[R-390] R-390A sensitivity measurements

[DJED1 at aol.com]

No, the 82 ohms goes in parallel with the nominal 125 ohms of the radio, 
resulting in 50 ohms as seen by the generator (procedure from URM-25 manual) In 
this case, the generator is correctly terminated in 50 ohms, and connected 
directly to the receiver terminals.
The 75 ohm resistor goes in series with the 50 ohms of the generator, giving 
a 125 ohm impedance for the radio (procedure from MIL-SPEC for R-390).   In 
this case, the generator is not terminated in 50 ohms, but the voltage division 
between the 75 ohm resistor and the receiver impedance give the correct 
voltage at the receiver terminals. 
 Either approach allows you to use the generator meter to correctly read the 
voltage across the receiver terminals.   You can use both a series and shunt 
resistor to provide the correct impedance to both the generator and the radio, 
but then you have to correct the meter reading to get the voltage across the 
receiver terminals.   I haven't tried this yet, but doubt that it will make 
much of a difference in the results.
Ed