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IQ demodulation help - 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.


antennaant
Post subject: IQ demodulation help Posted: Sat Sep 12, 2009 4:16 am

Lieutenant

Joined: Mon Dec 11, 2006 3:17 pm
Posts: 2
This suddenly came up in a MRI class. I kinda understand IQ modulation (both amplitude and phase are modulated). But how does IQ demodulating a signal help, specially MRI signal.
In case you don't know a MRI signal, its just a exponentially decaying sine.
Also, what is instantaneous phase ?


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Jose Arrina
Post subject: Re: IQ demodulation helpPosted: Wed Sep 16, 2009 12:25 pm

Lieutenant


Joined: Thu Mar 30, 2006 9:01 am
Posts: 4
Hi antennaant:

I'm fairly new at quadrature systems, but basically breaking down a signal into I and Q components allows you to discern angle of arrival, or phase. If you have two detectors orthogonal to each other (90 deg), then mathematically they are independent. So, assuming both antennas are subject to the same signal, the amplitudes of each relative to the other indicates phase. It's a sin vs. cos calculation. This scheme is used in threat detector systems for determining angle of arrival.

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