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

[Michael O'Beirne]

Dear Adam

Many thanks for all that.

Perhaps it is also time to re-visit the famous embargoed article by Sosin, 
Marconi's Chief Scientist in the Marconi house mag, Point-to-Point 
Communication in or about 1972 in which he tried to devise a method of 
testing hi-grade receivers using an all-embracing formula (which frankly I 
never understood) that took in IP3, front end preselection, reciprocal 
mixing effects and much more to try to establish a "failure factor" - ie the 
factor by which the receiver fell short of the perfect receiver.

As I recall, mathematically he appplied a barrage of frequencies and input 
levels to the receiver to simulate the live mass of signals that appear on a 
profesional aerial and derived how the receiver would react to such an 
environment rather than the  somewhat unreal standard two-signal IP2 and IP3 
test.  His analysis demonstrated the continued value of traditional LC 
preselectors, albeit that in his time, and still now, tracking preselectors 
werw and are a very costly way of doing things.

In a related sort of way there is also a debate as to what input levels 
should be applied to an IP3 test to establish a valid test.

I personally distrust searching for an IP3 product at the miniscule MDS (3dB 
s+n/n).  At best one should be measuring this with a true RMS voltmeter, but 
how many of us have one?  In contrast, going for a 10dB s+n/n ratio should 
be more accurate since most average reading voltmeters will be ok.

But even then, the levels are unlikely to be "teasing" the switching diodes 
in the half-octave filters and elsewhere.  And the levels can be high.  Even 
on my small Wellbrook Loop feeding a spectrum analyser, levels well in 
excess of 10mV are to be expected from the usual broadcasters and they are 
miles and miles away from me. I dread to think what would happen if I had a 
kW down the road.

73s
Michael
G8MOB

----- Original Message ----- 
From: "Adam Farson" <farson at shaw.ca>
To: <premium-rx at mailman.qth.net>
Sent: Monday, December 03, 2012 5:46 PM
Subject: [Premium-Rx] Noise Power Ratio Testing of Radio Receivers


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/