When making a
measurement to determine conformance to a
particular specification (GSM, for example), the
spec normally dictates the bandwidth in which it
is to be measured. Otherwise, you have to rely
on experience and knowledge of how the RBW
(resolution bandwidth) and VBW (video bandwidth)
affect the displayed signal. Most spectrum
analyzers come with a user’s guide that provides
some insight into how to set the instrument.
There are some good test notes on the RF Cafe
“Test Notes” page (1), including the classic
from HP (now Agilent).
The subject is too
broad to cover here, so please read some of the
notes on that page. One rule of thumb to
remember is that if a signal amplitude varies as
you change the RBW, then it has some bandwidth
to it (not a pure tome as with a synthesizer),
and if it does vary with RBW, then it has some
bandwidth (either noise or signal width).
- Kirt Blattenberger