[CQ-Contest] receiver evaluations

Eric Scace K3NA eric at K3NA.ORG
Tue Mar 18 16:06:01 EST 2003

   For some time now, ARRL and others have included in their collection of receiver performance test the blocking dynamic range and
two-tone 3rd-order IMD, using two signals with some spacing such as 5 or 20 kHz.  Of course, two strong signals doesn't emulate much
of the real world.

   I recall a variation of this test that was used by AT&T to evaluate performance of multi-channel radio receivers used to carry
large quantities of telephone channels.  Naturally, one did not want a strong signal in one telephone channel to contaminate the
signals being carried in other channels on the route.  The test was performed as follows:
   -- instead of two signals being applied to the receiver under test, a broadband noise was applied.  The noise was modified by
notching out the bandwidth for one channel; i.e., essentially no noise in the notched channel.
   -- measurements were made in the channel corresponding to the notch.
   -- noise power to the receiver was increased until the point at which the measured channel started to exhibit degradation (e.g.,
increase in the noise floor).

   This seems to be a more general test that corresponds more closely to what a contest receiver experiences on a crowded band;
i.e., LOTS of signals attacking the receiver across the band.

   Could those who are knowledgeable about receiver evaluation methodology comment as to whether such a test would be more likely to
accurately characterize the ability of a receiver to hold up against strong signals outside of the operating passband than the
two-signal test method?


-- Eric K3NA

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