Frequency Halver

I'd forgotten that actual voltages are Vpk*Sin(), etc. Thanks for the subtle reminder.

Yes Fred. You've picked the only frequency-doubler sum that does not require squaring, and it is the use of Cos that keeps the output polarity honest. But generating Cos from Sin can itself be a problem.... easy at fixed freq, somewhat troublesome otherwise. Note that the relative phase shift has to be kept constant, whereas the amplitude has to be kept equal to Vin.

Something like that but possibly cruder.

I suspect that the Vout polarity remains positive (or negative) because of zero offsets in the cct.

A possible solution is to divide 2F by 2 and simply capacitively couple one output of the flipflop into the virtual earth of the summing amplifier. The small charge injections (at each zero crossing of Vout) should be large enough to overcome the offset, and alternately kick Vout into the opposing polarity.

doubler,

technique

use

the

really

an

maxima

instantaneous

tetrode.

You didn't halve the frequency of a sine wave, you used the input frequency to excite a tuned circuit that was resonant at roughly half the frequency of the input circuit, a much less direct relationship.

---------- Bill Sloman, Nijmegen

Too complicated. All one needs a non-linear device to feed a sub-harmonic oscillator that is set below the threshold of oscillation. Energy from the NLD fed to that "almost" oscillator will get it going. Like sitting in a swing that is still; the self-resonant frequency of the system can be excited by hand-pumping at twice the SRF, given sufficent energy; the hand-pumping is nonlinear.

Correct, but the result is essentially the same. And it will track frequency changes, apparently up to 10% and perhaps allows AM to pass thru as well (this last part i do not remember; been too long).

No circuit like this can halve the frequency of a sinewave. Any box that halves frequency has input values for which the output must have

Another way to look at is that single-valued linear+nonlinear functions make even and odd harmonics but don't make fractional harmonics.

That would be a divide-by-two flipflop!

John

It must have been a synchronized oscillator. No tetrode [1] will have an f/2 component of plate current when f is applied to a grid.

John

Now then Stevie boy, our magical disappearing original poster, since at this point you've failed to respond to assumptions ranging from the idea that you plan to use this 20 kHz to transmit secured data to using said

The usefulness of this thread will most likely continue to decline until more data is provided.

-- Rob

It's actually a hell of a circuit. In addition to providing near exact frequency halving of a 20 kHz input signal, it's highly immune to phase noise and jitter on the input. In fact, if you're a little bit off on the frequency of your input signal, it even corrects for it and still gives you the same output. For that matter, even if you're fairly far off on that 20 kHz the results remain much the same.

I did not describe that. I said that the plate was at ground, and that the input signal was applied to the plate. I also said that the power was extracted at negative gain from the grid, and that the second grid was at about 30V. The cathode, grid #1 are set up as a hartley (or colpitts) oscillator; grid #2 acts as the plate and is powered so the oscillator section is a bit under oscillation - ersonant frequency is one-half (ie: subharmonic of input). Please read what i originally described.

I like your non-converter!

Too bad you forgot to patent it; with the right marketing one could sell it for a few million or so...