Hi Pedro,
Interestingly, just found Marcus answered a similar question a few years back:
https://dsp.stackexchange.com/questions/30562/large-spike-at-the-center-frequency-when-using-ettus-x310
Your calibration range is pretty small. I normally calibrate from 500M - 6G
such that it can support multiple applications. It will take some time, but
calibrating 1G should be quick.
USRP may not be able to generate LO exactly at 3.5GHz. In such case, it will
try to generate LO as close as possible.
Which UHD version are you using?
What are the master clock rate and sampling rate?
If calibration doesn't have any effect on your received signal, the USRP device
may be faulty, or the analyzer is problematic. A few things you can try:1. send
0s and you may see just a spike at the centre without signal;2. allocate your
modulation symbols to one side, lower or upper, of the OFDM resource grid, the
signal spectrum will go to one side and should not be impacted by the central
spike;3. Use USRP as receiver. Loop back Tx to Rx of the same USRP. Plot the
spectrum of the received signal to see if there is central spike.
Kind regards,Hongwei
On Saturday, 24 February 2024 at 00:59:34 GMT, Pedro Vieira (Gmail - Geral)
<pav.vie...@gmail.com> wrote:
Thank you for the quick response.
Based on the information received, it was possible to begin to understand what
was happening:
1) Proceed with self-calibration:
uhd_cal_tx_dc_offset --verbose --freq_start=3.45e+9 --freq_stop=3.55e+9
--freq_step=1e+6 --subdev=A:0
uhd_cal_tx_dc_offset --verbose --freq_start=3.45e+9 --freq_stop=3.55e+9
--freq_step=1e+6 --subdev=B:0
Calibration files were generated: tx_dc_F5B3E5.cal and tx_dc_F59F87.cal
2) In the uhd library I found the command uhd.types.TuneRequest. And in the
gnuradio library the command is the suggested example: uhd.tune_request().
However, I didn't notice any changes (see below)
Any ideas what I might be overlooking? Thank you in advance.
De: zhou <hwz...@yahoo.com>
Enviada em: sexta-feira, 23 de fevereiro de 2024 17:45
Para: usrp-users@lists.ettus.com; Pedro Vieira <pav.vie...@gmail.com>
Assunto: Re: [USRP-users] OFDM signal transmission by x310 presents a peak
Hi Pedro,
It could be DC leakage. Try to run the calibration commands. For X310, you need
to loopback connect Tx and Rx antennas with 30dB attenuators.
Regards,
Hongwei
On Friday, 23 February 2024 at 01:52:37 GMT, Pedro Vieira
<pav.vie...@gmail.com> wrote:
An ofdm signal, which is generated in python, presents a peak in the central
part of the spectrum. What could it be?
This same behavior appears on USRP X310 and HackRFOne.
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