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.
>
> Hmm, I tried to use this to change the LO offset:
> self.signal_source_0.set_center_freq(uhd.tune_request(self.freq+self.freq_offset,self.lo_off))
>
> However, now I have a new peak and this peak doesn't disappear when I turn
> off the transmitter.
>
> I am using a USRP2 and XCVR2450
>
> --
> Principal Investigator
> Shirleys Bay Radio Astronomy Consortium
> http://www.sbrac.org
>
>
>
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>
>
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