[R-390] R-390A sensitivity measurements

[James A. (Andy) Moorer]

Given that a 50 ohm resistor has a thermal noise of .0142 microvolts (at 
room temp, BW of 1 KHz), it is hard to see how adding .01 microvolts can 
cause a 10 dB change in the reading. Even if the input is 25 ohms, the 
thermal voltage will still be .010 microvolts.

See my "noise and sensitivity page" at 
http://www.jamminpower.com/main/noise.jsp

I think we are doing this measurement wrong, but I haven't managed to figure 
out what the right way of doing it is. I did publish (with permission) an 
article by Dallas Lankford on the measurement process where he obtains 
numbers that are more believable. I understand that we do see the meter 
change by 10 dB, but I think there are other explanations for that. For 
instance, the R-390A is not very well shielded. Neither is the URM-25. Is it 
possible there is some leakage via a route that is external to the antenna 
input? I dunno, but I know we can't get more sensitive than the thermal 
noise. It doesn't take many electrons rolling through the ether to show up 
as a 10 picovolt  input.

James A. (Andy) Moorer
www.jamminpower.com