Well, actually, I think that contest conditions are very similar to the NPR
test. More particularly, the NPR test is a far more
accurate representation of what's happening on the band during a contest,
compared to a two-tone test with just two signals on the
band!
And while some of our current receivers might look pretty awful, designers
aren't going to work on improving them until they see
some market interest.
Thanks for all the good info, Al!
-- Eric K3NA
-----Original Message-----
From: al_lorona@agilent.com [mailto:al_lorona@agilent.com]
Sent: 2003 March 19 Wednesday 13:39
To: eric@k3na.org; cq-contest@contesting.com
Subject: RE: [CQ-Contest] receiver evaluations
One more thought...
The NPR test applies best when the interfering signals are on all the time, all
at the same time. This would be the case in, for
example, a cable TV system, or a satellite downlink system. That's what the
notched noise is trying to replicate.
In a ham receiver, the interfering signals aren't usually on 100% of the time
(in other words they have a duty cycle less than
100%), and they aren't usually packed solid across a band-- although a crowded
contest is the closest we come to that condition.
Therefore, the NPR test would really be a much-worse-than-worst-case test, and
we would probably be appalled by the measurement
results of our receivers.
The NPR signal really re-creates the conditions that we would have if every ham
in the world picked a different frequency on 20
meters (except for 14.025 MHz) and then went key down for 60 seconds while you
tried to listen for a weak signal on 14.025 MHz. Can
you imagine? Not very realistic.
Regards,
Al W6LX
-----Original Message-----
From: Eric Scace K3NA [mailto:eric@k3na.org]
Sent: Tuesday, March 18, 2003 1:06 PM
To: Cq-Contest
Subject: [CQ-Contest] receiver evaluations
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
---------------------------------------------------------------
The world's top contesters battle it out in Finland!
THE OFFICIAL FILM of WRTC 2002 now on professional DVD and VHS!
http://home1.pacific.net.sg/~jamesb/
---------------------------------------------------------------
_______________________________________________
CQ-Contest mailing list
CQ-Contest@contesting.com
http://lists.contesting.com/mailman/listinfo/cq-contest
|