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hi lost_bro,
Very interesting! I'd read the first paper by Horst before but not the second, more important one.
I have a lot of comments, to keep them short I will bullet point them:
1) The circuits which switch static caps or inductors in and out of the circuit are similar to the one Barrow tested in the 30s, and the one that JLN and I tested in the 90s. Barrow is uploaded earlier in this thread. Switching artifacts are important to avoid of course. The JLN tests were crude relay tests, but later I repeated the tests with another experimenter using opto-isolated hexfets and also saw voltage spikes in the switched cap circuit. They were nothing like a parametric oscillation, but isolated voltage spikes, in the mV range, that were on the parametric resonance frequencies-- like they were trying to be oscillations. Although these were small in amplitude, they should not have been there at all under the test conditions, and I can only think that noise voltages present in the wire of the circuit were being amplified by the switching of the caps.
2) Barrow talks at length about antiresonance in his circuit, when the capacitors are switched so that their internal voltage is opposed to that of the circuit. Of course if an L or C is switched in and out of a circuit, charge or flux will be lost-- however it would be possible to switch the components into another tank when taken out of the first one, and this appears to be the only way that these types of circuits could conceivably get any serious output. As in the Barrow circuit, the total R of the circuit would need to be extremely low to allow parametric oscillations to happen at all under these conditions where zero voltage switching is used. Overall, I think these switched circuits are of scientific interest but not likely to get a powerful device.
3) More immediately useful is the case of varactor diodes. As Horst notes, the real issue that enforces reciprocality in these circuits is that the rising voltage of the parametric oscillations also changes the C of the varactors. Horst does use the hyperabrupt diodes which I consider the best candidate, because of their extreme nonlinearity. After much looking, I did find a class of parametric amplifiers/oscillators where output V was somewhat isolated from the varactors. I consider the best of these the circuit by Gunn, uploaded earlier in this thread. In this circuit, two high Q tuned circuits at different frequencies are used. An oscillation is started in the first circuit, which contains a varactor or several, which are biased by a step or ramp voltage over several cycles of the oscillation. At the end of this period, the frequency and amplitude of the oscillation are increased, and the energy is now tuned to the second tank circuit, and essential jumps over to that circuit, where it can be used. Gunn speaks of 'surges' of energy. As you can see, the output voltage swings several times from highest to lowest during one cycle of varactor bias. Maybe this isolates the varactor to some extent, since the varactor supply will see equal amounts of voltage increase and reduction? His varactors were of the old school type, with (typically) a C ratio of less than 3. I consider this circuit to be a good point for further experimentation, since Roberto Notte and I almost got self running even with the output oscillations fully interacting with the varactors.
4) Switching can also be very relevant to standard parametric oscillators where the parameter change is done at quadrature. The paper from Howson and Szerlip, attached, shows that if the parameter changing element is switched into the circuit only at quadrature (more or less) then the power gain of such amplifiers can be made infinite (contrary to the Manley-Rowe relation where the gain is limited to F2/F1). Pages 6 and on show the experimental work. This also may be a way of disconnecting the varactor (or other element) from the parametric output.
5) In inductive circuits, the parametric oscillation flux is such to create a loss in the drive power supply by raising the inductance when power supply current is at peak. Although the use of 'nullifying' output coils has been justifiable scotched as an OU mechanism in the case of inductive circuits, I still wonder about circuits where the output is created through parametric changes, and induction is cancelled by filtering. This is why I proposed an inductive circuit that uses two parametric oscillators in the output, whose fluxes are closely coupled and opposite. I can also vaguely see some ways that a varactor coupled with an inductor, as a unit, could be isolated in these ways...
6) I've collected a lot of parametric circuits, so I'm going to go back and really zero in on this issue of output voltage affecting the varactors, to see if somebody else has solved this problem. The word 'nonreciprocal' is often used with these devices, but I believe this refers to interaction between input and output signals, rather than the varactor itself. I still live in hope :-)
Fred
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Topic: parametric pumping of L's and C's (Read 48329 times)
