Re: [Discuss-gnuradio] Carrier leakage on transmit

[Johnathan Corgan]

On Tue, May 25, 2010 at 03:17, Charles Brain <address@hidden> wrote:

> Is there any way of calibrating out or mitigating the carrier at the WBX tx
> frequency? I am sending
> a wideband signal and the carrier (which I assume is due to dc coupling in
> the WBX) is at a significant level compared to my signal.

This is a result of feedthrough of the LO in the WBX mixer.

There is a function call you can make in the libusrp2 driver,
'set_lo_offset', which will adjust the analog LO in frequency and
compensate using the FPGA DUC to return the actual transmitted signal
to your desired tuned frequency.  I'm not sure what the equivalent
function in the UHD is; it may not be implemented yet.

This at least lets you move the spurious carrier outside the passband
of your transmit signal. In order to fully remove it, either DC offset
trimming would need to be implemented in the FPGA, or host
code/firmware written to tweak the built-in DAC DC offset
compensation.  I've done the former for clients, and it works well.

Johnathan