On 3/24/2015 2:28 PM, tedc@nucleus.com wrote:
the band. A monimatch located just before the
Capacitor with the appropriate motor driver circuitry
will automatically adjust the capacitor for the best
match. My design is for a single tower but should
A better idea is use a phase detector. This can be
made from a directional coupler (not a
directional detector) connected to the inputs of
an Analog Devices AD8302, which in turn drives an
integrator that drives a DC motor. Insert a 90
degree phase shift in one of the two AD8302 inputs,
consisting of a pi network with 1675 pF shunt caps and
a 4.2 uH series inductor. (Note that the reactance
of these components is 50 ohms at 1.9 MHz)
Put 50 ohm terminations with blocking capacitors at
each AD8302 input. The motor will be caused to turn until the
drive impedance becomes resistive, which is what you
want. With this system you don't need a pot connected
to the motor shaft to sense where the capacitor is.
It will just converge on resonance automagically.
This eliminates "hunting" algorithms that try to
find the dip in SWR. Amazing that these are still
in common usage.
Rick N6RK
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