"terry" wrote in message
...
On Apr 25, 11:31 am, brian whatcott
wrote:
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- Hide quoted text -

- Show quoted text -

Sounds like re-inventing the Alexanderson? rotary alternator
transmitter in Scandinavia?
By the way 167 thousand cycles (167 kilohertz). Is right in
the
European 'Long Wave' broadcasting band! For example BBC is
on 198
kilohertz just slightly longer than 1500 metres wavelength!
(1515
metres).
Not sure what is the point of electromechanical frequency
generation?

More like the rotary arc. The Alexanderson was a
high-frequency alternator producing pretty pure CW. Several
very large ones were built (200KW) operating at long
wavelengths, perhaps up to a couple of hundred Khz. Some
remained in service for decades.
Rotary arcs were used to generate modulated waves, so
called MCW so that the detected code could be read without a
modulator at the receiver. Typically they had interruption
rates on the order of 500 hz. They were often called "rock
crushers" because of the terrific mechanical noise they
made.


--
Richard Knoppow
Los Angeles
WB6KBL