Dave_Richardson said:
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RE: Portable LF ATU article by G3LDO RadCom December 2003
In another posting, which I unfortunately deleted by mistake, it was
suggested use of the above for matching to "short" antennas.
I'd be very grateful to hear from anyone who's build this ATU and got it
working satisfactorily.
I can't get the LF Loading Circuit section of mine to tune-up at all, it's
completely flat with any values of selected C.
I suspect it's all down to my fabrication of the Loading Coil, ferrite
used etc. so it'd be very helpful if I knew at least the value of inductance
I should be aiming at for this particular cct. then I can mess about with
number of turns, ferrites and so on...
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I had to have several attempts to get coil tuned and matched. I filled the
three-ferrite former with wire but it was still too high in frequency and I
had wind a further layer on top covering half the former. If the frequency
is too high it falls into the broadcast band, which is filtered out by the
G0MRF rf amplifier filters .
The quality and composition of ferrites from old transistor radios varies
considerably so the only way to manage all these unforeseen variables is to
put lots of tappings for both the antenna connection and the ampl;ifier
connection (as Mike Dennison will attest from the early 73kHz receiving
experiments). Tune up on the large signal on 138kHz initially.
Regret unable to measure the inductance of the coil.
Peter G3LDO
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