Re: Tesla Coil RF Transmitter (long)

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Conner <steve@xxxxxxxxxxxx>

> The end is the radio systems that we use.
> Kilowatts of transmitted energy for microwatts of
> received energy not very far away.

I think this is a _very_ important point. The radio
systems we have now are direct descendants of Tesla's
wireless system work. People like Marconi found
empirically that if you use a long wire antenna that
radiates more of the power, it actually works better.

If you think about it, our current radio systems must
also be the best possible in terms of transmitting
power without wires. After all, to transmit a message
into the receiver you have to transmit power to it. So
the more efficiently it transmits power, the better it
will transmit information. The fact of the matter is
just that the amount of power you can transmit is very
small.

One example that might be of interest to world
wireless system fans:

The Radio 4 long wave transmitter in Droitwich,
England, puts out 400kW on 198kHz. This is about the
same order of magnitude as the powers and frequencies
Tesla was envisaging for his Wardenclyffe plant, to
start with at least.

Now the last Tesla coil I made just happens to
resonate at 198kHz. (It was a pure coincidence.) I
live 300 miles away from the transmitter. So how much
power can I pick up?

The answer, experimentally, is not a lot. If I plug
the base of the secondary into one antenna connection
of a radio receiver, and ground the other connection,
I get a storming good signal. I think I saw S9+20dB on
the receiver's signal strength meter after fiddling
with the topload to get it tuned. But that signal
strength corresponds to a captured power of only about
0.1 milliwatt. Hardly enough to light my house even
with phosphorescent tubes. :^)

Wired power transmission certainly wins here- my
nearest power station is a 2GW unit about 50 miles
away, and I can get 40 amps at 240V (10kW) any time I
want it. Even if the Radio 4 transmitter were 2GW, and
only 50 miles away, and I built the biggest antenna
that would fit on my house, you can see from the above
example that I wouldn't capture more than a watt or
two.

However, the same receiver- thanks to the wonders of
Tesla's resonant circuits- can give a usable signal
with as little as 10 picowatts. Under good conditions
you can receive a signal from a 100 watt transmitter
on the other side of the Atlantic. You can buy the
receiver and transmitter combined in a case the size
of a shoebox that runs off a 12 volt battery.

Of course, this is all old news to any hams, pilots or
ocean going yachtsmen out there ;) It's just an
ordinary HF radio set. They are fast being made
obsolete by satellite phones, but still good fun to
play with.

My point is that this is the state of the art, and I
recommend that anyone with an interest in Tesla's
wireless system should get themselves a ham licence
and have a play around. There is even a 136kHz ham
band now, so you can legally transmit on the same
kinds of frequencies as Tesla did using the same kinds
of antennas, and then try higher frequencies with
modern antennas and see how much better they work. ;)

I know there are other hams on the list. I have been
off the air for a long time but I just got hold of a
HF rig and I hope to see some of you on 17 meters as
soon as I get my station up and running.

Steve Conner, GM0TET