Weird noise using RFX2400

GNU Radio
1

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!

Regards,
Lizhao

2

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
    c++ « examples « gr-uhd - gnuradio.git - GNU Radio

  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

3

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 B. [email protected]