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Author Topic: 2.4GHz Amplifier From Microwave Oven Magnetron?  (Read 31606 times)
LETTERX
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« on: September 09, 2010, 07:28:40 PM »

How hard would it be to build a 2.4GHz power amplifier from a microwave oven magnetron?  I need to extend the range of my WiFi router.
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KE3WD
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« Reply #1 on: September 10, 2010, 05:12:22 AM »

Geez this is gonna be a THREAD...

Have at it, ehams! 

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K2DC
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« Reply #2 on: September 10, 2010, 05:25:51 AM »

I would think the appropriate first question should be "Is it legal to build a 2.4GHz power amplifier from a microwave oven magnetron to extend the range of my WiFi router?"

73,

Don, K2DC

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LETTERX
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« Reply #3 on: September 10, 2010, 06:24:59 AM »

The part about the WiFi router was actually sarcasm (grin).  I'm sorry if that wasn't apparent.  That said, I am truly curious about the possibility of building an RF amp from a used microwave oven.  Is this even possible?
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W6RMK
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« Reply #4 on: September 10, 2010, 08:16:28 AM »

Kind of tricky.. The magnetron in an oven isn't designed as an amplifier, but as an oscillator.  You can injection lock it (as well as controlling frequency by changing the voltage to a certain extent).  As you can imagine, they're not really designed for nice quiet RF.  In oven use, they're run off a half wave voltage doubler, so they actually pulse at the line frequency. 

However, there's a paper out there by a guy who ganged a whole bunch of them together to create a microwave weed killer (googling for that phrase will probably turn up the paper)..

If you wanted to operate CW or wideband FM, you could probably rig up some sort of suitable modulator.  You'd want a different power supply for the HV, and that gets tricky.. I don't know whether they would run at a cathode voltage (they run anode grounded) that is continuous that would be comparable to the pulsed higher voltage used in oven service. 

If you have a suitable HV power supply to fool with, you could find out pretty quickly.  The existing MO transformer is pretty sketchy.. they're designed to be cheap and don't have a lot of headroom: core cross section is small, wire is as thin as they can get away with, etc.   Work fine if you've just got the filament load, though.

(oh yeah.. be careful about RF exposure.. don't look into the waveguide with the remaining good eye, and all that)
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LETTERX
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« Reply #5 on: September 10, 2010, 10:23:09 AM »

However, there's a paper out there by a guy who ganged a whole bunch of them together to create a microwave weed killer (googling for that phrase will probably turn up the paper)..

Found that paper here:  http://typnet.net/Articles/WeedKiller.pdf   
Yikes!  Looks like an absolutely horrific device.  Twelve 800W magnetrons slapped into a large sheetmetal enclosure that creates twelve horns pointing at the ground.  Powered by a 400 V AC, 50 kVA generator run from a tractor motor.  This large contraption is pulled across the ground to kill weeds.  Freaking scary monstrosity of a thing. 

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TANAKASAN
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« Reply #6 on: September 11, 2010, 08:12:53 AM »

Anyone considering messing around with magnetrons should abandon plans to have children.

Tanakasan
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W0BTU
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« Reply #7 on: September 11, 2010, 09:21:21 AM »

Why don't we just drag a microwave oven to the top of our tower, disable the door switch, and open and close the door to send CW?  Wink
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KH6DC
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« Reply #8 on: September 11, 2010, 04:34:12 PM »

Wouldn't it be easier to go to Best Buy and buy an extended range wireless router?
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73 and Aloha,
de Delwyn, KH6DC
N2EY
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« Reply #9 on: September 12, 2010, 05:50:22 AM »

How hard would it be to build a 2.4GHz power amplifier from a microwave oven magnetron? 

Very.

73 de Jim, N2EY
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G3RZP
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« Reply #10 on: September 12, 2010, 09:00:47 AM »

Some years back, there was an article in one of the magazines about building a 2.4GHz tx from an oven. What should be pretty easy (!) is to build a pulse position modulated supply, and use PPM with the magnetron. It would be pretty dirty, but would meet FCC regs with a suitable waveguide filter for the harmonics.

Might take out all the neighborhood's WiFi, but who would know who is responsible? Additionally, as a part 15 service (which WiFi is in the US), quite likely the FCC wouldn't worry about interference to it from a licenced station - provided you met the radhaz requirements.
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W6RMK
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« Reply #11 on: September 12, 2010, 11:06:49 AM »

Then, the challenge would be in finding someone with a PPM receiver to work.. but hey, that's what ham radio is all about: gotta start somewhere.

Actually, some sort of pulse frequency modulation might be a better approach.

However, the OP asked about turning a oven magnetron into an amplifier, and that's real hard.
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G3RZP
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« Reply #12 on: September 13, 2010, 04:22:23 PM »

>However, the OP asked about turning a oven magnetron into an amplifier, and that's real hard.<

I hate to say 'impossible', but I would think very, very near it. Maybe if you had a microwave tube manufacturing facility, but then why would you try with an oven maggie?
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N3OQD
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« Reply #13 on: September 15, 2010, 05:06:09 AM »

I looked at that "weed killer".  Looks like a magnetron from hell waveguide assembly.  I wonder if the guys that were standing around during the tests can still father children.  As far as extending WiFi, it is allot easier (and far safer) to get a long range WiFi device made for the purpose.  There are allot of creative home made WiFi dish projects that utilize a thumb drive WiFi (fed at the focal point of a "dish")that many experimenters have had some success with.  Lots of stuff on the web about them too.
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K7GRR
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« Reply #14 on: September 25, 2010, 03:42:10 AM »

Having been a high power ( >1MW ) radar tech, and having seen a small radar built around a microwave oven maggi, you really, really don't want to mess around with this as an amplifier.  There are far better/safer ways to do this without the risks, and with a greater chance of success.

BTW, with a 600mw 802.11b/g AP from Ubiquiti Networks and a 20db dish antenna, you can establish a wifi link of several miles (manufacturer claims tens of miles), and still be OK with the FCC regarding EIRP in that band.  For well under $150 per node.
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