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Re: And what of the FCC?
---------- Forwarded message ----------
Date: Wed, 1 Oct 1997 19:31:32 -0700 (PDT)
From: "Edward V. Phillips" <ed-at-alumni.caltech.edu>
To: tesla-at-pupman-dot-com
Subject: Re: And what of the FCC?
"All of these posts regarding RFI etc have caused me to wonder:
What is the difference between a rotary gap TC and the prehistoric
rotary gap CW transmitters? Is it just a matter of tuning a TC to
deal with an antenna instead of a toroid or sphere as the "load"?
I have heard recordings of these signals from way back when, and I
can tell you that if the local birds sounded so melodious, we would
all spend our spare time outside blowing our feathered friends the
way of the Passenger Pigeon. If you have ever heard the Russian
Woodpecker on HF (shortwave, if you must), then I can tell you the
Woodpecker was much more agreeable of a sound. The Woodpecker was either
Soviet OTH radar, or a Soviet mind control device, depending who you
want to believe.
I dont know much about sparkgap transmitters, but I am pretty sure they
contained no active device, if you will, such as a vacuum tube.... so
mustn't they have been pretty much a TC? They were about the same freqs,
as I recall.
BTW, 500kHz is still very much an int'l distress frequency, the last I
heard. More of a ship freq than anything else, to my knowledge. So is
2182 kHz. Correct me if I am wrong tho.
Randy
"
1. The rotary gap SPARK transmitters were NOT CW. They generated
trains of damped waves, one for each firing of the gap. There
was an exception used by Marconi called something like his "timed
spark discharger", in which there was one spark per cycle of RF!
Took a very high speed wheel with many contacts to achieve that
effect at quite low frequency (of the order of 20 kHz).
2. The tone of a properly adjusted rotary gap transmitter could
be quite musical. I have heard the same tone from a TC with
rotary gap, but that was long ago. Don't know what the present
generation sounds like.
3. Spark transmitters - rotary gap, quenched gap, and straight
gap - were used at frequencies as high as 1500 kHz (200 meters
wavelength). At those frequencies the primary (oscillation)
circuit often consisted of a single turn of flat ribbon to allow
the use of a big enough capacitor to store the desired energy
(theoretically the POWER input of ham transmitters was limited
to 1 kW) per pulse at reasonable power transformer voltages
(typically as high as 20 kV).
4. The general configuration of a spark transmitter - primary
LC circuit with the capacitor charged from AC and discharged
with a spark gap switch, together with resonant secondary -
was indeed very similar to that of a "Tesla coil". In fact,
some of the old radio catalogs referred to the inductor for
an inductively coupled, two tuned circuit transmitter as a
Tesla coil. Would have to go through my collection to get a
correct citation. Certainly the name of Tesla was well known
in those days (circa 1905-1915).
5. As with Tesla coils, the peak powers were in the megawatt
range for the higher power transmitters. This is the reason
hams were able to communicate over hundreds of miles with
"low power" and crystal detectors.
6. The difference was that the transmitters were connected
to efficient radiating systems (the "radio engineers" in those
days fully understood the physics involved in designing and
building a good radiator), while the Tesla coil as discussed
here can be considered from the radiation standpoint to be
a very short helical antenna, for which the radiation resistance
is to be found in the handbooks. Spark transmitters employed
antennas from 1/4 wavelength to several wavelengths, which in
the case of a 100 kHz system would be 3 kilometers. "We" want
to dissipate the secondary energy in long and satisfying arcs
and sparks, while the radio/wireless objective was to dissipate
the power in the form of antenna radiation.
Ed