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# Amplifier 3-rd order inter-modulation product - RF Cafe Forums

 The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Below are all of the old forum threads, including all the responses to the original posts. -- Amateur Radio -- Antennas-- CAE, CAD, & Software-- Circuits & Components-- Systems-- Test & Measurement

 Post subject: Amplifier 3-rd order inter-modulation product Posted: Fri Oct 29, 2010 3:58 pm
 Lieutenant

Joined: Wed Mar 31, 2010 2:46 am
Posts: 3
 Hello,I have some problem in prediction of 3-rd order inter-modulation product level . Usually, IMP3 is defined analytically for the case that both tones are of the same level and frequency difference between them is less than 5% of their frequency (in-band conditions).I have a different case: f1 tone is of 49 dBm at 430 MHz, and f2 tone is of 29 dBm at 549 MHz. So, they have different levels and are spread wide.I am interested to predict the level of lower IMP3 (2*f1-f2) at 311 MHz.I am looking for analytical equation and physical/mathematical explanation, which will take in account the wide distance between tones at frequency axes and also their difference in power levels. Any theoretical explanation and/or links will be appretiated.I look also for translation between measurement results taken by classical approach and my special case.For example, I have to understand whether results of classical measurement of OIP3 may be applied somehow to my special case and reliably predict "my" IMP3 at 311 MHz.ThanksPavel

Posted  11/12/2012