As was previously posted, you need to slow down the sweep speed and/or narrow the resolution or video bandwidth, which may automatically slow down the sweep speed. The filtering is done digitally in most modern SAs, and this takes time, so the sweep is slowed down to accomodate this. You don't want to go TOO narrow otherwise you'll lose some amplitude accuracy. Narrowing the span of the sweep will also help.
If the unit has a way to do a peak hold, or max hold, use that with a slow sweep (around 0.1 second per division) and leave it running for 10-20 minutes. All you can do is hope you catch a signal that pops up and stays there long enough to be captured. Any SA under a million dollars is a sampling sweep unit, as opposed to a real-time unit that can receive and display all frequencies at once. You don't have far to go. -127dBm is 0.1uV and I wouldn't expect any signal at that level or lower to cause interference with any system on 450 MHz. Bob M. ====== --- vintageaudio2004 <[EMAIL PROTECTED]> wrote: > I have a quick question for the group about the > noise floor of a > spectrum analyzer, hope that with the collective > knowledge and > experience somebody can help me out a bit. > > We have customer that needed a couple of site > surveys done, in order > to detect any possible interference sources on 3 > segments of 2MHz each > (we used the 200KHz/div screen span setting), in the > 455-465MHz > region. Surveys have already been completed, but the > customer is now > asking us to redo a few of the site surveys that > didn't catch any > interference because the noise baseline on the > instrument that was > used is -110dbm. The customer says he needs it done > at a noise floor > of -124dbm to make sure the frequencies are really > clean. > > Could anybody clarify how one does lower the noise > floor of the > analyzer? It was my understanding that the noise > floor is a intrinsic > characteristic of the instrument itself, and is so > to say a > measurement limit that cannot be varied without > external aids (or > maybe with a low-noise LNA?). But if one uses an > external amplifier, > wouldn't this also raise the site noise floor on the > analyzer screen? > Or if I am wrong, how could one lower the noise > floor of the > measurement in order to be able to take measurements > at lower levels? > Or is the noise floor also a function of the SITE > noise level per se? > > BTW, we used a IFR (Aeroflex) COM-120B during the > surveys, coupled > with the EasySpan II software to make the screen > captures. > > Thanks. > -Alex __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
