"Chris BONDE" <firstname.lastname@example.org> wrote:
>I think that I remember something from long time ago. Twin lead was
>inexpensive, coax was expensive, dipoles multi dipoles and
>non-resonant dipole were fed with twin lead or home-brewed twin
I remember this, too; and it remains true today; doesn't it?
>Now, I think that this was terminated by an open air coil with multi
>taps outside of the house. The tapes were moved for the best
>connexion via two pieces of short length coax to the tuner or pie
>net work next to the Tx. Is this correct?
I don't remember hearing about an open-air coil outside the house;
and, anyway, an open-air coil outside seems to me a bad idea. It'd
be unsafe; insects and small birds would nest in it (Yeah, I know,
not for long; but there'd be residue.); and, where I live, it'd be
full of snow and/or ice for much of the winter.
So let's assume that we enclose it. Changing bands would require a
trip outside (Bummer!) unless you had a remotely operable switch or
Now removing my Grinch hat....
I have a very nice remote antenna tuner, made by RCA apparently for a
military or commercial application, and which I picked up as
surplus, which does more or less what you describe. It's in a large
weather-tight metal box with a removable, gasketed, access door and
two big beehive ceramic feed-throughs for connecting balanced
open-wire line to go to the antenna.
Inside is a 3-inch-diameter tank coil with several balanced pairs of
taps, and a big ceramic rotary switch for selecting a tap-pair. The
taps can be repositioned on the coil manually, and continuously
rather than just discretely, with a screwdriver. The switch is
operated by a stepper motor.
An additional deck of switch contacts selects a resonating capacitor
for each pair of coil taps. The capacitors are big ceramic
transmitting types. A screw-terminal strip is provided for changing
capacitors. (There's enough room in the box that I've considered
installing one or more continuously variable capacitors, for speedier
tuning. However, a continuously variable capacitor is not strictly
necessary, because the coil taps are continuously variable.)
The input to this tuner is by a single coaxial cable and is
link-coupled to the big tank coil. I suppose that you could connect
the coax shield directly to the midpoint of the tank coil, and the
coax center-conductor directly to a point on one side of center;
however, link coupling is superior because it provides excellent
I haven't used this tuner yet, but some day....
73 -Chuck, W1HIS