# Mixing two signals for Radar application

**URL:** <https://www.ruby-forum.com/t/mixing-two-signals-for-radar-application/240079>\
**Category:** GNU Radio\
**Created:** [March 26, 2014, 3:19pm UTC](https://www.ruby-forum.com/t/mixing-two-signals-for-radar-application/240079 "2014-03-26T15:19:53Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\
**Post date:** [March 26, 2014, 3:19pm UTC](https://www.ruby-forum.com/t/mixing-two-signals-for-radar-application/240079/1 "2014-03-26T15:19:53Z")

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Hi list,  
I am in the process of building an FMCW radar. For this  
to work, I have to mix two signals. I tried to do it with the  
“multiply” block but no luck. I tried then to see how exactly this  
block works. It seems that it does not behave As it should be. Referring  
to  
theory, I should see the sum and the difference of the two signals.  
Looking at  
the FFT plot, I can’t say that works.

What am I doing wrong? Am I missing something?

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**Author:** ![Dimitris\_Siafarikas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9fc29f/32.png) [@Dimitris\_Siafarikas](https://www.ruby-forum.com/u/Dimitris_Siafarikas)\
**Post date:** [March 26, 2014, 3:29pm UTC](https://www.ruby-forum.com/t/mixing-two-signals-for-radar-application/240079/2 "2014-03-26T15:29:50Z")

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Hi Dimitris,

in theory, mixing should be exactly what you’re doing - the  
multiplication of a signal with another one.

Without you posting what your flow graph looks like or what the signal  
you get out of it actually is, helping you might be a bit hard…  
Please supply as much information as necessary to understand what  
might be going wrong 😉

Greetings,  
Marcus

On 26.03.2014 15:18, Dimitris Siafarikas wrote:

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**Author:** ![Dimitris\_Siafarikas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9fc29f/32.png) [@Dimitris\_Siafarikas](https://www.ruby-forum.com/u/Dimitris_Siafarikas)\
**Post date:** [March 27, 2014, 9:57am UTC](https://www.ruby-forum.com/t/mixing-two-signals-for-radar-application/240079/3 "2014-03-27T09:57:14Z")

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On 03/26/2014 03:18 PM, Dimitris Siafarikas wrote:

> Hi list,
> 
> I am in the process of building an FMCW radar. For this to work, I have  
> to mix two signals. I tried to do it with the “multiply” block but no  
> luck. I tried then to see how exactly this block works. It seems that it  
> does not behave As it should be. Referring to theory, I should see the  
> sum and the difference of the two signals. Looking at the FFT plot, I  
> can’t say that works.

That’s true for real mixing. I assume you’re doing complex multiplying.

M