[R-390] OT: IMD distortion measurements

[Paolo Mantovani]

Hello everybody and happy new year!

I would like to better understand IMD distortion measurements. The 
manuals of a couple of receivers I own (Siemens E311 and R&S EK-07) say 
the "resistance to intermodulation" must be:

"Intermodulation <= 10%, with an unmodulated useful input of 50uV and an 
interfering input of 15mV, modulated m = 50% and 20kHz away" (E311)

and very similarly for the EK-07 but 50mV instead of 15 for the 
interfering input, this possibly meaning a stronger resistance.

That means to me that I should tune the useful signal and measure a 
level of modulation lower than 10%, that is generated by IMD distortion 
with the interfering input which is modulated 50%. What I can't 
understand is if and how this compares with the two-tone IMD level 
measurement method, when one injects two unmodulated signals of equal 
power and measures the level of IMD products.

I did not found any source of information on the above measurement 
method, any help would be appreciated.

Thank you
Paolo