Re: SSTC As a transmitter.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Gary Peterson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <glpeterson-at-tfcbooks-dot-com>

> > Also (back on topic!), next time I set up my large coil I'll tune
> > it down to 60kHz with a tractor tyre and see how many volts I get
> > from Rugby MSF.
> > --
> > Paul Nicholson

> I don't know how much power "Rugby MSF" runs, but I live about a mile
> and a half from a 50 kW local BC station on 1430 kHz.  I can develop
> about 30 volts DC at the output of a crystal receiver when I tune to
> them.  I can also get about 250 ma RF current when I series tune the 50
> foot vertical antenna I am using.  The output of the crystal set is to
> give surprising volume out of a speaker, but the actual power delivered
> is still only a few milliwatts.  I suspect that your large coil doesn't
> have an effective height anywhere near 50 feet.
>
> Ed

When using a Tesla coil as a receiver it helps to elevate the topload a few
feet above the top of the resonator.  I have found it convenient to mount
both components on a single piece of 2 1/2" white PVC pipe.  The pipe itself
has three hardwood legs, 6 pieces of 22" x 1' x 1/2", fastened with 1/4" x
20 brass bolts to form a tripod.  I use a home-made thin wall coil form with
Plexiglas disks top and bottom, both having circular holes at their centers
to accept the pipe.  Of course, spark breakout is not an issue for a
receiver topload.  I have started out using a long piece of 18"-wide
aluminum foil on a wooden roller assembly.  A few inches of the free end of
the foil is rolled on to a 20" wooden batten and then sandwiched with
another batten.  A piece of light nylon line is attached as a pull, and the
entire assembly is mounted on a vertical section of 1 1/2" black PVC pipe.
I use a coupling and slip bushing the mate to the 2 1/2" pipe.

The bottom turn of the resonator is 18" off the ground.  The coil is
connected to the topload with the same gauge wire as used for the coil,
connected at the top to strip of springy metal which bears on a slip ring at
one end of the roller.  Tuning is accomplished by pulling the foil out from
the roller like you would a window-shade.  This arrangement has its' pros
and cons, but it works well, especially if there is no wind.  One difficulty
is the need to tip the whole apparatus to its' side in order to roll back
the
foil when you tune past peak resonance.  Rather than wasting time with the
fix, I am moving ahead, building a more robust elevated cap assembly which
will allow a topload of fixed dimensions, a disk, a sphere or whatever, to
be raised and lowered at will.  I'm handling the resonator-cap connection
with a wire festoon.

Of course, the circuit has to be grounded.  I have achieved good results
using a fire plug/hydrant.  I have been using a piece of insulated #12 cord
about 25 or 50' in length laid on the ground to make the connection.  As for
output, I prefer to bypass the short secondary and capacitively couple
directly to the excited circuit.  While a voltmeter works, it lacks
selectivity.  I prefer to use a long-wave receiver and tune to the frequency
of interest.  It's placed on an wooden table about 6 ft. away, and a lead is
connected from the receiver's ground terminal to a common grounding point
fastened to one of the tripod legs.  A second lead is run from the
receiver's antenna terminal to a point on the vertical PVC pipe about 2 ft.
above the top turn of the resonator.  Try adjusting the coupling for effect.

Nearby objects such as trees and buildings have a noticeable effect on
tuning, so get as much out in the open as possible.  You'll find you have to
step back from the coil to get maximum resonant rise.  Watch the S meter as
you move forward and back, as this helps with fine tuning.

Tesla on the receiver:
    "If you take this fourth circuit [the secondary] entirely away, and
leave only that circuit here, the antenna and the ground connection, then
that is the ideal condition for the flow of the current in this receiving
circuit.  Any other circuit you bring near to that excited circuit with the
antenna will draw energy from it and tend to pull down the oscillation in
the latter circuit and diminish the resonant rise.  No matter what you link
to the antenna circuit, and how you link it, the energy you take away from
that circuit will always tend, being frictional, to diminish the resonant
rise.  Now the art consists in reducing as much as possible the energy
necessary for the signal, and in that regard the evolution of detectors as
the audion of Dr. De Forest, and of other such devices, is in the proper
direction, rational, and good.  But the ideal condition requires that you
should have here a device which only requires pressure and no current; and
once you have a device which does not need any current but merely acts by
pressure and has no internal capacity, so that there will be no capacity
current in the circuit, then that is the ideal receiver.
     "There are two ways in which you can operate if you have a receiver of
that kind.  One is by linking, closely, your working circuit with the
primary excited circuit.  The other is by linking it loosely, and then
working up the pressure by resonance.  You will find that you can do much
better, if you have such a device, to produce the necessary pressure by
turns, than by resonant rise, because if you want to excite it by resonance
you have to link only a few lines; start with a very low electromotive force
and work it up.  But, if you have such a device as I have described, you can
obtain any pressure you like by a few secondary turns.  I have invented such
an instrument and have  demonstrated its efficacy."


Gary