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#14
September 30th 07, 12:45 AM
posted to rec.radio.amateur.homebrew
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Xtal calibrator, 1980 ARRL Handbook
In article ,
Uncle Peter wrote: "Mark Zenier" wrote in message ... In article , The problem here is that neon bulb relaxation oscillators top out at, according to the charts in the book, at between 10 and 30 kilohertz, depending on bulb type. Mark Zenier Googleproofaddress(account:mzenier provider:eskimo domain:com) I was curious if there was a limit on the upper frequency, and I was wondering about the waveform as well; that is if the circuit can produce strong harmonics up into the upper HF regions. It would be an interesting project to build! The book is pretty vague on the speed of a discharge. Neon lamps are sloppy parts. They age, their characteristics vary by how much illumination they get from other lights (or built in radiation), they take tens of milliseconds to settle down after they've turned off, etc. So the discharge speed is a pretty loose spec. Scanning the scope photo of a 7 kHz oscillation and feeding it into The Gimp (Linux's equivalent of Photoshop), it looks like the fall time of the sawtooth is about 30 microseconds, out of a total cycle of 140 microseconds. (A 4.7 meg resistor, a 50 pF cap, and an 5AB (a tight spec NE-2), at 140 volts). Even using just the steepest part, it doesn't look like there would be harmonics there much higher than 100-200 kHz. High impedance makes the waveform pretty squishy. Mark Zenier Googleproofaddress(account:mzenier provider:eskimo domain:com) |
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