[Radio Wrangler]

For a hands-on learning exercise, you have to try building several alternative types and compare them - built to comparable standards to keep the comparison valid. One oscillator alone tells whether that one works and what its performance is like but doesn't tell you whether another approach might have been different.

Building a lot of oscillators, and taking care over each one shows that the chosen circuit, IE the name, doesn't matter a great deal. You achieve stability by using suitably stable components and by diluting the variability of active device parameters by light coupling both in the driving and the sense paths. This latter comes down to scaling of values.

In quite general terms, the design choices which favour low phase noise tend to worsen temperature stability, and vice-versa. Though, there are ways to screw-up in one area without getting a benefit in the other.

The amplitude governing method in an oscillator relies on either driving an active device into cut-off, or into significant compression. It is remarkably difficult to make an oscillator which runs at low levels - especially one which can be relied on to start.

Some oscillators have a specialised level controller, a detector and a levelling amplifier controlling an AGC amplifier.

The BBC bought a number of HP 8656 synthesised signal generators to act as the RF oscillators for their world service transmitters. There's footage of one being operated, somewhere on the net

David