Richard Knoppow wrote:
I think Federal used the Poulsen arc converter, a
steady arc where this thing is more closely related to the
rotary arc, also used in early wireless. There were two
types of rotary arcs but both operated at much lower
interuption rates, typically at around 400 hz, and generated
the RF energy by means of tuned tank circuits.

The tuned tank circuit isn't generating the RF energy, it's just selecting
the energy you want.

Interrupt an arc and you get lots of harmonics tied to the interruption rate,
going way up. Run it through an RC filter and you can select the particular
harmonic you want to transmit, shunting the others to ground (and throwing most
of your power away in the process).

The Poulsen used a continuous arc which generated white noise.... you filter
that noise out and you get a signal that is narrowband... and the narrower you
filter it, the more power you lose. It's a lot less efficient than the rotary,
even.

Federal
Telegraph held Poulsen patents and exploited them in series
of wireless telegraph stations mostly on the West coast of
the USA. The rotary arc is not to be confused with the
Alexanderson alternator, a mechanical generator of low RF
energy. The alternator put out fairly pure CW. The
Alexanderson patents were controlled by General Electric and
were one of the main reasons for the founding of RCA after
WW-1, that is, to maintain wireless in the US under US
control.

The Alexanderson puts out a very nice note.... the problem with it is keeping
it on frequency, not phase noise. Oh, also keeping it from flying apart and
exploding is another issue. It's a far higher tech device and much more
difficult to make... and also not so effective at higher frequencies.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On 25 Apr 2010 14:57:32 -0400, (Scott Dorsey) wrote:

The Alexanderson puts out a very nice note.... the problem with it is keeping
it on frequency, not phase noise. Oh, also keeping it from flying apart and
exploding is another issue. It's a far higher tech device and much more
difficult to make... and also not so effective at higher frequencies.

There is still one functional station (operated one day each year)
http://en.wikipedia.org/wiki/Grimeton_VLF_transmitter

On Apr 25, 4:16 pm, Paul Keinanen wrote:
On 25 Apr 2010 14:57:32 -0400, (Scott Dorsey) wrote:

The Alexanderson puts out a very nice note.... the problem with it is keeping
it on frequency, not phase noise. Oh, also keeping it from flying apart and
exploding is another issue. It's a far higher tech device and much more
difficult to make... and also not so effective at higher frequencies.

There is still one functional station (operated one day each year)http://en.wikipedia.org/wiki/Grimeton_VLF_transmitter

Hey OM:
From:
http://en.wikipedia.org/wiki/Alexanderson_alternator

"Because of the limits of the number of poles and rotational speed of
a machine, the Alexanderson alternator is at most capable of
transmission in the lower mediumwave band, with shortwave and upper
bands being physically impossible."

Says it all?
73 OM
de n8zu

raypsi wrote:
Hey OM:
From:
http://en.wikipedia.org/wiki/Alexanderson_alternator

"Because of the limits of the number of poles and rotational speed of
a machine, the Alexanderson alternator is at most capable of
transmission in the lower mediumwave band, with shortwave and upper
bands being physically impossible."

Says it all?

The number of poles is part of the issue, but you'd think with modern
machining technology you could make a big rotor with maybe a thousand
poles. Problem is that if you do this, the capacitance kills you.

One possibility to run an Alexanderson alternator would be to run it
into a nonlinear device and then select one harmonic out. Again, it's
very inefficient....
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."