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Modulated Spark Gap.
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From: Robert W. Stephens [SMTP:rwstephens-at-headwaters-dot-com]
Sent: Tuesday, August 18, 1998 2:21 AM
To: tesla-at-pupman-dot-com
Subject: Re: Modulated Spark Gap.
> Tesla List wrote:
> >
> > ----------
> > From: Marcus Young [SMTP:MEYoung-at-uq-dot-net.au]
> > Sent: Tuesday, August 18, 1998 1:07 AM
> > To: Tesla List
> > Subject: Modulated Spark Gap.
> >
> > Hello All,
> >
> > Ive long been considering an idea for a spark gap with very prescise control.
> > It occured to me that controlling the movement in a gap could be achived
> > using the movement of a powerful voice coil and AF amplifier. This could be
> > used to trigger sparking.
> > I have thought that an AF voice coil/solenoid could push and pull on the
> > outer edge of
> > a centrepivoted disc via an insulating rod of some type, kinda like a
> > piston wheel.
> > A disc with electrodes arranged about the perimiter much as a rotary gap
> > has, but far,
> > far lighter in construction as centrifugal forces wont really be an issue.
> > Stationary electrodes would be positioned just outside the sparking range
> > of their 'humming'
> > counterparts while while at their resting positions. The 4 electrodes would
> > be configured so
> > as to fire a series break of 8 gaps.
> > Ive just never been sure what kind of solenoid/VC and amplifier Ide need to
> > move the small
> > but nasty weight of around four 4.5mm dia tungsten slugs back and forth 5mm
> > or so at
> > 0-1000Hz + without distortion.
> > There are 3 main advantages to this system, but also a few problems..
> > Advantages:
> > 1) Exactly controlled and easily measurable break rate/frequency with an AF
> > gen.
> > 2) 'On the go' controll over minimum gap distance by controlling amplitude.
> > 3) Easy to reference frequency to mains for perfectly phase-synchronous
> > operation (if desired)
> > *Maybe theres some advantage with different wave shapes but some things
> > are just meant for the lab...:)
> >
> > Disadvantages:
> > The problem with this gap is when you try to air quench it, this will most
> > probaly
> > cause problems with movement if the blast is as stong as it would probably
> > need to be.
> > *sigh* Any ideas anyone?
> > Has anyone ever made anything like this? It seems to have promise. I'm just
> > not in the
> > position to build one right now.
> >
> > Marcus
> >
> > ICQ! #15089999
Marcus, All,
I began to explore such a scheme about 2 years ago employing a 15
inch loudspeaker as a moveable piston which opened and closed the
spacing in a series gap employed with a conventional rotary break. My
desire was to modulate the streamer display in AM with recognizeable
human speech. By varying the holdoff voltage value of the gap system
in this fashion, amplitude modulation could be impressed as a varying
tank capacitor charge value before each break commutation. I was in no way
after or expecting quality sound.
According to Nyquist's theorem you can reproduce a signal like in the
is case human speech by sampling at a minimum of 2X the highest
frequency to be reproduced. There is a strong peak in human speech
energy at around 500 Hz. Therefore a rotary break with a break speed
exceeding 1000 PPS should do the trick. This technique is relatively
easy to accomplish with a small tabletop TC and gets more difficult
and expensive for a large machine. Operating a coil on DC BTW yields
far superior audible results.
Very crisp, clear hi-fi audio with a crackling hiss along for the
ride may be obtained by modulating a vacuum toob powered TC operating
on smoothly filtered DC plate supply. Several modulation schemes can
be used. Tips on how to do this can be found in any Amateur Radio
handbook under AM modulation methods for tube type transmitting
equipment. This is a particularly stunning effect for any
uninitiated visitor to the lab.
Robert W. Stephens
Director
Lindsay Scientific Co.
RR1 Shelburne, ON Canada L0N-1S5
Tel or AutoFax: 1-519-925-1771
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