[Radio Wrangler]

Work on the assumption that most devices want to oscillate at any frequency at which they have even a glimmer of gain.

Work on the assumption that semiconductors keep being improved, their gain goes up, as does their frequency capability, so if you design anything intended to be manufactured over a decent lifetime, or repaired over ditto, you need to build in margin for friskier parts.

In a universe far, far away, someone created a theory that you need to return all ground connections to a single point or else you will suffer hum and noise pick-up due to ground loops.

In another universe far, far away in a different direction, someone created a theory that for stability at radio frequencies you need short immediate connections to a groundplane, or else you will suffer horrible oscillations and like Laurel and Hardy's chest of drawers, every time you close one, another pops open. Unused or supposedly unrelated parts and connections can get in on the act.

Here in our universe, both these theories are true. They look and are irreconcilable. So you have to compromise. The star ground threatens you with background hum and fridge clicks if you compromise on it. The groundplane threatens you with large oscillation, meltdown and drama if you compromise. You do have to compromise, but the threat levels say that the compromise is located nearer to the plane than to the star.

On top of this, you need to ask yourself what you've done to each individual device to stop parasitic oscillation.

For every feedback loop, you need to plan its frequency and phase response to engineer some stability margin.

Look upon these things as good housekeeping, good practice, and basic hygiene. Do them automatically every time. Do them thoroughly and don't wait for something to go wrong before you add them.

If you haven't designed in safety margins, then although your proto may work, you can run into trouble if it is ever manufactured or if anyone else builds one to your design, or if you have to change any parts.

This takes the self-discipline to put in parts which don't really seem to be needed. This is also an area where learning some maths pays off.

David