[USRP-users] Removing the whole LO signal when transmitting

Brais Ares bares at gradiant.org
Fri Jul 14 11:42:51 EDT 2017


Hello everyone

I'm trying to implement a *rx-tx RF* *loopback *but I may be having
problems with local oscillators.

The signal to capture is 100 KHz, so I configure rx-bw and tx-bw to its
minimum values (286 KHz and 782 KHz), and Fs to 286 KSPS.

As far as I understood reading this thread
<https://dsp.stackexchange.com/questions/30562/large-spike-at-the-center-frequency-when-using-ettus-x310>,
I can avoid capturing the LO in RX by adding an *lo_off value to
"tune_request"*, this value being larger than Bsample/2. So I configure the
following lo_off:

RX (bw=286 KHz), lo_off = 200e3
TX (bw=782 KHz), lo_off = 500e3

​If I capture the transmitted signal with a spectrum analyzer I can see my
​signal centered where expected, but also, out-of-band I can find the LO
signal with high power and a replica.

[image: Imágenes integradas 4]

Is this the expected behaviour or is there any way to actually remove them?

​Regards,
Brais.​

​​
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