AM Microwave Oven Klystron

"Brent Steven"

... Phil

..or 60Hz. Or is it double?

I think the OP should be able to draw a conclusion based on this.

Phil is likely right, and it's 50Hz (since the OP appears to be in Sydney Australia). Magnetron ovens magnetrons are usually powered via an unfiltered half-wave doubler, with or without a high frequency chopper.

HOWEVER, if it's a modern type such as Panasonic inverter type, it may be seeing a more steady voltage across the magnetron.

Best regards, Spehro Pefhany

There was a 5 page description in RF Design, mid 1990s, on using a 2.4 ghz ISM band maggie for ham radio video. It had 4 tubes in series with the magnetron for modulation. I cant find the reference right now but it is not hard to modulate one if ran on DC.

The other one that comes up is

Communications Quarterly's Winter 1991 issue has an article by WA6EXV

Most of them are very close to the 13 cm ham radio band and they have been explored for EME (moonbounce to non hams)

The downside for EME is unless you turn the cathode off and allow it to self heat once its running they have a very wide noise bandwidth on top of the center frequency. On the order of 10 mhz when driven off the 50/60 hz supply and pulsed. It goes down to 1-2 mhz without the cathode lit.

When I was in college I read the magazine stuff and just could not wait to duplicate the experiment, then I read up on microwave safety and decided I like my corneas clear...

Steve

March 1989, Pacholok, "A Microwave Oven to Amateur TV Transmitter Conversion," pp48-55.

A clearer schematic (electrically identical to Pacholok) by Bill Parker, W8DMR, was published in the Jan/Feb

Yep.

-- HTH, James Arthur

So, you say if I want to AM one at 300Hz, I simply need to plug a store-bought oven into a custom made 120V AC power supply running at that frequency?

How does this affect the efficiency of the magnetron, given it is designed for 50/60Hz? Is the current requirement the same?

Would the output resemble sinewave modulation on a CRO, or look chopped?

Thank you for your advice.

Brent Steven

Brent Steven schrieb:

Hello,

you should think not only about the magnetron, but also about the transformer supplying the magnetron. I think the magnetron is not designed specially for 50/60 Hz, but the transformer is. A transformer designed for 50 Hz will work with 60 Hz too, but not every transformer for 60 Hz will work without problems with 60 Hz. I saw a frequency generator from HP designed for 50/60 Hz power and also

Bye

On a sunny day (Fri, 27 Nov 2009 00:07:28 GMT) it happened snipped-for-privacy@radgrah.com (Brent Steven) wrote in :

Rotating vane in the wave guide.

"Brent Steven" claims he is from this mob in Australia:

How embarrassment......

This smug prick simply ain't content to stop at posting an embarrassingly dopey question on a matter he is utterly clueless about - he actually goes out of his way to show just how pig ignorant he really is.

But inserting his totally bonkers idea into another person's mouth.

But my generosity of mind may well be proved baseless.

I can hardly wait for the next instalment.

.... Phil

Converting a magnetron into a klystron is a non trivial project.

or

I think the inverter ones don't filter the rectified mains (at least not very much). There would likely be a large modulation at twice the mains. At least this is how the EMI from it sounds on a nearby radio.

Now that is very lateral :-).

The last (dead) microwave oven I opened up to see if there were any usefull parts had a constant voltage transformer driving a half wave si rectifier stack with very little smoothing at the other side.

If you want to amplitude modulate the output, you may need to substitute a full wave rectifier and more smoothing cap to get a more constant supply and less fm to start. Not sure if the magnetron would need to be derated, as the effective duty cycle would increase.

Jan's idea for amplitude modulation is probably the lowest cost and easiest to try though, but you should expect some fm as the effective load and vswr varies with fan position. I wonder if you could use a circulator in path to reduce the effect of this ?.

Regards,

Chris

I've seen a series-modulated maggie - it used a 4-400A that was literally in series with the magnetron. It would be almost impossible to implement this on a microwave the way they're connected in an oven, of course, but it's doable - I don't know how "clean" the signal was, because it was modulated with noise; it was a jamming transmitter in the USAF, so the output was intended to be terribly noisy.

But, series modulation _will_ work; I just can't make any promises about the quality of the output signal.

Good Luck! Rich

Here's one schematic that would fall into the "not very much" category:-

(page 20).

If you for some reason can't use a klystron (all you can afford is a magnetron, frinst), consider removing the magnetron's permanent magnets and winding coils to provide the magnetic field; you can then modulate their current. This basically takes the tube in and out of resonance, raising and dropping the output power. Slightly easier to modulate high current/low voltage than the other way around.

Just a thought.

Mark L. Fergerson

"Chris Quack"

Rectification is actually full wave, cos the magnetron itself acts as the other diode in the doubler - while the AC supply current draw is close to sine wave, rather than brief pulses at double line frequency as with most PSUs.

The deliberately large leakage inductance in the supply tranny plays a critical role in the operation of the circuit - as does the carefully specified high voltage filter cap of only a uF or two.

.... Phil

That's interesting. I can't remember if it had a resonating cap on the transformer, so perhaps that's how it worked. There was the usual cvt gap in the core, but don't doublers usually need two caps as well as 2 diodes ?...

Regards,

Chris

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It is surprising that they need that many discrete parts. The product is mass produced so cutting down on the parts count would be very worth it.