DC Nonexistent Peak at Transmitter

Hi all,

I am trying to create a complex cosine signal in 100kHz and transmit it
with USRP in 110MHz using WBX daughterboard. I have observed this signal
in an oscilloscope and a spectrum analyzer. It can be seen that there is
a nonexistent peak at transmit frequency of USRP. I also added the
related photos to be clear.

Any help would be kindly appreciated.

Sema

Hi Sema,

You are most likely seeing the local oscillator at the centre due to the
WBX being a direct conversion daughterboard:

http://en.wikipedia.org/wiki/Direct-conversion_receiver

To remove this, you can put the following in the center frequency box of
the UHD source/sink block in GRC:

uhd.tune_request(uhd_center_freq,
rf_freq=(uhd_center_freq+uhd_lo_offset),rf_freq_policy=uhd.tune_request.POLICY_MANUAL)

The ‘uhd_center_freq’ and ‘uhd_lo_offset’ need to be specified. Set
‘uhd_lo_offset’ to be something like ((samp_rate/2)*1.1).

Regards,

Mike


Mike J. M0MIK BSc MIET
Ettus R. Technical Support
Email: [email protected]
Web: http://www.ettus.com http://www.ettus.com

Sema -

Also, please be sure you run the calibrations provided by UHD. The TX DC
Offset calibration addresses exactly what you are talking about.

http://files.ettus.com/uhd_docs/manual/html/calibration.html

Cheers,
Ben

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