IF the receiver input is protected by an AGC
diode, any signal that exceeds the RF AGC
threshold will turn on the AGC diode which
will greatly alter the 'measured' input impedance.
To properly measure input impedance, it is necessary
to use a test signal level that is below the RF AGC
threshold OR, disable the RF AGC and ensure that
the test signal level does not exceed the dynamic
range of the input device.
de Tom N4KG (receiver design engineer)
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