[Elecraft] 250 Hz and 400 Hz Filter Measurements

[Phil & Debbie Salas]

"Is anyone else here familiar with notched noise IMD measurements?? I only
used them a few times in the 80's, so my recall is limited."

Tom - This is the way we used to measure our analg FM and SSB microwave 
radios at Collins/Rockwell.  A broadband noise source with a very high-Q 
notch filter was injected into the transmitter baseband input.  We had notch 
filters at low, mid- and high baseband frequencies, though the highest 
baseband frequency was always the worst.  However, we were using pre- and 
de-emphasis to compensate the baseband signal.  We looked at total noise 
(normal KTB plus IMD) in the received channen associated with the notches. 
Since we knew the KTB noise floor, we could then determine the IMD noise. 
Brings back memories.

Phil - AD5X