Re: [Discuss-gnuradio] Weird noise using RFX2400

[You Lizhao]

Hi Josh,

Thanks for your kind reply. The figure is shown in 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 Blum <address@hidden>

On 09/18/2012 09:27 AM, You Lizhao wrote:
> 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 .
>
> 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!

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/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

>
>
> Regards,
> Lizhao
>
>
>
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rfx2400_sample.png
Description: PNG image