Rick wrote, in part:
> LB Cebik (W4RNL) has done an excellent job....
explaining Link Coupled Tuners. You'll find everything
you might need to know to either build up such a tuner,
or to modify an existing EFJ kW Matchbox, see:
http://www.cebik.com/link/link5.html
Circuit, component values, etc. all there. Much theory
is in the earlier four parts of LB's Link Tuner discussion.
> Most people probably won't tell a difference between the...
modified kW tuner box and the modified.
I don't agree, the modified tuner is MUCH easier to use
and tune's up very fast! The unmodified Matchbox can
be a chore to get tuned up correctly!
> What Annecke did was make the 50 ohm side switchable
> and added a 270 pF variable in series with the link.
What ought to be switch selectable is to tap to one of the five
turns of the Matchbox link coil as well as adding the series
tuning capacitor. I did that with mine and that circuit becomes
the first to adjust when using this modified circuit set up.
First, resonate the input circuit to the desired operating band/
frequency. I have taps to each of the five turns of my modified
unit. Turns out I have yet to use all five turns with the series
cap I have used. However, on 80 meters I use four turns
of the link; on the upper part of 75, 60 and 40 meters, three
turns; 2 turns on 30, 20 and 17; and only one link turn on up
through 10 meters.
I use my MFJ-259B in place of my transmitter to get the
Matchbox tuned up to frequency. Oh, should add that
on 30 meters I use the secondary circuit's switch setting
for 20 metes; and on 17m, the 15 meter position. 60 meters
required using the 80 meter selection in the secondary.
With the input resonated, watching the 259 go to lowest
vswr, then adjust the Matchbox Tuning and Matching
caps. You probably will have to go back and tweak the
link circuit cap since some reactance from the secondary
setting is coupled back into the input circuit. I can
always get very close to 1:1 swr with the modified circuit.
I gave up the onboard meter to find a place for the three
needed added control components. One rotary switch
to select the needed link turn; one rotary switch to
select the addition of an added capacitor in parallel
with the series input cap (needed for 75/80 meters)
and the series cap tuning knob.
Unfortunately, the components of the kW Matchbox do
not have high enough inductance or capacitance for
use on 160 meters; the band was not available to
amateurs back in the 50's when Johnson designed the
unit.
Very nice tuner. I use the open ladder line from W7FG
from the tuner out the to a doublet antenna which will
tune to any of the HF bands above 80 meters.
Hope of some use.
73, Jim KH7M
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