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I am doing some preliminary tests to check the behaviour of two USRPs. The setup is simply an USRP B210 connected via cable to a N310. The B210 is sending a constant 1 at 2,48 GHz, the N310 is just receiving and saving the data to a file, both USRPs operating at a sample rate of 25,6 MHz. As expected, one can see the carrier frequency offset due to the LO frequency offset between the two USRPs as a result. However, there are periodic "jumps" that shift the signal up and down for some time. I am mainly bothered by the fact that these jumps happen instantly between two singular samples. What kind of effect am I seeing here?

The upper part of the picture shows the real part of the received signal, the lower part the difference between two consecutive samples. Received signal and difference between consecutive samples

When I reduce the carrier frequency offset it looks like this: Received signal with lower CFO

Thank you for your help, Michael

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I would guess it is some sort of frequency control, that automatically changes some of the circuit parameters to match the desired frequency.

It could be done through a lower frequency oscillator, that is then compared through divider or multiplier with the frequency of your 2 GHz signal.

If frequency is too high or too low, it takes time to notice it because of the frequency divider or multiplier, so the output looks rough.

Links that might be of interest:

https://en.wikipedia.org/wiki/Phase-locked_loop

https://en.wikipedia.org/wiki/Voltage-controlled_oscillator

https://en.wikipedia.org/wiki/Digital-to-analog_converter

You may check if these systems in your device have similar acting time to what you see, maybe it will help to you find which one is responsible for it more.

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