[R-390] Distortion on MGC mode and another question on sensitivity

[n4buq at knology.net]

Thanks for the replies about the MGC distortion.  I was thinking someone 
had posted a while back that the R390* radios should not overload on strong 
signals, period, but I suppose that's only in AGC mode.

Another question:  When I'm testing for sensitivity, I'm looking for the 
signal level that will result in -7V on the Diode Load; however, when I 
connect the signal generator, there is atmospheric noise that is introduced 
before I inject any signal which results in a few volts on the Diode Load.  
Is it correct to increase the generator's output level to -7V total and 
read the sensitivity from there, or should the signal generator result in a 
7V increase over the existing noise?  In other words, if I'm getting -3V in 
atmospheric noise, then do I take my sensitivity reading at -7V or -10V?

Part of this problem is the rigged-up mechanism I have for connecting the 
generator to the receiver.  I'm in the process of making a housing for the 
attenuator and feeding everything with coax thus eliminating the 
little "antennae" I introduce with the current setup.

I assume the -7V reading is accurate (or at least more accurate) if the 
test is done in an RFI-proof environment with a perfect signal generator 
that doesn't leak.  Lacking those two things, what is the proper way to 
measure this?

Thanks again,

Barry