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4tone*25W IMD3 testing for circulator? - RF Cafe Forums

RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2010, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. Regardless, there are still lots of great posts in the archive that ware worth looking at. Below are the old forum threads, including responses to the original posts.

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

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!


glad to learn from you

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

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


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


At bottom, life is all about

Sucking in and blowing out.

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

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.


glad to learn from you

Posted  11/12/2012

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