# Multitone IMD - RF Cafe Forums

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

ljoseph
Post subject: Multitone IMD Posted: Fri Oct 02, 2009 3:58 pm

Captain

Joined: Tue Sep 04, 2007 7:54 am
Posts: 13
Location: Dallas
Hi,

This is about IM calculations in case of multitone.

For example take an amplifier with OPI3 of 18.1dBm, gain =11 dB. Two tone IM is 58.2 dBc. Input is -19 dBm
Output = -19+11 = -8 dBm. IM = 2(18.1-(-8))+6 = 58.2dBc

Now, I am driving this amplifier with 15 tones each having an input power of -19-10*log(15)=-30.8dBm
Total output power for 15 input tones = -8 dBm.
What will be the worst case IM in dBC with respect to -8dBm of total output power?

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Kirt Blattenberger
Post subject: Re: Multitone IMDPosted: Fri Oct 09, 2009 3:32 pm

Joined: Sun Aug 03, 2003 2:02 pm
Posts: 308
Location: Erie, PA
Greetings ljoseph:

The link I used to have for a paper titled "A General Algorithm to Calculate Third Order Intermodulation Product Locations for any Number of Tones," by Chris Arnott, has disappeared from it's location on the CED website. So, I just scanned in and OCRed a copy provided to me by Chris back when I worked with him at RF Micro Devices. You can access it here:

http://www.rfcafe.com/references/electrical/calculate-imd-any-number-tones.htm

Hopefully that will get you where you're going.

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