Dr. Grok wrote:
Zeners are also often used as noise sources, which might be a good reason NOT
to use them for the tuning, especially in a receiver.

You mean that a zener diode biased at less than breakdown voltage
generates more noise than a diode specified for varactor use biased at
less than breakdown? I assume this noise would be in the form of time
jitter of the capacitance, since the leakage current would be very
small. Have you seen this in some specification, or is it from experience?

Roy Lewallen, W7EL