Performance at low LO frequencies

Hi all,

We were setting our system to work with a relative low LO and generate a simple CW tone. For this purpose we've set the LO to 90 MHz and feed a 20 MHz tone to obtain a 70 MHz output. To our surprise, the output signal seems to have a huge amount of spectral harmonics (due to the mixer between the LO and the input signal) and the signal at the oscilloscope looks terribly bad. Changing the input frequency for the tone didn't make the situation any better.

We wanted to verify this behaviour with the reference design and we got the same outcome (system being controlled by IIO tool). Even with higher LO frequencies (we tried several frequencies up to 1GHz), we see that the harmonics being generated become a significant part of the signal.

I wanted to know if this is a known issue and how to solve it? Please note that we are only looking at the transmitter side.

Kind regards

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