Re: {Collins} 75S NPR Measurement

Hi Paul,


I have just rejoined the reflector and would like to thank you and Don for
mentioning my NPR article and posting the link. The article has also
appeared in QEX, March/April 2015.


To address your question: "How would 75S testing deviate from the
conventional receiver method that he describes?" From my understanding of
the 75S architecture, it would not deviate at all. I would select the 2.1
kHz mechanical filter (whose passband fits nicely into the 3 kHz notch of
the  bandstop filter in the noise generator), connect an RMS voltmeter to
the audio output, tune the receiver to the centre of the notch and advance
the noise loading until the audio output rose by 3 dB. I would then
calculate NPR using the procedure in the article.
This approach would stress the entire signal chain, and yield an NPR value
which could then be compared to data taken from other conventional
The following standard test channel frequencies are compatible with the 75S:
1940 kHz
3886 kHz
7600 & 11700 kHz (with special 1st LO crystals)
If a list member living in the Vancouver BC area would like to bring his 75S
or KWM-2/2A to my lab, I would be very glad to run an NPR test on it.


Best 73,


North Vancouver, BC, Canada 




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