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

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

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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 
 
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

_________________
R&S RF Application Engineer


 
   
 
 Post subject:
Posted: Thu Dec 28, 2006 12:46 pm 
 
Captain
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,
RFTEJerry


 
   
 
 Post subject:
Posted: Sun Jan 14, 2007 3:11 pm 
 
Captain
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?

Regards
Jens


 
   
 
 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.





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