DISSOCIATING WATER, A KEELY Project

[hansvonlieven]

Sorry all,

I forgot to add the link in my previous post.

http://www.zen22142.zen.co.uk/spice/ammod.htm

Thanks argona, will check it out

Hans von Lieven

[Mr.Entropy]

http://www.zen22142.zen.co.uk/spice/ammod.htm

Hi Hans,

Are you sure that amplitude modulation is what you want to do?  I don't know what Keely was up to, but I can tell you that generating a 43KHz carrier, nicely amplitude modulated by audio frequencies, would be really hard to do by mechanical means, and isn't the sort of thing you could do with resonators.

If amplitude modulation is what you want to do, then the circuit you posted probably won't suffice.  It needs a very large difference between the carrier frequency and modulation frequency to do a good job, and your carrier frequency really isn't high enough for that.

You'd be better off making a modulator based on a good balanced mixer like the popular SA612:

http://www.nxp.com/acrobat_download/datasheets/SA612A.pdf

it isn't hard to find modulation circuits of many sorts using this chip on the web.

Cheers,

Mr. Entropy

[hansvonlieven]

G'day Entropy,

I really would like to try an ultrasonic carrier in the 40 to 50 KHz range just because it has been bandied around so much. I am not convinced it will help though it has to be attempted even if only to debunk an old idea.

So, here is another design for an ultrasonic transmitter that might just do the job I have in mind. Let me know please what you think.

Hans von Lieven

[Mr.Entropy]

Hi Hans,

So, here is another design for an ultrasonic transmitter that might just do the job I have in mind. Let me know please what you think.

That one looks quite good.Ã,  Note:

1) you should adjust the filter after the relaxation oscillator if you change the carrier frequency, to keep the carrier nice and sinusoidal.

2) If you're modulating with a PC sound card, you're not going to need the microphone amplifier.Ã,  Or you could just swap R2 for a larger-valued resistor to reduce the gain but keep the gain control.

I really would like to try an ultrasonic carrier in the 40 to 50 KHz range just because it has been bandied around so much. I am not convinced it will help though it has to be attempted even if only to debunk an old idea.

The carrier is fine.Ã,  It's just amplitude modulation that's weird.Ã,  I'd expect a system of resonators to create a simple superposition of the resonator frequencies.Ã,  When you do amplitude modulation, you actually change the frequencies produced.Ã,  Putting frequencies A and B through a multiplier outputs frequencies A+B and A-B.

I ask, because its actually possible to make a modulator that allows a _stereo_ PC sound card to produce _any_ arbitrarily complex sound in any 30KHz band (i.e., 20-50KHz, 15-45KHz, etc.).Ã,  So if AM isn't really what you want, you have other options.

Cheers,

Mr. Entropy

[hansvonlieven]

Thanks Entropy,

Electronics isn't really my bag, I understand it in broad strokes, but when it comes to detail I am way out of my area. I really appreciate your help.

Hans von Lieven