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?
Thanks.
-- Eric K3NA
|