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Clarification:

Started by abathla August 1, 2007
Sorry for the confusion.
I want to find magnitude of I and Q at the same frequency and I need to
compare the two values for my purpose. Similarly, I need to find phase of
I and Q at that same ferquency and compare them. Is goertzel the fastest
way to do it?

Also, i couldnt understand what the two states of the filter are, as said
by Tim.

Thanks
AB
abathla wrote:
> Sorry for the confusion. > I want to find magnitude of I and Q at the same frequency and I need to > compare the two values for my purpose. Similarly, I need to find phase of > I and Q at that same ferquency and compare them. Is goertzel the fastest > way to do it? > > Also, i couldnt understand what the two states of the filter are, as said > by Tim. > > Thanks > AB
Netiquette: Please respond within the thread. Starting a new thread defeats the purpose of newsreaders that track things by threads. About your question: Maybe. You would probably be better off multiplying your I and Q signals by sin(2*pi*f*t) and cos(2*pi*f*t) and integrating the results over one cycle (note that you'll have _four_ answers to juggle). I'm trying to wrap my head around the math, wondering if the relative phase of I and Q isn't always going to be 90 degrees, but it won't go there this morning. Any 2nd-order filter has to carry two states. In the implementations of Goertzel that I've seen these are the current output and the previous tick's output. If you do a full-cycle Goertzel then the previous tick's output will be zero and the current one will be the 'answer'. If you don't do a full cycle you have to scale the previous output and add it to the current one to get the 'right' answer. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html