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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
>>
>>
>
>
--
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