Mixing is a low noise way to generate higher frequencies since the noise powers of the two sources simply add but the spurious signals can be more trouble than the improved noise is worth. Frequency Dividers Frequency dividers will, in theory, improve the phase noise of a carrier just as a multiplier degrades the noise. In practice, logic devices are usually noisier than the better sources and the faster devices generate harmonics which can spread throughout a system. Bandpass filters may be needed on both the input and output to control the spurious frequencies. Mu-metal shields are often helpful.
Noisy devices can degrade power supply rails and can generate noise on grounds.
Try to control the current paths of noisy devices to keep the current away from sensitive components. Offending devices may include three-terminal regulators, logic, and motors. Some devices have high microphonic sensitivity and may require vibration and acoustic isolation.