using spectrum analyzer to measure WLAN signal

I am trying to use a spectrum analyzer to measure WLAN OFDM signal.
However, I can only see slices of the 20MHz OFDM signal instead of the
whole 20MHz span. Do I need a special setting (RBW, sweep time) in
order to see the whole 20MHz span?

Thanks.

 

[Steve]

<feilip@gmail.com> wrote in message
news:971a2aed-4d59-456d-a9ef-2a801ddbdb06@h11g2000prf.googlegroups.com...

I am trying to use a spectrum analyzer to measure WLAN OFDM signal.
However, I can only see slices of the 20MHz OFDM signal instead of the
whole 20MHz span. Do I need a special setting (RBW, sweep time) in
order to see the whole 20MHz span?

Thanks.

The analyzer's sweep time is not matched to the OFDM changes, so you only
see those portions where the signal happens to coincide (in time) with the
SA's own instantaneous tuned frequency . Sweep with Max Hold will build up
the peak envelope over many sweeps. But you won't be able to discern much
detail about the modulation that way. And noise spikes will be "remembered"
along with signal, so the amplitude may appear higher than it actually is.

Are you using an amplifier ahead of the SA, to reduce its effective noise
figure and increase your dynamic range?

Steve