When is a Butler not a Butler ?

Sounds like it's set exactly right...

I think you're making an error along the lines of Tesla: resonances aren't unlimited. Jim said the Q is known and the drive is known, so you get a voltage divider between the Thevenin output impedance of the amplifier and the resistive loss component in the tank. For constant current drive it's even simpler, V = I*R.

Such a circuit could be hard to start, but a hysteretic drive should do it quite nicely. Although, gain is then very large (indeed, greater than infinity, so to speak, due to the positive feedback in excess of the open loop gain), so it must be limited by the driver stage. In that case, the output impedance (to the tank) is limiting it, with much harmonic content of course, which is mostly attenuated, depending on Q.

Tim

No, if there is an error, that one isn't it.

Consider the general case of an oscillator consisting of an amplifier and a tuned element:

In order for oscillations to build up, you need a gain around the loop that is greater than unity. In order for them to remain stable, you need the gain around the loop to be exactly unity. Something must reduce the gain.

In most oscillators, the signal builds up until something goes nonlinear. In some there is an AGC action that is nearly linear as far as the RF is concerned. This is usually done by having the RF amplitude much smaller than the bias variations used to control the gain.

Hysteretic drive is by its nature non-linear. It is one of the sort of nonlinearities that are used to set oscillator amplitude. In this case it is one that is mostly used in RC oscillators because it also remembers the past.

Well then there you go, I think.

Tim