[Al (astral highway)]

Hi Hugo

Originally Posted by Argus25

I assume that the design of your apparatus, when it is finished, would have a coupling coil around the main Tank coil, and in this case you would be using large valves to drive the coupling coil ?

Exactly. A coupling coil(tank coil) around the secondary coil, with the added complexity of a grid feedback coil and RC time constant elements.

Originally Posted by Argus25

In any case, one interesting thing about inductively coupling to a tuned or Tank circuit, is the loading of the driver circuitry on the coupling winding, can significantly up-shift the value of the resonant frequency of the Tank coil. But the effect depends on how tightly the coupling between the coupling and Tank circuit is and the impedance of the source driving the coupling coil.

For well coupled coils the effect happens because the damping on the coupling coil neutralizes some of the inductance of the Tank coil and that is what raises the resonant frequency above what you might get with a free resonance test.

So for example the valve's plate resistance driving the coupling coil can play a role in the final resonant frequency value, even if this parameter not officially a "reactive circuit element".

Interesting finding. Indeed, in my tests so far, a square wave signal into a coupling loop that is part of a resonant circuit, even when well below the apparent self-resonant frequency of the secondary coil, but coupled to it, will produce resonance. I think it is typically 0.7 times lower. Coupling is very tricky indeed.

I can produce a sketch of the generic set up of my apparatus but perhaps not on this threadm, as it takes away slightly from the emphasis on David Knight's paper, if that's ok?