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Why is There a Peak at 0 Hz on Spectrum Analyzer - RF Cafe Forums

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Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement

 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 
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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.

Posted  11/12/2012

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