Setting the DSP frequency in the UHD blocks

GNU Radio
1

In gnu radio companion for a UHD block, how do I set the DSP frequency
as well as the RF frequency. I have done this in my C code which
doesn’t use gnuradio using the tune_request_t structure. From the
comments in the python code, it appears that there is some way to do it.

I understand that I want to use the DSP LO so that the DC component from
the ADC is moved outside the baseband. Is there a good value or is
anything outside my receive bandwidth is ok?

Is there a reason to use the DSP LO on the transmit side? Does the up
conversion happen before or after the DSP LO?

Thanks,
Frank Wallace

2

Discuss-gnuradio mailing list
[email protected]
Discuss-gnuradio Info Page
There’s a uhd “helper function” that gets imported to allow you to do
this:

Where the UHD block takes frequency, you can replace it with:

uhd.tune_request (target_freq, lo_ffset)

The RF upconversion happens after the DSP on the TX side. It may be
beneficial to move the LO on the TX side as well.

3

Hi Frank,

Use the following line as the frequency variable for the ‘UHD Source’ &
‘UHD Sink’ blocks in GRC:

uhd.tune_request(center_freq,
rf_freq=(center_freq+lo_offset),rf_freq_policy=uhd.tune_request.POLICY_MANUAL)

Where ‘center_freq’ and ‘lo_freq’ are variables which need to be
defined.

Using the lo_offset on the TX side prevents local oscilator leakage on
the
TX frequency, to prevent giving the false impression that it is
transmitting after stopping the flowgraph.

Regards,

Mike

–
Mike J. M0MIK BSc MIET
Email: [email protected]
Web: http://scanoo.com

On Mon, Jul 1, 2013 at 6:38 PM, Wallace, Frank L CIV NSWCDD, Q41 <