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My received signal looks like an AM signal

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Hello,

 I just started experimenting with the USRP , I have two USRP N200 and I am trying to make them to communicate with each other. I generate a simple 8Khz sine wave on the usrp that plays the role of the transmitter and then I send the signal via cable to the receiving usrp. The problem is that the received signal looks like an AM signal with its amplitude changing all the time, however the spectrum analyzer that I have put in my VI shows that I am receiving an signal with 8KHz frequency just as the one i have sent, how can I fix this. I attached the screenshots and the VIs of my application.

Thanks 

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Message 1 of 6
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That is very odd. I know your VIs are very close to the example code, but does this behavior occur when using the example code?

 

The biggest difference I can see if that in your code you are only generating I data and not Q data. I would try the example niUSRP EX Tx Continuous Async.vi located at

 

C:\Program Files (x86)\National Instruments\LabVIEW 2016\examples\instr\niUSRP

 

Cheers,

Michael

Michael Bilyk
Former NI Software Engineer (IT)
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Actually this is the example I used to make my code, I just deleted the Q generating part. When I run the example as it is it worked like a charm. I will try some more examples to configure if the usrps work properly. Is there a possibility that the cable causes this problem?

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Solution
Accepted by topic author CrazyEce91

Hi CrazyEce91,

 

That problem is caused by the fact that you are not generating both I and Q data. The issue occurs during the mixing phase; I believe it occurs during up-conversion. I could be wrong, it could also be on the Rx side with down-conversion. But either way you should generate both I and Q data. Is there a particular reason you deleted the Q generating portion of the code?

 

Cheers,

Michael

Michael Bilyk
Former NI Software Engineer (IT)
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Yes it was because I didn't send any Q Data. When I sent Q data as well it worked just fine. I wanted to send just a sine wave but I hadn't realized that usrp handles only IQ Data. This thread also helped me a lot http://forums.ni.com/t5/USRP-Software-Radio/USRP-can-only-use-IQ-modulation-Why-if-I-only-use-I-data....

cheers

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Awesome! Mark your last post as the solution to help others in the future.

 

Cheers,

Michael

Michael Bilyk
Former NI Software Engineer (IT)
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