[SI-LIST] Re: The function of VBW in spectrum analyzer
- From: "Ray Anderson" <ray.anderson@xxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Fri, 13 May 2005 07:34:45 -0700
Zhangkun-
Spectrum analyzers usually provide both VBW (video bandwidth) control
and smoothing or averaging functions.
VBW control is typically accomplished by passing the signal through a
low pass filter to restrict the bandwidth of the displayed signal. This
eliminates a lot of high-frequency noise. Older analyzers utilized an
analog video filter whereas most modern instruments probably use digital
filters.
Averaging or smoothing is a moving average type function as Istvan has
described. It too performs low pass filtering but in a different manner.
Most modern analyzers coupled the sweep rate to the analyzers bandwidth
such that there isn't too much degradation in amplitude accuracy caused
by the filtering functions. This coupling can be overridden. If this is
done it is up to the user to ensure the analyzer isn't swept too fast
for the bandwidth selected.
Zhankun, you mention spectrum analyzer in the beginning of your inquiry
and then shift to a discussion of s-parameters at the end, so I'm not
sure if your question was VNA or SA related, however most of the
comments do apply to both instruments.
-Ray
Raymond Anderson
Senior Signal Integrity Staff Engineer
Product Technology Department
Advanced Package R&D
Xilinx Inc.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Istvan Novak
Sent: Friday, May 13, 2005 5:31 AM
To: zhang_kun@xxxxxxxxxx
Cc: si-list
Subject: [SI-LIST] Re: The function of VBW in spectrum analyzer
Dear Zhangkun,
Usually smoothing is done by applying a moving average of (2*N+1)=20
points: at each measurement point, you average the measured value with=20
the values of N points to the left and N points to the right. =20
Weightingh can also be applied, so to be absolutely sure, you may need=20
to check the manual and/or ask the manufacturer.
Regards,
Istvan
Zhangkun wrote:
>Dear all
>In the spectrum analyzer, there is a parameter, VBW, which could make
the curve more smooth. Now I have some measured s1p file. I want to make
it smooth. Could anybody tell me the equivalent circuit about VBW.
Therefore, I could apply it to my s1p files and make it smooth.
>
>Best Regards
>
>Zhangkun
>2005.5.13
>
>
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