All,

I'm currently considering a design for making a steampunk radio. I
just
had an idea for the VFO that I want to run by those who have a far
better grasp of the abstract mathematics of harmonics than I do.

Suppose I have a DC motor running steady at 1000 RPM. Through a
X100 set of planetary gears I create a shaft spinning at 20,000 RPM,
which is pretty much the upper limit for small drills anyway. On
the
shaft is a disk that is an etched circuit board with a star pattern,
that is,
500 conductors etched radiating from the center to the edge of the
disk.

Now I have a wiper that is laid across the edge of the disk to make or
break contact with the outside of the star pattern, with 12 Volts DC
potential on the wiper. Assuming the shaft was conductive and made
firm contact with the center of the star pattern, should I see a 10
Mhz
square wave, suitable for say a switching mixer?

Question: How bad are the phase noise and harmonics likely to be?

Thanks in advance,

The Eternal Squire

The Eternal Squire wrote:
All,

I'm currently considering a design for making a steampunk radio. I
just
had an idea for the VFO that I want to run by those who have a far
better grasp of the abstract mathematics of harmonics than I do.

Suppose I have a DC motor running steady at 1000 RPM. Through a
X100 set of planetary gears I create a shaft spinning at 20,000 RPM,
which is pretty much the upper limit for small drills anyway. On
the
shaft is a disk that is an etched circuit board with a star pattern,
that is,
500 conductors etched radiating from the center to the edge of the
disk.

***
20,000 rpm, so how many revs a second?
20000 rev/minute x 1/60 minutes/second = 333 rev/second
How many spokes?
333 rev/sec x 500 spokes/rev = 167000 spokes/sec

Now I have a wiper that is laid across the edge of the disk to make or
break contact with the outside of the star pattern, with 12 Volts DC
potential on the wiper. Assuming the shaft was conductive and made
firm contact with the center of the star pattern, should I see a 10
Mhz
square wave, suitable for say a switching mixer?

No, you would see a 167kHz square wave, with plenty of odd harmonics:
500 kHz, 833kHz, 1170kHz etc.

Question: How bad are the phase noise and harmonics likely to be?

The harmonics speak for themselves. Mechanical rotation is hard to keep
constant.

Thanks in advance,

The Eternal Squire

You'rte most welcome

Brian W

The Eternal Squire wrote:
Now I have a wiper that is laid across the edge of the disk to make or
break contact with the outside of the star pattern, with 12 Volts DC
potential on the wiper. Assuming the shaft was conductive and made
firm contact with the center of the star pattern, should I see a 10
Mhz
square wave, suitable for say a switching mixer?

Question: How bad are the phase noise and harmonics likely to be?

Really bad, but the harmonics you can filter. Phase noise is going to
be way too high for anything but CW and your frequency stability won't
be anything to write home about. However, the system you describe was
built by Federal Electric in the 1920s, so it's at least practical.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

"Scott Dorsey" wrote in message
...
The Eternal Squire wrote:
Now I have a wiper that is laid across the edge of the
disk to make or
break contact with the outside of the star pattern, with
12 Volts DC
potential on the wiper. Assuming the shaft was
conductive and made
firm contact with the center of the star pattern, should I
see a 10
Mhz
square wave, suitable for say a switching mixer?

Question: How bad are the phase noise and harmonics
likely to be?

Really bad, but the harmonics you can filter. Phase noise
is going to
be way too high for anything but CW and your frequency
stability won't
be anything to write home about. However, the system you
describe was
built by Federal Electric in the 1920s, so it's at least
practical.
--scott

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. 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 Poulsen arc was widely used on board ships. The
device requires an atmosphere of hydrogen for the arc and
has a supply of alcohol to provide the gas by means of
disociation due to the arc. That gave the radio operator a
supply of drinkable alcohol which made the "sparks" popular.



--
Richard Knoppow
Los Angeles
WB6KBL

On Apr 25, 1:28*am, The Eternal Squire
wrote:
All,

I'm currently considering a design for making a steampunk radio. *I
just
had an idea for the VFO that I want to run by those who have a far
better grasp of the abstract mathematics of harmonics than I do.

Suppose I have a DC motor running steady at 1000 RPM. *Through a
X100 set of planetary gears I create a shaft spinning at 20,000 RPM,
which is pretty much the upper limit for small drills anyway. * *On
the
shaft is a disk that is an etched circuit board with a star pattern,
that is,
500 conductors etched radiating from the center to the edge of the
disk.

Now I have a wiper that is laid across the edge of the disk to make or
break contact with the outside of the star pattern, with 12 Volts DC
potential on the wiper. * Assuming the shaft was conductive and made
firm contact with the center of the star pattern, should I see a 10
Mhz
square wave, suitable for say a switching mixer?

Question: *How bad are the phase noise and harmonics likely to be?

Thanks in advance,

The Eternal Squire

Instead of mechanical contacts I would try an optical sensor but this
may not be very Steampunk. I have a friend who built a small steam
engine, for demo purposes he would run it on compressed air at 40K
RPM.

Jimmie

Jimmie

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."

It's been done: Have a look at:

An electro-mechanical RX for VLF.
http://www.wireless.org.uk/mechrx.htm

.............. Zim