# Cross-correlating Two FFT signals

**URL:** <https://www.ruby-forum.com/t/cross-correlating-two-fft-signals/231123>\
**Category:** GNU Radio\
**Created:** [July 22, 2014, 4:04pm UTC](https://www.ruby-forum.com/t/cross-correlating-two-fft-signals/231123 "2014-07-22T16:04:18Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [July 22, 2014, 4:04pm UTC](https://www.ruby-forum.com/t/cross-correlating-two-fft-signals/231123/1 "2014-07-22T16:04:18Z")

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Hello,

I’m trying to find a way that I could cross-correlate two FFT signals  
that I have coming in from two UDP networks, anyone know of a block I  
can do that with?

Thanks in advance,  
Marcus

---

<div class="post-metadata">

**Author:** ![WardS\_Marcus\_D](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/ccd318/32.png) [@WardS\_Marcus\_D](https://www.ruby-forum.com/u/WardS_Marcus_D)\
**Post date:** [July 22, 2014, 6:22pm UTC](https://www.ruby-forum.com/t/cross-correlating-two-fft-signals/231123/2 "2014-07-22T18:22:18Z")

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On 07/22/2014 04:02 PM, Ward, Marcus D. wrote:

> Hello,
> 
> I’m trying to find a way that I could cross-correlate two FFT signals  
> that I have coming in from two UDP networks, anyone know of a block I  
> can do that with?

There’s no dedicated xcorr-block, but you can do a fast correlation  
using FFTs and point-wise multiplication.

M

---

<div class="post-metadata">

**Author:** ![WardS\_Marcus\_D](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/ccd318/32.png) [@WardS\_Marcus\_D](https://www.ruby-forum.com/u/WardS_Marcus_D)\
**Post date:** [July 22, 2014, 7:34pm UTC](https://www.ruby-forum.com/t/cross-correlating-two-fft-signals/231123/3 "2014-07-22T19:34:02Z")

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Thanks Martin, I’ll try that and also I don’t happen to see any Inverse  
FFT blocks on Gnu-radio, is there a way I can do the IFFT on GNU-radio  
since there is no block for it?

---

<div class="post-metadata">

**Author:** ![WardS\_Marcus\_D](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/ccd318/32.png) [@WardS\_Marcus\_D](https://www.ruby-forum.com/u/WardS_Marcus_D)\
**Post date:** [July 22, 2014, 7:38pm UTC](https://www.ruby-forum.com/t/cross-correlating-two-fft-signals/231123/4 "2014-07-22T19:38:22Z")

</div>

On 07/22/2014 01:32 PM, Ward, Marcus D. wrote:

> Thanks Martin, I’ll try that and also I don’t happen to see any Inverse FFT  
> blocks on Gnu-radio, is there a way I can do the IFFT on GNU-radio since there is  
> no block for it?  
> The FFT block has a parameter that says “Forward” or “Reverse” (or  
> Inverse).

> > that I have coming in from two UDP networks, anyone know of a block I
> 
> * * *
> 
> Discuss-gnuradio mailing list  
> [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
> [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio)
> 
> * * *
> 
> Discuss-gnuradio mailing list  
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> [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio)

–  
Marcus L.  
Principal Investigator  
Shirleys Bay Radio Astronomy Consortium

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