Re: High voltage standing waves with a magnetron?

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

Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 

What you're describing is a fairly standard operation.. you're talking about
using a microwave oven magnetron to excite a resonant cavity of some sort.
It's a bit trickier than just coupling it in, because as the cavity power
goes up, power starts to flow back to the magnetron.  What you'd really want
is called a "resonant ring", which is something we use for high power
breakdown testing.  Conceptually very simple, it's hard to get to work: as
it heats up (and it does), the phase shifts change, so you have to keep
adjusting it to keep it working.
The trick is getting small power out of a magnetron. You can't just limit
the current and keep the voltage constant (because that's not the way tubes
work).  And, there's a certain threshold below which the magnetron won't
oscillate.

If you want to fool with microwave at low powers, there's a couple
inexpensive and easy ways.
#1... use one of those 2.4 GHz wireless TV thingies.  You can improvise a
probe with a suitable diode and antenna.  You can enjoy all the nifty stuff
fooling with a slotted line.  The problem is that 2.4 GHz is 12cm, so the
waveguide is big!

#2.. scrounge up a 10 or 24 GHz source as in a doppler door opener or
burglar alarm.  Then the wavelength is a more reasonable 1-3 cm.  You can
easily fabricate cavities and such with coffee cans, pipe, etc.
http://home.earthlink-dot-net/~w6rmk/radar10g.htm has some info on what I did
with one. (if the links are broken, let me know... I'm in the midst of
rearranging all my websites)

#3 look around for surplus microwave gear... it's there, and often quite
inexpensive.  Very few people are willing to make measurements with slotted
lines and sweepers anymore, since vector network analyzers make life so much
easier.

If you drop a bit lower in frequency (say, to 144 MHz), then you can build
open wire line out of copper pipe and such, and it's easy to come by sources
of several watts to 50Watts.


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, January 31, 2004 10:27 AM
Subject: High voltage standing waves with a magnetron?


 > Original poster: "mercurus2000" <mercurus2000-at-cox-dot-net>
 >
 > I was just curious if anyone experimented with high voltage standing waves
 > from a magnetron and trying to create a resonant rise from them? My idea
 > for a safe experiment, would be taking a small microwave oven magnetron,
 > power the filament at that standard 3 volts ac or dc, and applying
 > EXTREMELY small power HV DC current to the entire device, like 4000 volts
 > at a half a milliamp, to keep the power output at about 2 watts rather
than
 > the normal 1KW, would a circuit like this work? Or would the heating
 > current to the filament have to be reduced as well?
 >
 >