Hi, Eric,
The test you described is called the Noise Power Ratio (NPR) test, and it is
used more and more to simulate the multi-carrier conditions that an amplifier
is likely to see. It is primarily for transmit and receive amplifiers working
at high frequency, but I don't know if it has ever been applied to the entire
receiver, RF-to-AF.
You need a very good signal generator to create that kind of a signal. The
noise has to be wideband and perfectly flat, with sharp corners. The notch is
very difficult to create. You want to get a notch about one channel bandwidth
wide, which in a typical ham receiver would be about 2.5 kHz for SSB or 500 Hz
for CW. An analog filter can be used, but it is far from ideal. Nowadays, an RF
generator with arbitrary digital modulation is used and the NPR modulating
signal usually has to be downloaded from a computer into the generator. The
signal is usually in I-Q; that is, there are two channels which are combined to
give you the necessary amplitude-and-phase-versus-time waveforms that describe
the spectrum required. You can see a glimpse of what I'm talking about at:
http://eesof.tm.agilent.com/docs/adsdoc15/examples/tutorial/NoisePowerRatio.html
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
|