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BPSK strange peaks with 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.

Below are all of the forum threads, including all the responses to the original posts.


 Post subject: BPSK strange peaks with spectrum analyzer
Posted: Wed Mar 25, 2009 3:40 pm 
 
Lieutenant

Joined: Wed Mar 25, 2009 3:33 pm
Posts: 1
Maybe someone can help me:

I used spectrum analyzer with very big rbw to view bpsk signal in peak mode(not RMS).
the data was random

I saw the familiar sinc envalope with nulls at N*Rb (N-integer) .
what's strange is that also I saw strange peaks at LO and multiples of Rb/2.
If I lower the RBW or put detector in RMS the peaks disappear.

I verified it with 2 different signal generators.

It's wither a charectaristic of the signal or spectrum analyzer related phoneomena.

PLEASE HELP ME

confused from Israel....


 
   
 
 Post subject: Re: BPSK strange peaks with spectrum analyzer
Posted: Sat Apr 11, 2009 11:42 am 
 
Captain
User avatar

Joined: Thu May 04, 2006 7:37 am
Posts: 8
Lurker:

Sounds like LO leakage from improper DC cancellation. You might want to check your DC levels on I/Q data input to the modulator.


 
   
 
 Post subject: Re: BPSK strange peaks with spectrum analyzer
Posted: Sat Apr 11, 2009 8:14 pm 
 
Captain
User avatar

Joined: Wed Apr 08, 2009 7:53 am
Posts: 17
Hello Lurker,

It is normal to have different measurement results if you read power to a digital modulated signal with different RBW.
Perhaps the best way to analyze peaks on a signal is to trace CCDF curves.
Check if you still have those peaks near LO when filtering a CW or without any signal.. If the tones disappear, then perhaps you have some DC filtering problem.. if they still there, then is something on the synthesizer design..

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