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Low powering magnetron

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LAN_403

Not Dangerous

Sat May 15 2010, 11:15AM

Registered Member #2859 Joined: Sat May 15 2010, 11:08AM
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Posts: 4

Hi. I'm italian and i don't know english very well, so excuse me :D
Btw, i have a magnetron taken from a microwave oven. I'm not sure that the magnetron works. I would try it at low power: i'm conscious of the risk delivered by the microwaves, expecally at high power (1000W), and I do not want do experiments with high power microwaves.
My idea is to turn on the magnetron at low powers, like 10 watts or minus. It is possible? if i will change the filament current can I reduce the emission power?

radiotech

Sat May 15 2010, 04:36PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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What do you want to do with the magnetron apart from the oven?

Lowering the filament current will lower the output power of the magnetron. Operating it with no load ( waveguide and oven cavity)
would damage it rapidly.

A good way to test the magnetron is to heat a cup of water
for a period of time and measure the temperature rise. This is a method shown in the service manuals for ovens.

Not Dangerous

Sat May 15 2010, 04:44PM

Registered Member #2859 Joined: Sat May 15 2010, 11:08AM
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Posts: 4

radiotech wrote ...

What do you want to do with the magnetron apart from the oven?

Lowering the filament current will lower the output power of the magnetron. Operating it with no load ( waveguide and oven cavity)
would damage it rapidly.

A good way to test the magnetron is to heat a cup of water
for a period of time and measure the temperature rise. This is a method shown in the service manuals for ovens.

sorry I expressed myself badly. I have been disassembled a microwave oven about 3-4 years ago. The microwave did no more heat the food, so it's a possibility that the problem was the magnetron.

My idea (powering the magnetron at low powers) is for experiment with microwave, not exatly to try if the magnetron works... if the magnetron doesn't work, i will retry the experiment with another one.

So, can a magnetron be low powered easily?

Proud Mary

Sat May 15 2010, 04:58PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Magnetrons have what is called a "theshold voltage" below which oscillation will not occur.

You will have to look at your magnetron's data sheet to find the threshold voltage, but you can be sure that operation at the threshold voltage will still produce potentially dangerous amounts of microwave energy.

I take the view that if you do not know even these most basic facts about magnetrons, you should leave them well alone. Microwaves from an oven magnetron could destroy your eyes in less than a second.

Leave well alone.

radiotech

Sat May 15 2010, 05:22PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546

You can experiment with microwaves safely and easily using transistors. A good place to look is ARRL publications and also Italian ham radio sites.

Not Dangerous

Sat May 15 2010, 07:05PM

Registered Member #2859 Joined: Sat May 15 2010, 11:08AM
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Posts: 4

Proud Mary wrote ...

Magnetrons have what is called a "theshold voltage" below which oscillation will not occur.

You will have to look at your magnetron's data sheet to find the threshold voltage, but you can be sure that operation at the threshold voltage will still produce potentially dangerous amounts of microwave energy.

I take the view that if you do not know even these most basic facts about magnetrons, you should leave them well alone. Microwaves from an oven magnetron could destroy your eyes in less than a second.

Leave well alone.

This is why i want power it at max 10 watts and in fact this is why i have opened this 3ad :D

I image the output intensity is proportional at the magnetron current, if i hold the standard voltage and i reduce the current does it work?

Not Dangerous

Sat May 15 2010, 07:06PM

Registered Member #2859 Joined: Sat May 15 2010, 11:08AM
Location:
Posts: 4

radiotech wrote ...

You can experiment with microwaves safely and easily using transistors. A good place to look is ARRL publications and also Italian ham radio sites.

microwave generators are based on high frequency oscillating circuit + antenna, right? in this case i cannot buid it

radiotech

Sat May 15 2010, 07:33PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546

microwave generators are based on high frequency oscillating circuit + antenna, right? in this case i cannot buid it

So is operating a magnetron-

Your tube cannot produce 10 watts. voltage * current * efficiency =
output power .

You might experiment with a 2.4 Ghz portable telephone and a very cheap microwave oven leakage tester like this one and the 3000 mHz frequency counter. Both can be bought for less money than a X-box video toy.

Kilham

Sat May 15 2010, 09:13PM

Registered Member #2814 Joined: Wed Apr 21 2010, 12:28PM
Location: Scotland, UK
Posts: 24

Go buy a Gunn diode and stick it in a bit of waveguide. Make sure you also have a high-speed Schottky diode so you can detect any output. It won't fry you but might get you into trouble for operating an unlicensed microwave transmitter.

hboy007

Sat May 15 2010, 09:19PM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
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Posts: 374

So you just want to build a low-powered RF source and reproduce some experiments. Even pulsed operation may be more dangerous as the average radiated power suggests. You may have to go a bit into the physics of wave propagation but you can construct the following: Mount the Magnetron onto a waveguide and then to a circulator, connect the next opening to a piece of waveguide that is too small for propagation of the lowest mode which will exponentially dampen the amplitude over its length and finish the circuilator with an absorber at the last port. You will mainly use this device as an electric stove but it is safe by design (once designed properly

). You can only increase ouput power by cutting off the output waveguide or in a hopeless effort to match waveguide impedance to free-space impedance. (match a complex impedance to a real one if you dare

sorry, this makes no sense)

If you choose to build the above setup, you will learn a lot, I promise

[edit] added missing words. Sorry for that.

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