[USRP-users] spectral leakage ?!

mleech at ripnet.com mleech at ripnet.com
Fri Oct 2 10:24:07 EDT 2015


 

You can use offset tuning to move the DC anomaly out-of-band. Both in
the TX and RX direction: 

http://files.ettus.com/manual/page_general.html 

All superhet TX/RX have some amount of LO leakage. With
direct-conversion (Zero IF), that leakage happens to be in-band. So, you
can make this more like a non-zero-IF design using offset tuning. There
will still be leakage, but it will be out-of-band. 

On 2015-10-02 09:55, James Humphries via USRP-users wrote: 

> Some LO leakage is typical with the system. When you say sometimes not necessarily at the center frequency, how far away from center is it? 
> 
> -Trip 
> 
> On Thu, Oct 1, 2015 at 7:53 AM, Amina M. Fellan via USRP-users <usrp-users at lists.ettus.com> wrote:
> 
>> Hello everybody ! 
>> 
>> I'm using 2 USRPs N210 equipped with SBX daughterboards with GNU Radio to establish BPSK communication over ISM band. For the latter, I started with the benchmark_tx/_rx.py examples. 
>> 
>> currently I'm trying to measure the SNR at the receiver. I tried using the SNR estimation blocks in the GRC but they seem to be giving erroneous readings, so I decided to try with a spectrum analyzer to estimate the SNR using (S+N)/N. 
>> 
>> I noticed that even when there's no transmission going on, so trying to measure the noise floor, a signal appears on the spectrum and sometimes even not necessarily at the center frequency. This also can be seen using the uhd_fft script from GNU Radio. Attached is a photo of how the spectrum looks if the USRP is on without transmitting/receiving !! 
>> 
>> Any clues what is causing this problem ?? 
>> 
>> Thanks for your time ! 
>> 
>> Cheers,
>> Amina 
>> 
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> 
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