On 09/01/2023 12:50, Ze Zhang wrote:
Hi all!
I was using two USRP N210 to send and receive signals and the distance
between the two antennas was about 20 cm. I sent three frames of QPSK
signals via a binary file.
On the receiving end, I found an envelope in the amplitude of the
signal that looks like a Sa function or a sine function. The first
figure shows the transmitted signal and the following pictures show
the received signal.
And after a spectrum analysis of the QPSK signal, it was found that
there was a low-frequency component in the signal (which could also be
a DC component due to the FFT frequency resolution). I would like to
know how to eliminate this effect.
Thanks in advance.
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You're running into the "DC anomaly" which is expected in
direct-conversion radio hardware.
You can use "offset tuning" to move considerably away from "DC".
Use a "tune_request" in your tuning that includes an offset frequency,
of perhaps 10-20kHz.
https://files.ettus.com/manual/structuhd_1_1tune__request__t.html
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