Here's how to determine when your C-L-C T-network antenna tuner's
output capacitor (or if you choose, its input capacitor), is fully
meshed -- without opening the box.
You need a multimeter (like my Radio Shack DMM) or an impedance
bridge that can measure capacitance at a low frequency, preferably
below 1 MHz.
Measure between the "hot" and "ground" terminals of the output
(antenna) end of the tuner. Crank or switch the tuner's inductor all
the way down to its smallest possible inductance, which would be at
the end or the extreme setting that you use for the highest
frequency. The minimum inductance of the coil is probably around one
microhenry. At 1 MHz or below, this inductance has a reactance of
about 6 ohms or less. This reactance is negligible in comparison
with even the smallest possible reactance of the output capacitor of
a typical antenna tuner. The maximum capacitance of one of these
cap's is typically 240 pf; the reactance of 240 pf at 1 MHz is -663
ohms. Therefore, with your meter, you are effectively looking
directly at the capacitor.
Now turn the knob on the output (antenna) capacitor and watch the
meter or bridge to find the maximum C.
-Chuck, W1HIS
|