[ARC5] Receiver input impedance.

[Ian Wilson]

Robert is correct about the input trimmer: this is in parallel with the
tuned circuit,
and the antenna connects to that through a small fixed capacitor. My bad.
The
impedance of the input at resonance is not determined by the grid leak
resistor
of the first tube, but by the parallel effective parallel resistance of the
coil, namely
2pi * L * Q. Guessing that the tuning capacitor is around 300pF at 500kHz,
then
the coil inductance will be on the order of 350uH. With a Q of 50 the
equivalent
parallel resistance will be around 55k ohm.

73, ian K3IMW