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

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Yariv3G

Post subject: Why is there a peak at 0 Hz on Spectrum Analyzer

Posted: Mon Dec 18, 2006 11:11 am

Captain

Joined: Mon Apr 03, 2006 4:06 am
Posts: 8

Hi,
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.
Yariv3G

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R&S RF Application Engineer

RFTEJerry

Post subject:

Posted: Thu Dec 28, 2006 12:46 pm

Captain

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,
RFTEJerry

sm7ovk

Post subject:

Posted: Sun Jan 14, 2007 3:11 pm

Captain

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?

Regards
Jens

CyberOli

Post subject:

Posted: Fri Jan 19, 2007 7:55 am

Captain

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.

Posted 11/12/2012

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