Hi,


I suggest you google some documents on spectrum analyzer fundamentals. The documents by Agilent are very helpful.

A spectrum analyzer is similar to an AM receiver. Anyway RBW is the resolution bandwidth and if you are familiar with receiver design (which is basically what a spectrum analzyer is), it is your channel filter bandwidth. i.e. it is the filter after the frequency translation. A narrower RBW will lower the noise floor potentially making your signal more clear. After the RBW filter, the signal is basically amplitude detected using some kind of rectifier. And following this rectifier is another filter which is basically your VBW filter. Reducing the VBW is akin to averaging the signal power. It does not reduce the average level of the signal or noise, but it removes all the large spikes you see in the noise also potentially making your signal clearer. So to sum up, reducing RBW lowers the noise floor, while reducing the VBW smooths out the noise.

Modern high-end spectrum analyzers are implemented quite differently. Basically they can digitize the signal much sooner, but the basic principles of RBW and VBW are the same.

Anyway like I said you're much better off reading some of those Agilent documents on spectrum analyzer fundamentals.


cheers,
Aaron

raja.cedt wrote on Aug 19^th, 2010, 10:39pm:
Not correct.

Noise marker mode in Spectrum Analyzer where dBm/Hz or dBc/Hz is displayed has no relation to RBW directly.