[CQ-Contest] RE: Receiver tests

Bob Wanderer aa0cy at quadnet.net
Thu Mar 20 21:34:30 EST 2003

Noise/Com in Paramus, NJ also makes the noise
generator/notch for performing NPR.  It's probably less
expensive than HP/Agilent, but probably more expensive than
hams would want to spend.


-----Original Message-----
From: cq-contest-bounces at contesting.com
[mailto:cq-contest-bounces at contesting.com]On Behalf Of
Sent: Wednesday, March 19, 2003 6:16 PM
To: cq-contest at contesting.com
Subject: [CQ-Contest] RE: Receiver tests

Eric and the list,

The testing you have described is called "Noise Power
Testing" and the
figure of merit is the NP Ratio or NPR.  This type of
testing is many
decades old and has been used in the communications industry
for testing
multiple channel equipment, including radio receivers.
Basically, the band
of interest is filled with noise while one channel is
notched out, or free
of noise.  The radio is tuned to the clear channel and the
noise power is
then increased until the noise floor of the radio is
degraded.  Some simple
arithmetic then calculates the figure of merit.

In the early 70s I was involved with the design and
construction of low
power, channelized SSB receivers.  One of the specifications
which my
customer required was a certain NPR.  I obtained the
equipment and performed
the test many times as each receiver design progressed.  The
NPR test is an
excellent way to optimize such parameters as the mixer and
product detector
drive levels and waveforms.  Also, these receivers used 3rd
order PLLs for
the LO injection and the loop parameters could be optimized
by watching the
NPR as break points were moved.

A couple of years ago I was able to purchase a noise
generator designed for
NPR testing on eBay.  They are made by the Marconi Company
and can be picked
up for $200 or so.  HP also makes equipment, but it's rather
expensive.  The
band stop filters used for notching out the noise are much
too wide for our
purposes, but it's a simple matter to build a quartz narrow
band stop filter
with crystals.

I have done this and have tested a few radios.  The big
problem here is that
it's not easy to relate NPR to 3rd order IMD tests.  Maybe
mathematician on here could work that out.  I'd be happy to
give him the
references needed to do the math.  There are books and
articles. etc.

One day when there is not so much to do, I'll continue this
study of radio
NPR measurements.

George, W2VJN

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