Spectrum analyser and resolution bandwidth For the preliminary part of a lab I had to do, I was asked the following question:


I get how to do 1.1, but with 1.2, I really don't get what's going on; I really would've thought that the resolution bandwidth would be equal to the bandwidth of the low-pass filter.  Furthermore, I'm pretty sure a spectrum analyser has a variable band-pass filter in it, so I really don't get what's going on here.

Any help would be much appreciated.  For the record, this isn't part of an assignment or anything like that, it's not worth anything, it's just something that's bugging me.

Thanks.
This document is seriously awesome.  It gave me a good understanding of how spectrum analysers work in an easily understandable way.

http://literature.agilent.com/litweb/pdf/5965-7920E.pdf