There is one saving feature if AGC cannot be turned off.  If the signal to
noise is low, say 10db or worse, then you can at least mesaure S/N using
this technique.  The technique may not necessarily be of value at LF / HF
where noise level is likely to vary with propagation, but where noise is
equipment dominated is certainly allows accurate measurements to be made.  A
few years ago I made propagation measurements on microwave beacons using an
8 bit A/D (before programming soundcards became easy) and used S/N of the
carrier in 3kHz as a measure of signal strength.

Andy G4JNT

Forwarded from Rik Strobbe:

A software team from the Belgien amateur radio society UBA has developed a
programme that can be used to register the fieldstrength measurements. All you
need is a PC with Win95/98 and a soundcard. The audio output of the receiver
is fed to the input of the soundcard.

AGC (which is present in most amateur receivers) will make such measurements
almost useless (unless the AGC can be disabled).

Please correct me if I'm wrong...

73, Johan