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

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