Dear Walter,
I have seen your contribution rather late, because I have been travelling.
My opinion is that circuit A allows tuning the whip to resonance and matching
it to the amplifier, by changing the number of link turns. Therefore tuning is
very sharp.
In circuit B (which I have seen for the first time) the coupling between the
amplifier resonant circuit and the aerial coil will be much tighter. Tuning
the plate capacitor will even influence the aerial resonance, therefore only
few taps are needed for the whip. On the other hand I do not see any means to
match the whip (plus aerial coil resistance) to the amplifier. Obviously this
has been omitted to simplify the circuit. I guess the load resistance of the
amplifier will be lower than optimum, hence the broad tuning characteristic.
HW?
Happy New Year!
73 Ha-Jo, DJ1ZB
"Walter Blanchard" <[email protected]> schrieb:
It's a bit late for Christmas puzzles but try this one:
Circuit A is the usual antenna tuning cct for a short highly reactive whip. It
has the advantage that the antenna tuning inductor can be a long way away from
the PA.
Circuit B has been widely used for HF walkie-talkies using a short whip. Only
one coil is needed because the end of the antenna can be brought right onto the
PA board.
Puzzle:
The tuning coil in A tunes very sharply; you really need a
continuously-variable inductor.
That in B tunes quite flatly and you only need a few fixed taps.
Why?
Incidentally, are they really the same circuit?
Happy New Year!!!
Walter G3JKV.
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