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Why is there a peak at 0 Hz on Spectrum Analyzer - RF Cafe Forums

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 Post subject: Why is there a peak at 0 Hz on Spectrum Analyzer
Posted: Mon Dec 18, 2006 11:11 am 

Joined: Mon Apr 03, 2006 4:06 am

Posts: 8


I am using a spectrum analyzer that has a measurement range from 9kHz up to GHz. When chosing a Start freq at 0Hz and span of 100 MHz, I see a peak from 0 Hz although I don't measure anything (Open).

Has this something to do with the VBW Filter?

I have seen this quite often but never have been asked about this...

Can someone give me a convincing explaination?

Thanks for any hint.



R&S RF Application Engineer

 Post subject:
Posted: Thu Dec 28, 2006 12:46 pm 
User avatar

Joined: Thu Apr 13, 2006 9:53 am

Posts: 17

Location: Florida

The response at 0 Hz is due to the Spec-Ana's LO feedthru. Read Aglient's application note AN150, Spectrum Analyzer Basics for the details.

Godd luck,


 Post subject:
Posted: Sun Jan 14, 2007 3:11 pm 
User avatar

Joined: Thu Jan 11, 2007 12:59 pm

Posts: 16

Long time ago since I was at school, but isn't the mathematical explanation that the fourier transform has "problems" with 0Hz?



 Post subject:
Posted: Fri Jan 19, 2007 7:55 am 

Joined: Thu Jan 18, 2007 8:09 am

Posts: 12

Location: Belgium

It's not really a "problem", but the Fourrier transform of a 0 Hz signal (direct signal) gives a Dirac Pulse at 0 Hz. If I remember well.

The agilent document given by RFTEJerry is very good to well understand the functioning of a spectrum analyzer.

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