spectrum analyzer ( VBW & RBW )

why in spectrum analyzer bandwidth settings it is preferable the relation between Resolution Bandwidth (RBW) & Video Bandwidth (VBW) to be 1/3 ? means if the RBW is 30 KHz , it is preferable to have VBW with 10 KHz .

and if VBW filter is a Low passfilter , why lowering the value will slow down the speed of sweeping ?

i think ration could be 3/1 instead 1/3 pls check. it is preferred to have 1/1 so that there is no discrepancy between processing and video.
when the filter is low pass it needs more time to filtering due to order of the filter.
hope this helps you

Hi,

can you plz elaborate more on

when rbw reduces,means q is increasing. high q filter realization is possible with higher order which in turn needs more delay

thanks kspalla

could you please post some links explain what have you said in details with examples ?

thanks in advance

The speed of sweeping must be proportional to the resolution BW because a high-Q bandpass needs more time to settle than a low-Q bandpass. Only after the transient has been settled the bandpass can correctly operate as a search filter.

Do you mean LvM changing RBW willn't affect the sweeping time ?

For my feeling, I just have said the opposite: A smaller RBW requires lowering the sweep rate (otherwise "not calibrated").

Agilent application note: 8 Hints for better spectrum analysis.

sorry , i meant to say "Do you mean LvM changing VBW ( video Bandwidth ) willn't affect the sweeping time ?

as you have talked about the resolution BW only .

No, I didn't mention the VBW at all.

So what do you think in this regard ?