CW pulser

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CW pulser

Post by ChrisWhewell on Tue Dec 29, 2009 12:50 pm

I built a strobelight kit AK-520, which operates from two AA batteries. I pondered whether it might be possible to put together a tank circuit and put it in series with the xenon flash tube so that when the XE tube goes off, a powerful pulse of RF (of very short time duration) would be generated, and whether this concept might not be useful in constructing a lawful CW transmitter. If so, I'd expect perhaps that greater transmission distances could be achieved due to the high voltage used, even though the current is very low.

??

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Re: CW pulser

Post by Resistance is Futile on Tue Dec 29, 2009 1:54 pm

Without the strobe you are talking of the same concept a that was used by hams during the time of of 20s and 30s in what is called a spark transmitter, it was broadband and was finally put to rest as too many were objecting to its interference with other broadcasting.
And of course CW means Continuous Wave, which also would entail a amplitude modulation on the receiving end. A strobe would put out noise not a carrier wave.
The tank circuit would be used to fire the strobe?
or would the tank circuit be for the frequency out?
Why use a strobe when you could just use a neon transformer and accomplish the same objective. Of course you would have to have some kind of switching circuit in any design for your concept. And any electronics would have to be isolated from the higher voltages.
To achieve a strobe to fire you have to used a transformer to fire the strobe to start with.

Your Idea is a good one in concept, but you would run afoul of the FCC for excessive bandwidth.

One way you experiment and could find out the effect would be to use a fence charger. Turn your radio (portable) to a blank frequency on the AM band and see how far you can receive the noise from the fence.

Just my thoughts.
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Re: CW pulser

Post by ChrisWhewell on Tue Dec 29, 2009 2:41 pm

wouldn't the modulation occur on the transmitting end, and detecting being done on the receiving end ?

thanks Smile

Indeed the spark-gap generators, damped-wave oscillators of the days of old did bleed over into a lot of bands. I'm trying to figure a way to get the thing to only put out a pulse at a single frequency (of course harmonics can't be avoided). The tank wouldn't be used to fire the strobe, rather the coil of the tank would be in series with the high potential applied to the tube. I'd like to have a high amplitude pulse of short duration at a single frequency for and experiment I'm contemplating. But I should add that I often think of things that don't work !!

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Re: CW pulser

Post by Resistance is Futile on Wed Dec 30, 2009 12:36 am

I cannot see your circuit so its hard to understand your concept.

Yes modulation is created to transmit a CW carrier.
It is created without any information (Also called a dead carrier). The receiver injects a side tone (local oscillator)and is mixed into the receiver with the incoming signal.

From what I understand your saying is you want to put the strobe on one terminal of the coil in the circuit? The other end of the coil would go to the antenna?
The only thing that that would do is act as a key. A high voltage could be used but the best way and most efficient way is to have an Ideal SWR . High voltage and low current still has to obey ohms law for power.

There are transmitters that work on very low power (QRP) and can span the globe. These are called flea power transmitters in some circles. The antenna is designed to have the most efficiency for transmission. That would be the best solution. I am starting to get out of my knowledge base here, and others may have to step up to answer your queries.
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Re: CW pulser

Post by ChrisWhewell on Wed Dec 30, 2009 9:15 am

Its probably another example of a thought of mine that won't work, the Xe tube itself being merely a fancy spark gap. I appreciate your kind replies. Smile

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