The Designer's Guide Community
Forum
Welcome, Guest. Please Login or Register. Please follow the Forum guidelines.
Jun 19th, 2019, 10:34pm
Pages: 1
Send Topic Print
Spectrum analyzer (Read 6688 times)
raja.cedt
Senior Fellow
******
Offline



Posts: 1516
Germany
Spectrum analyzer
Aug 19th, 2010, 5:23am
 
hello,
can any one please tell me what is RBW and VBW in spectrum analyzer? Everybody is telling that lesser the RBW more accuracy in the measurement. can any one clarify this or direct me towards a ref..

Thanks,
Rajasekhar.
Back to top
 
 
View Profile WWW raja.sekhar86   IP Logged
aaron_do
Senior Fellow
******
Offline



Posts: 1398

Re: Spectrum analyzer
Reply #1 - Aug 19th, 2010, 6:28am
 
Hi,


I suggest you google some documents on spectrum analyzer fundamentals. The documents by Agilent are very helpful.

A spectrum analyzer is similar to an AM receiver. Anyway RBW is the resolution bandwidth and if you are familiar with receiver design (which is basically what a spectrum analzyer is), it is your channel filter bandwidth. i.e. it is the filter after the frequency translation. A narrower RBW will lower the noise floor potentially making your signal more clear. After the RBW filter, the signal is basically amplitude detected using some kind of rectifier. And following this rectifier is another filter which is basically your VBW filter. Reducing the VBW is akin to averaging the signal power. It does not reduce the average level of the signal or noise, but it removes all the large spikes you see in the noise also potentially making your signal clearer. So to sum up, reducing RBW lowers the noise floor, while reducing the VBW smooths out the noise.

Modern high-end spectrum analyzers are implemented quite differently. Basically they can digitize the signal much sooner, but the basic principles of RBW and VBW are the same.

Anyway like I said you're much better off reading some of those Agilent documents on spectrum analyzer fundamentals.


cheers,
Aaron
Back to top
 
 

there is no energy in matter other than that received from the environment - Nikola Tesla
View Profile   IP Logged
raja.cedt
Senior Fellow
******
Offline



Posts: 1516
Germany
Re: Spectrum analyzer
Reply #2 - Aug 19th, 2010, 10:39pm
 
hi
tx for your reply...i have gone through some documents, so finally what i have understood is if RBW=1hz then we will get correct noise..is this correct?

Thanks,
Rajasekhar.
Back to top
 
 
View Profile WWW raja.sekhar86   IP Logged
pancho_hideboo
Senior Fellow
******
Offline



Posts: 1424
Real Homeless
Re: Spectrum analyzer
Reply #3 - Aug 20th, 2010, 8:28am
 
raja.cedt wrote on Aug 19th, 2010, 10:39pm:
so finally what i have understood is if RBW=1hz then we will get correct noise..is this correct?
Not correct.

Noise marker mode in Spectrum Analyzer where dBm/Hz or dBc/Hz is displayed has no relation to RBW directly.
Back to top
 
 
View Profile WWW Top+Secret Top+Secret   IP Logged
RFICDUDE
Community Fellow
*****
Offline



Posts: 323

Re: Spectrum analyzer
Reply #4 - Aug 22nd, 2010, 6:05pm
 
Back to top
 
 
View Profile   IP Logged
Pages: 1
Send Topic Print
Copyright 2002-2019 Designer’s Guide Consulting, Inc. Designer’s Guide® is a registered trademark of Designer’s Guide Consulting, Inc. All rights reserved. Send comments or questions to editor@designers-guide.org. Consider submitting a paper or model.