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Spectrum Analyzer Measurement-How to set the RBW&VBW - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues - primarily having to spend time purging garbage posts from the board. At some point I might start the RF Cafe Forums again if the phpBB software gets better at filtering spam. Note: The RF Cafe Forums were reconstituted in April 2021!

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Simon Liu
 Post subject: Spectrum Analyzer Measurement-How to set the RBW&VBW
Posted: Wed Jan 19, 2005 1:33 am 
 
Captain
User avatar

Joined: Wed Jan 05, 2005 2:20 am
Posts: 9
Location: BeiJing,China
Hi , I am a new RF engineer.

As we known, when testing the isolation or Xth harmonic by spectrum analyzer,we need to set the poper RBW and VBW.Also they will effect on the sweep time.My question is do we have a standard to sepcify how to set the RBW&VBW since different RBW will result in different test result. Is there anyone could provide the App note for me?
:idea: :?: :!: ;-)

Thanks


 
   
 
Kirt Blattenberger
 Post subject:
Posted: Wed Jan 19, 2005 11:44 pm 
 
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Joined: Sun Aug 03, 2003 2:02 pm
Posts: 451
Location: Erie, PA
Greetings Simon:

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).

(1) https://www.rfcafe.com/references/test-notes.htm

- Kirt Blattenberger :smt024


 
   
 
Simon Liu
 Post subject:
Posted: Thu Jan 20, 2005 9:44 pm 
 
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Joined: Wed Jan 05, 2005 2:20 am
Posts: 9
Location: BeiJing,China
Got it.
Thanks man!
Simon


 
   
 
Guest
 Post subject:
Posted: Wed Feb 09, 2005 5:15 pm 
You'll also want to pay attention to the input power.
Most HP SA's are NF limited below -21dBm and IM limited above -21dBm.

That probably the most common mistake (incorrect attenuation) I have seen with users new to the spectrum analzer.




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