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
sema
November 1, 2013, 5:05pm
2
Hi Sema,
You are most likely seeing the local oscillator at the centre due to the
WBX being a direct conversion daughterboard:
A direct-conversion receiver (DCR), also known as homodyne, synchrodyne, or zero-IF receiver, is a radio receiver design that demodulates the incoming radio signal using synchronous detection driven by a local oscillator whose frequency is identical to, or very close to the carrier frequency of the intended signal. This is in contrast to the standard superheterodyne receiver where this is accomplished only after an initial conversion to an intermediate frequency.
The simplification of performin...
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
November 5, 2013, 8:34pm
3
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