Topband: Input Impedance of the FT1000/S-Meter Calibration issues

[Tod - ID]

Sinisa:
 
I have found your reflector comments useful and interesting.

You said, ".. No, it cannot be fixed this way. This will only ensure that
constant power is delivered to the  external attenuator, but the original
problem repeats itself  between external attenuator and RX input. "

This part of the S-Meter thread began with Eric, K8LV, posting a note on his
effort to measure the input impedance of the FT1000 receiver. If I
understood correctly, Eric asserted that " S-meters essentially measure the
voltage present at the RX input". 

Somehow I have the idea the S-meters are indicating, not measuring, the
output differences between two inputs to a 'black box of non-passive nature'
that exists ahead of the point at which the S-meter is positioned in the
electronic circuit. Perhaps there is real measurement, but I am not sure
just what is purported to be measured -- for that matter, I am not
absolutely certain there is complete (or even partial) agreement on what the
different readings of an S-meter are supposed to represent.

Eric's measurements suggest that the 'black box' I refer to has variable
performance characteristics depending upon the selections made while using
the receiver and that these changes are sufficiently significant to make the
S-meter indication vary even though the input signal remains "constant".

Sinisa, When you say "..it cannot be fixed this way.." should I interpret
that to mean that it can be fixed, but not the way suggested or that it
cannot be fixed at all. (I am not actually sure what we are fixing so maybe
someone can clarify that).

Tod, KØTO