[Premium-Rx] Noise Power Ratio Testing of Radio Receivers

[Adam Farson]

For the past 3 years, I have been researching the possibilities of using
noise-power ratio (NPR) testing – a test method long employed in the telecom
industry – as an alternate performance-evaluation technique for HF, MF and
LF receivers. In this test, a noise-band containing a deep, narrow notch is
applied at a fairly high power level to the DUT input. The DUT is tuned to
the centre of the notch, and an IF bandwidth somewhat narrower than that at
the bottom of the notch is selected. NPR is the ratio of the noise power in
the notch to that in a bandwidth equal to that of the IF well outside the
notch.

The incident noise provokes active and passive IMD, and reciprocal mixing,
in the DUT. These effects appear as added noise which appears in the DUT’s
IF channel. The NPR test emulates a band packed with very strong signals.
Thus, it is felt that this test is a better method for assessing receiver
performance under these extreme conditions than a narrow-band (e.g.
2-signal) test.

For several months, John KE5QAP, who is also a list member, and I have been
collaborating on this project. John adds that has tried all the traditional
tests:  IMD, second and third order, phase noise, blocking, MDS and so
on.  Still, the question is open as to which ones are the most important. 
The NPR test gives one number that combines many of these tests in a
meaningful way.

I have had an article on NPR testing of HF receivers published in RSGB
RadCom, December 2012, pp. 42-45. In addition, there is a relevant paper on
my website, which incorporates test results for a number of transceivers and
receivers:

http://www.ab4oj.com/test/docs/npr_test.pdf 

http://www.ab4oj.com/test/main.html#NPR 

Recent presentation at the North Shore ARC, North Vancouver, BC: 

http://www.nsarc.ca/hf/npr.pdf 

Best 73,
Adam, VA7OJ/AB4OJ
North Vancouver, BC, Canada
http://www.ab4oj.com/