[Discuss-gnuradio] Calibrating frequency offset between Tx and Rx in GRC (USRP B210)

[Inkyu Bang]

Hi, all

I am trying to calibrate frequency offset between Tx and Rx (USRP B210) by manually using GRC.

First, I have checked self RF-calibration UHD functions but it seems B210 does that internally.
ref: http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/2016-June/020750.html

Q1) How can we compensate some frequency offset between Tx and Rx devices using GRC?
Is there any simple way to do this?

For this, what I have tried is to send simple sine wave and then checked how the frequency of sine wave is changed at the receiver side.

For example, I sent "sin(f0)" using a carrier frequency "fc" and I received "sin(f0+f_delta)"

I can clearly see f_delta using QT_GUI_TIME_SINK block.
sampling rate: 5MHz
center frequency (fc): 5.89G
signal frequency (f0): 5000Hz
tx signal (5 peaks): https://imgur.com/r8BXGI2
rx signal (6 peaks): https://imgur.com/NO462Vd

To figure out the f_delta, I tried to use FFT (QT_GUI_FREQUENCY_SINK) but it's hard to figure out f_delta for me (I used 8192 FFT size).

Q2) Can anyone help to solve this problem?

The last question,

I transmit simple sine wave using different USRPs (separately).
it shows different received signals.
(i.e., USRP1 to USRP_rx or USRP2 to USRP_rx)

Q3) Is it simply due to different tx frequency offset between two devices (USRP 1/ USRP 2)?

sampling rate: 5MHz
center frequency (fc): 5.89G
signal frequency (f0): 500Hz
tx signal (USRP1): https://imgur.com/SCW8dAX
rx signal: https://imgur.com/AvplL8O

tx signal (USRP2): https://imgur.com/SCW8dAX
rx signal: https://imgur.com/w5ER332

Thank you,
Regards,

Inkyu