Microwave Magnetron Projects

I recently inherited a microwave oven with a damaged door latch. The
magnetron works, but the rest of the oven isn't worth saving. Before I
cannibalize it for parts (like the HV supply and some kewl magnets), are
there any (safe and legal) uses for the working magnetron?

I'm ruling out microwave weapons, anti police radar devices, etc for
obvious reasons, but if there's something to be done with this before
destroying it, I might add it to my projects list.

Links to project web sites would probably be best. Thanks.

 

Ionize some gas maybe?

John

 

No. At that power level, literally anything you do external to the
oven box will belch dangerous levels of radiation.

The closest approximation of a safe application is a 2.4GHz ATV
xmitter:
<http://www.vhfdx.net/docs/mwpll.pdf>
<http://lea.hamradio.si/~s57uuu/mischam/magnetr/index.htm>
Note that the typical microwave power supply will not work for CW or
TV applications without considerable modifications. 100 watts CW at
2.4GHz is still a rather dangerous power level.

Remember, you have but one life to give to your profession.

 

See "RF Design" back sometime in 1989, I know I have a copy
somewhere. They modded one into an ATV Tx.

I'd be interested in something new and novel. I've gutted many over
the years, and usually strip them for the useful parts (microswitches,
control PCBs, HV diodes and caps, thermal switches, etc.) And the
magnets are very useful around the workshop. I've even made a
"magnetic broom" with 6 of them mounted on an old broom handle, great
for picking up errant nails, etc.

Barry

 

It would be nice to direct it into a large cylindrical cavity into which a
plastic bucket slides tightly. The bucket contains a solution you want to
heat, which for some reason must be done in this container (e.g., solution
reacts with metal or glass containers, or you don't have such, etc.).

The cavity would thus be open ended, but the water should be an effective
screen, as long as it's deep enough in the bucket.

Safety would of course be an issue, but interlock switches could be
provided for sensing that the bucket is firmly seated and perhaps a
dielectric sensor used to ensure the water level is always high enough.

And of course, the magnetron contains four potentially valuable things:
magnets, aluminum heatsink fins (a few cents), a solid copper body (maybe a
buck at today's copper prices) and a thermionic heater-cathode.

The middle two are nice to me, since I melt metals, and the last would be
nice to someone with a bell jar.

Tim

 

You might need some test equipment, say
http://gizmodo.com/gadgets/fashion/wi+fi-detector-shirt-self+detects-geeks-307516.php


Martin

 

http://amasci.com/weird/microwave/voltage1.html

I'll toss out one extra personal experience, too. In the last year of
high school, we had a science teacher with a masters in physics from
Northwestern University and a grand total of 7 students in the
advanced class. We used a klystron, not a magnetron, and the
wavelength you are talking about is about 5 inches I think, which is
somewhat shorter than what we were working with then. But we "beamed"
the klystron into the classroom from a desk on one side at a "crystal"
we'd built with tin-foil-wrapped Styrofoam balls stuck together with
sticks. These allowed us to use watt-meters, held by hand, to measure
different points on the other side of the "crystal", graph them, and
derive the diffraction patterns from the resulting measurements.

I remember some tinkering to get it running well and at the time I
didn't have any idea what a waveguide was, but it gave a great
hands-on, macro-scale understanding to how x-ray crystallography
works.

I'm not so sure I'd do anything like this with a 2.4GHz magnetron and
some adapted waveguide, blasting an open room in which I was wandering
around taking measurements. Also, your own body in this case may be a
problem, since you are mostly water and you could interfere way too
much with what you were trying to measure. So I don't think this
lesson would be safe or as useful an educational tool, unless you
found another way to take those measurements.

This comes from someone (me) who made "rocket candy fuel" from melting
potassium nitrate and sugar in a florence flask/beaker double-boiler
using boiling sulfuric acid as the bath to keep hot spots from forming
(melt temp was about 300C, flash point about 400C), and where I'm
nestled behind piles of sand bags I'd set up in the garage, just in
case. And that was only one of many different mixtures I experimented
with, including making mercury fulminate and nitroglycerin. So you
might consider a little, before you beam yourself or some hapless
volunteer with a dispersed 1kW beam of 2.4GHz at a distance of a few
dozen feet away.

No way would I do today what I was doing back then. (Or maybe I
really would, given half an excuse, and just won't say so in public.


Best of luck,
Jon

 

I'm not planning on running this thing outside of an adequate
waveguide/enclosure. So nobody has to worry about my survivors going
after the individual who provided me with the plans for a microwave
hairdryer. ;-)

One other thing: Its my understanding that the power supply for these
things is basically a constant current supply. The current is what
determines the magnetron's output power. If I decide its worthwhile to
modify the supply, I'm wondering how far the output of one of these can
be throttled down. I suppose the datasheet might provide this info. once
I get the oven disassembled.

 

http://mysite.verizon.net/resri52l/

Cheers,
James Arthur

 

maybe using a magnetron (since the cavity is resonant to wifi band)
and its small antenna inside complete to use it like a "driver" for
some "can wifi antenna" connected to some WLAN stuff ?

I was thinking about that, but could not find at that time at junk
yard some broken microwave oven ...

 

Paul Hovnanian P.E. posted to sci.electronics.design:

How about using it as the core of a humidifier?

 

It works pretty well to ionise Helium for a microwave induced plasma
as an ion source for ICP-MS, that is provided that you don't mind the
risk of catarracts, blindness and frying your kidneys. I once walked
into a lab where a senior researcher (who should know better) was
adjusting one with all interlocks off and the plasma fully exposed.
Surprisingly pleasing pale reddish coloured flame but I was out of
there instantly. About 1kW output and a spark to start the thing at
atmospheric pressure. eg.

http://www.ingentaconnect.com/content/sas/sas/2001/00000055/00000002/art00003

By comparison the RF ICPMS argon plasma flames are unpleasantly bright
and UV rich but nothing like as dangerous.

Anyone without the requisite knowledge to keep the microwaves safely
confined can expect to get some very nasty complications from
microwave exposure.

Regards,
Martin Brown

 

There are methods for doing so. The Next Big Thing in lighting is
microwave powered gas discharge lighting. No electrodes to wear out.

 

I hope not. None of them have come close to meeting FCC Part 15
unintentional radiator limits. The original microwave sulfur lamp was
originally promoted by Fusion Lighting in the mid 1990's. The FCC
sorta, kinda, maybe, somewhat killed the idea in 2003. Achrived web
site at:
<http://web.archive.org/web/20010209135028/http://www.fusionlighting.com/>

"Sulfur Lamps"
<http://en.wikipedia.org/wiki/Sulfur_lamp>

"FCC Rejects Satellite Radio's Petition to Ban RF Lights in 2.45 GHz
Band"
<http://www.rwonline.com/dailynews/one.php?id=6211>

"Fusion calls "timeout" in sulfur lamp race"
<http://www.iaeel.org/IAEEL/Newsl/1998/tva1998/LiMa_a_2_98.html>

Unfortunately, raising the dead is a common preoccupation in
electronics. LG and Island Systems Lighting(UK) have resurrected the
idea. Hopefully, it experience a quick product death.

Of course, there are less obnoxious forms of plasma lighting:
<http://www.thinkgeek.com/geektoys/science/964e/>
Powered by a USB port. I want one.

 

Build a sulfur lamp?

 

Says the sulfur bulb has a design life expectancy of 60,000 hours, and
that the magnetron needed to supply the microwaves has a design life
expectancy of 15,000-20,000 hours.
Meanwhile, I remember from elsewhere even shorter life expectancy being
usual for magnetrons - I generally got the impression of 10,000 hours.

I think that would support a contention that FCC did not kill the sulfur
lamp.

The Wiki article even notes that FCC in 2003 terminated a proceeding
started in 1998 that otherwise would have increased regulation of RF
emissions from sulfur lamp systems.

<SNIP>

- Don Klipstein ()

 

(Don Klipstein) hath wroth:

Google found claims of 2,000 hours for a microwave oven magnetron.
<http://gallawa.com/microtech/Ch7Pg6.html>
My guess would be even less based on personal experience with bottom
of the line consumer microwave ovens. I wonder if they have a runtime
timer built into the clock/timer circuitry?

True. I tried to be subtle. My opinion is that the FCC did not find
it expedient to do anything nice for XM or Sirius. The problem was
that they also had issues pending over their terrestrial repeaters and
Wi-Fi interference.
<http://www.computerworld.com/governmenttopics/government/policy/story/0,10801,69893,00.html>
<http://www.news.com/2100-1033-933965.html>
The satellite people are also having problems with the WiMax users:
<http://www.asteriskvoipnews.com/wim...ite_radio_interference_in_the_2_ghz_band.html>
<http://satelliteradiotechworld.blogspot.com/2007/09/xmsirius-reject-wcs-coalitions-proposal.html>
What the FCC apparently did was hand the interference issues back to
XM and Sirius with subtle hints that they should clean up their design
with better BPF filters and fix their own technical problems first.

In the case of the sulfur lamp, it was easy because during the 5 years
it took for the FCC to render a non-decision, Fusion Lighting dropped
the product and disappeared. There was no need to protect the bird
people from a non-existent product. The technical problem was that
there was no way Fusion Lighting could meet Part 15 certification
requirements. The bulbs leaked RF badly and no amount of RF shielding
seemed to be effective. However, that leaves the door open to other
companies to try and get it type certified.

Disclaimer: The opinions expressed are those of the author and do not
necessarily represent the hidden agendas and political intrigues of
the FCC.

 

Actually I would suggest that "raising the dead" by those who are well aware
of the initial causes of death is a very good idea: As technology advices,
many old ideas that were once impractical become quite viable.

I would agree that (too) many people "raising the dead" aren't even aware that
their "new" idea is quite old nor what the appropriate history is -- this
seems to be the case with some fo the folks promoting wireless re-charging
stations these days.

 

You remind me of my class D tube amp project.
http://webpages.charter.net/dawill/tmoranwms/Elec_Compound.html

I do wonder if anyone's ever done it before, you know, in history...

Tim

 

Sigh. I was afraid someone was going to take me seriously. Once upon
a time, I designed a radio direction finder, where the basic
principles were extracted from a 1920's radio physics book. I've done
other modernization projects, from electric car controllers borrowing
technology from about 1910[1], to borrowing overprice military
technology, that magically became affordable.

What engineering I've done in the past, is almost all "raising the
dead" if I include cleaning up someone else's mess, or picking up
projects after the funding died. For a while, my title was "Post
Mortem Engineering" in honor of my actual job function. Unfortunately,
my constant complaining was heard by management and whatever gods are
in charge of engineering, and subsequent projects turning into
cloning. Instead of raising the dead, I was now re-raising the
living. Sigh.

There's another benefit to raising the dead and reading up on old
technology. Many of the basic principles behind today's complicated
technologies are more apparent in the original crude forms, than they
are in the modern implementations.

Yep, but it won't help. Most new engineers want to do everything
themselves. Not invented here syndrome is epidemic. I did that for a
while, until I realized that reinventing the wheel was not a very
productive use of my time. So, I switched to the dark side and went
to "progress through plagiarism". The result was a large collection
of "Ideas for Design", competitors manuals, patents, old technical
books (which I still collect), and the usual reverse engineering. My
designs and career moved along much better after that, although there
was one problem. I never again had an original idea.


[1] Electric milk delivery vehicles were very popular between about
1910-1924(?) because they didn't make any noise during their early
morning delivery rounds.