Generally, the harmonics below 5th order should be reserved, otherwise the waveform will be too flat.

If there is a shaping circuit at the back end, it can filter out more than three harmonics; If there is no shaping circuit at the back end, it is recommended to filter out the higher harmonics above 9 or 1 1.

Please also note:

5M is usually a high-stability crystal oscillator with standard frequency. If it is a highly stable crystal oscillator (above 0.05ppm), adding filter shaping circuit will introduce more phase noise.