discuss-gnuradio
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Discuss-gnuradio] USRP inserts a peak in the carrier frequency


From: frankist
Subject: Re: [Discuss-gnuradio] USRP inserts a peak in the carrier frequency
Date: Sun, 15 Apr 2012 06:27:45 -0700 (PDT)

Now I have another problem related to peaks in the fft plot, but in this
case, with no transmitter.

Why does a peak appears at the center of the fft plot for some frequencies
and not for the others. I mean, I am using a USRP2 to receive just noise and
plot its fft and when I center my receiver in the frequencies 5.0GHz, 5.5
GHz and 6.0 GHz I have no peaks but for the other frequencies in the same
band I do have them.

In this case it is not related to LO leakage since I can't get rid of them
and I have no transmitter. Also, the peak always appears at the center of
the plot


frankist wrote:
> 
> Oops. problem solved. I had to increase the LO offset in the transmitter
> (not the receiver)! *Facepalm*
> 
> Thanks for the support
> 
> 
> mleech wrote:
>> 
>> On 07/04/12 10:12 AM, frankist wrote:
>>> Hi,
>>>
>>> I am using GNU Radio for 2 weeks. I always get in the receiver side a
>>> signal
>>> with a peak in the carrier frequency when I turn on the transmitter even
>>> if
>>> I send a signal made of zeros. You can see it in the picture 
>>> http://old.nabble.com/file/p33648622/usrp_carrier_peak.png 
>>>
>>> In spite of being handy to discover the frequency offset of my signal,
>>> it is
>>> influencing my results when I try to measure the power of the received
>>> signal. I thought this was the DC offset, but I read somewhere that
>>> USRP2
>>> eliminates the DC Offset.
>>>
>>> So, do you know what it is and how to remove it?
>>>   
>> This is LO leakage. What is you setup here--two USRPs with XCVR cards?
>> 
>> Mixers always have some amount of LO leakage at the output port. 
>> Depending on your signal bandwidth,
>>  you can use an LO offset to move that leakage outside of your
>> applications passband, but there'll still be
>>  leakage--just not at a place that matters to you.
>> 
>> -- 
>> Principal Investigator
>> Shirleys Bay Radio Astronomy Consortium
>> http://www.sbrac.org
>> 
>> 
>> 
>> _______________________________________________
>> Discuss-gnuradio mailing list
>> address@hidden
>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>> 
>> 
> 
> 

-- 
View this message in context: 
http://old.nabble.com/USRP-inserts-a-peak-in-the-carrier-frequency-tp33648622p33688986.html
Sent from the GnuRadio mailing list archive at Nabble.com.




reply via email to

[Prev in Thread] Current Thread [Next in Thread]