The toroidal transformer also gives only a few impedance ratios (square
of the turns ratios) which limits the quality of the match achieved in
the real world.
Remember too that unless your signal is truly at the noise level or
below (as in EME operations some times), a dB change in radiated signal
is only going to make a dB or less change in signal to noise ratio at
the other station. Propagation varies a whole lot more, and often
randomly. And a dB change is 21% down in power. Whether your antenna
matching scheme is 79% or 92% efficient won't be detected at the other
end of any HF propagation path. And the higher efficiency won't give you
an edge in the DX pileup halfway around the world.
I still like the link coupled tuner with provisions for making the
antenna side series tuned for low impedance loads and parallel tuned for
high impedance loads with maybe taps on the parallel tuned connections
for mid impedance loads. Its a technique that can have low losses (my
BIG tuner uses a coil of 1/4" wide edge wound copper strap. Its too big
though). And though it may take a different tuner for wide ranging
bands, I've tuned such things as a 75 meter double extended zepp (made
of #10 copper weld, it was only 95 meters long) from broadcast band
through 144 MHz with such link coupled tuners. And I've made many
contacts on 6 and 2m with that wire. It had gain on all bands from 80
meters and higher (frequency) though at VHF there are nulls between the
many lobes.
For a compendium of link couple tuners you could down load a Collins
32V-2 manual for the Collins Collectors Association web pages. That
manual has a few pages on tuners.
Tuners also add the the RF selectivity of the receiver reducing intermod
from broadcast stations and reducing the transmitter spurious outputs
and so reducing interference.
73, Jerry, K0CQ
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