|[AMRadio] Johnson Match Antenna tuner|
Mike Dorworth K4XM
k4xm at arczip.com
Sat Aug 7 14:12:26 EDT 2004
> Rivpapa1 at aol.com wrote:
> > What is the proper adjusting procedure for using a Johnson Matchbox ant
> > tuner..There are two controls..tuning and Matching...Which is adjusted
..Well her is my $0.02 worth. Since I have owned 6, 2 bigs, 4 littles and
used them for years I will add this little bit of information. The Left knob
resonates the circuit, the right knob is a dual, dual differential which in
theory should never change it's capacity. Actually it does not work quite
like the idea calls for. It's job is to provide a potentiometer effect that
would be the same as tapping the antenna on the coil turn by turn from the
high impedance to low impedance end of the standard parallel tuned circuit.
In practice, the turning of one sorta effects the other plus the fact the
input link is fixed and stuff is reflecting every where.
The main idea is to get the reflected power to zero, the old time highly
frequency sensitive swr bridge makes it a hard job to say the least. Since a
watt or two can make it look like everything is being reflected.
I find that the easy way is to use a modern toroid based wattmeter and
twiddle knobs for minimum reflected power without regard for output power,
then I tune on all bands of interest and make the settings on the provided
charts. If one band is tricky or flaky, I change the feedline length until
it loads smoothly on all bands. I have never found an antenna that can not
be tuned by the Johnson after adding or subtracting some feed line. You
start with the notion it " WILL WORK" and then you make it so.
Also if you are using a boat anchor, hmnn, don't we all? Then the rig must
be tuned to a dummy and left alone and the matchbox tuned. If the rig is not
tuned first and you get to twiddling knobs it will be most frustrating..
Hope this helps.. 73
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