"Roy Lewallen" wrote in message
...
[...snip...]
If you're trying to measure the noise
coming from a receiver, it has to be considerably greater than the SA's
internal noise, or you'll never see it.


Assuming classical "noise" as we are all probably thinking...
First, a minor correction to the above "considerably greater", Roy. If the
EXternal noise is just 6dB above the SA's INternal noise (I guess 4 times
can be considered 'considerable'), then the resulting displayed value will
be only 1 dB higher than the incomming noise actually is. Noise power (when
combining in one receiver) simply adds. To see the math, think this way. A
1 dB increase amounts to 1.25 times the power. That extra 25 percent is one
fourth the original power. 25% of the power is 6dB down from the original.
SO adding some power which is -6 dB (or 25% the original) will raise the
total 1 dB.

However, The poster used the term "noise", but doesn't know the source of
his problem. His data hits can be caused by other than what we are thinking
is noise. It can be (sounds like since it recently started) spurious
signals in his channel OR it could be IM being caused from strong signals
getting into his receiver. The spurious in-band stuff could be narrow
signals or wideband. Typical CDMA signals behave much like simple wide-band
noise as we think of noise. A narrow band signal/spur is different.

From a later post I see that he is trying to measure some junk that has
appeared on the link frequency causing interference. In any case, the
front-end noise floor (noise figure) of the SA will determine how far down
you will be able to see and if it is not low enough, then you won't see the
interference. I can not comment on the Advantest sensitivity. If you have
access to a low noise amplifier of the type used in your system, it can be
used in front of the SA and *MAY* raise the sensitivity (lower the noise
figure/floor) enough to see yout interference.

Good luck. We've had a strange low level (around -123 dBm)spur on our
repeater input since last fall and can't locate it...wish I had lotsa time.
--
Steve N, K,9;d, c. i My email has no u's.