# Weird noise using RFX2400

**URL:** <https://www.ruby-forum.com/t/weird-noise-using-rfx2400/223000>\
**Category:** GNU Radio\
**Created:** [September 18, 2012, 3:29pm UTC](https://www.ruby-forum.com/t/weird-noise-using-rfx2400/223000 "2012-09-18T15:29:14Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![aris](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/258eb7/32.png) [@aris](https://www.ruby-forum.com/u/aris)\
**Post date:** [September 18, 2012, 3:29pm UTC](https://www.ruby-forum.com/t/weird-noise-using-rfx2400/223000/1 "2012-09-18T15:29:14Z")

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Hi All,

I have used RFX2400+N210 to sample real-time OFDM signal, and found that  
there are two suspicious noises, which are shown in attachment or  
[http://uploadpie.com/vcX3j](http://uploadpie.com/vcX3j) .

One suspicious noise appears at the start-up stage of N210, and the  
other  
suspicious noise appears at the end of a packet. The unwanted noise may  
ruin my ofdm\_sync algorithm. So I am wondering that is it possible to  
get  
rid of these noises? How do they come?

BTW, I use GNURadio v3.6.3 and UHD driver cloned at Sep. 11. Any  
comments  
are appreciated. Thanks!

Regards,  
Lizhao

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**Author:** ![You\_L](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/9fc29f/32.png) [@You\_L](https://www.ruby-forum.com/u/You_L)\
**Post date:** [September 18, 2012, 7:36pm UTC](https://www.ruby-forum.com/t/weird-noise-using-rfx2400/223000/2 "2012-09-18T19:36:30Z")

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On 09/18/2012 09:27 AM, You L. wrote:

> BTW, I use GNURadio v3.6.3 and UHD driver cloned at Sep. 11. Any comments  
> are appreciated. Thanks!

I couldnt see the upload pie link. Perhaps you are seeing transients  
when TX stops. I guess I have 2 suggestions:

1. make sure you are ending the transmit burst with the EOB tag  
[http://gnuradio.org/cgit/gnuradio.git/tree/gr-uhd/include/gr\_uhd\_usrp\_sink.h#n59](http://gnuradio.org/cgit/gnuradio.git/tree/gr-uhd/include/gr_uhd_usrp_sink.h#n59)  
[c++ « examples « gr-uhd - gnuradio.git - GNU Radio](http://gnuradio.org/cgit/gnuradio.git/tree/gr-uhd/examples/c++)

2. Also its good to pad out the burst/ofdm frame to push the frame  
through the TX DSP filters, and also to mitigate transients.

-josh

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<div class="post-metadata">

**Author:** ![You\_L](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/9fc29f/32.png) [@You\_L](https://www.ruby-forum.com/u/You_L)\
**Post date:** [September 19, 2012, 9:44am UTC](https://www.ruby-forum.com/t/weird-noise-using-rfx2400/223000/3 "2012-09-19T09:44:19Z")

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Hi Josh,

Thanks for your kind reply. The figure is shown in  
[http://dl.dropbox.com/u/39710586/rfx2400\_sample.png](http://dl.dropbox.com/u/39710586/rfx2400_sample.png) .

I guess it is not caused by Tx transient, because:

1. The TX N210 is just dedicated to TX path in my application, and thus  
does not have Tx/Rx switch capability;
2. I have used XCVR2450 to receive sampled data (uhd\_rx\_cfile.py) with  
the  
same tx setup (Tx uses RFX2400), but there is no such high noise.

Maybe I should switch to the usrp-user mail-list?

Regards,  
Lizhao

2012/9/19 Josh B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)