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Simple Pulse Generator

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tektrical:
I've been looking at a patent for a simplistic high frequency pulse generator (US3798461A).  It's basically two disks spaced apart with a spark gap in the middle.  There's brass tubes in alignment, running out from the disks, with coax threaded through the tubes.  Each disk is connected to its own external capacitor, and when these caps discharge through the spark gap, the apparatus produces one pulse for each two sets of brass tubes, with the frequency determined by the length of the coax.  The number of desired pulses determines the number of tubes.

The patent says there is advantage to not stripping the coax, which indicates to me that the shield can be used for the central capacitive conductor, rather than the coax's inner wire.  This would provide a larger diameter, higher capacitance inner conductor than just running a normal wire through snug fitting tubes.

The patent also says an asymmetric output can be produced by replacing the lower tubes and coax with resistors joining the central conductors coming down from the top.  So the pulse output could be strictly positive or negative.  Then the length of the coax would be half of the output wavelength.  (It seems to me.)

With a lower supply voltage, the spark gap can be replaced with a diactor, or TVS diode.

For microwave frequencies, the device would be fairly small.  But water's specific dielectric resonant frequency can be produced.

And there will be a slight pause between the pulse strings, as the supply caps recharge.  This pause will be shorter with smaller, faster charging caps.

Steve:
Interesting....

tektrical:
Thanks, Steve.  I appreciate your interest.  And I am planning to play around with this, since it relates to more than one thing I'm working on.

The easiest way to get the discs is to use a safety can opener which slices off part of the rim when I open various sizes of canned goods.  And I just verified that electrical soldering flux also works on steel, to solder the tubes.

If I decide to do just some positive pulses, I may use the coax's shield itself for the tubes.  With, say, 10 holes in the can lid, I could bend some short pieces of coax into the upper part of a sine wave, solder the shield around the holes, and leave a little of the center conductor sticking down through the holes.  Then, short lengths of nichrome wire (from a hand held hair dryer) might work as the resisters, to tie the bottom circuit together.  The part of the coax which has the bend will have to be stripped, leaving the inner wire bare.

massive:
never opened a hair dryer. I have an old HV unit which has what I assumed was a resistor arrangement, which by memory broke which is why I haven't pulled it out for years. might go check that.
from my years of reading , 1/4 wave length has always stuck with me because of zero to peak. just referring to what you mentioned 1/2 wavelength

tektrical:
As I understand it, each tube produces a 1/4 of each pulse wavelength.  The potential goes up through one tube, then down through the adjacent tube before reversing polarity.  A single tube version could be great for some applications.  (This was the original inspiration for Ed Gray's Conversion Tube).  From a relative perspective, a unit whose wire is a quarter longer than the length of a coil's wire will produce a rotating magnetic field when the signal is applied to the coil.  Ideally, the coil could have four or five turns.  But a single turn coil will also work.  Or several turns, if you want a stronger field and don't mind the wire length and/or want to keep the frequency lower.

Another good place to get resistive wire is from the heating elements in a toaster oven.

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