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4Tone*25W IMD3 Testing for Circulator? - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

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


gangsway
 Post subject: 4tone*25W IMD3 testing for circulator?
Posted: Sat Jun 27, 2009 10:24 am 
 
Captain

Joined: Tue Nov 11, 2008 5:03 am
Posts: 16
Location: Shanghai, China
I have a new design project for a circulator,which request 4tone *25W IMD3. I can not understand it, need your help regarding how to understnd, how to set-up the testing bench, what's the testing solution or idea? Appreciate!

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bhawkins
 Post subject: Re: 4tone*25W IMD3 testing for circulator?
Posted: Wed Jul 22, 2009 4:26 pm 
 
Captain

Joined: Sun Feb 15, 2009 9:54 pm
Posts: 9
i doubt if there's any off the shelf solution, like there is for 2-tones.

i'd guess you would use 3 2-way combiners; 3 low im circulators; several low im bpf's; a spectrum analyzer all these components have to have better im performance than what you're designing

i'm curious; why 4-tones? what frequency? how low an im do you need?


bob hawkins
www.fairviewmicrowave.com


 
   
 
nubbage
 Post subject: Re: 4tone*25W IMD3 testing for circulator?
Posted: Fri Jul 24, 2009 3:25 am 
 
General
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 268
Location: London UK
Hi gangsway
Bob is right: we need more info.
Just to give an example: If you have a situation with 4 unmodulated carriers on fairly widely different frequencies, such as across the UHF PMR radio band, it is fairly straight forward to predict the third order and 5th order IM frequencies that result when all 4 pass through a non-linear system.
The fiendishly difficult thing is to predict accurately what the relative levels will be.
Pragmatically, I approached this once by predicting the frequencies of the products using simple software, and then used a Tuneable Band Pass Filter to pick off each one. I then measured each level with a calibrated high dynamic range receiver, calibrated against an Agilent signal generator. It was more laborious than using a Spectrum Analyzer, but frankly the analyzer is more likely to generate as much IMPs as the process you are studying.
Give us more data to work with.

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gangsway
 Post subject: Re: 4tone*25W IMD3 testing for circulator?
Posted: Tue Aug 11, 2009 10:34 pm 
 
Captain

Joined: Tue Nov 11, 2008 5:03 am
Posts: 16
Location: Shanghai, China
Thanks very much.
I used four 8648C, plus 3 combiners, NF and 8561E Spectrum analyzer to have the testing done.

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