MF,
Today i've build a box for matching different antenna impedances to the
50 Ohm output of my PA. An amperemeter is inserted in the coax output,
so the antenna current can be measured directly, in certain antenna
configurations. The circuit is of course nothing special, just a switch
with many steps and a transformer with many taps :-) The amperemeter is
analog, class 1.5 (made in England, about 40 years old) and i like the
rapid moving of the needle (could be a bit slower though, will add some
C...).
Now it was possible to accurately measure the resonance of my antenna
system using a fixed coil, it is actually 475.5 kHz, exactly the middle
of the band. However the Q is very high, the antenna current drops by 3
dB at 472.25 kHz and 478.25 kHz, i.e. the -3 dB BW is 6 kHz and so the
(loaded) Q is 79. Thus i think i will need some kind of reactance
compensation and intend to use a series configuration of a L and a C,
also added by a stepped switch...
The impedance switch will allow to match the full size dipole when
beeing /p. I will do this test in the coming days.
73 and funny MF times.
Stefan/DK7FC
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