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Old 20th January 2011, 05:54 AM   #1
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Default The Magnetron - A Low Noise, Long Life Amplifier????

Folks, I found this document a number of years ago, skimmed though it then put it away on my HD. Dusted it off today, and here I am.
What is this? IS it really what it says it is?

http://72.52.208.92/~gbpprorg/mil/he..._amplifier.pdf

It says 30db of gain. How can this be? Can this be a low noise audio amplifier or not? Any ideas?
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Old 20th January 2011, 05:57 AM   #2
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Not for audio, strictly microwave frequencies.

Gary
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Old 20th January 2011, 09:19 AM   #3
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Still nice if you want to build a home radar station though!
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Old 20th January 2011, 10:44 AM   #4
Doz is offline Doz  United Kingdom
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Still nice if you want to build a home radar station though!
... that sort of comment makes my blood boil
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Old 20th January 2011, 12:15 PM   #5
DF96 is offline DF96  England
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The magnetron is a narrow-band amplifier, with the frequency range set by the mechanical features of the valve i.e. a 2.4GHz magnetron can only amplify 2.4GHz. A 1kHz magnetron would have to be roughly 2.4million times bigger!

"Low noise" in this context means low noise as a transmitter, not necessarily low noise as a receiver. People don't use magnetrons as receiver preamplifiers!

30dB gain is nothing special. An ECC83 can give a gain approaching 40dB, EF86 even higher. I'm not sure what all the excitement is about.
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Old 20th January 2011, 03:50 PM   #6
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An ECC83 can give a gain approaching 40dB, EF86 even higher. I'm not sure what all the excitement is about.
An ECC83 or EF86 can not produce any gain at all in the 2.4 GHz region, nor could it produce 500+ watts of power. The magnetron is designed to be a self oscillating power source useful in radar and RF heating (microwave oven). This is the first time I have heard of one being used as an amplifier. Even today 500 watts of power at 2.4 GHz would require several hundreds of dollars worth of silicon, GaAs or GaN.

As stated, not useful at all for audio though.
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Old 20th January 2011, 04:04 PM   #7
DF96 is offline DF96  England
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Yes, I was surprised at a magnetron being used as an amplifier. It seems the author uses it as a locked oscillator via a directional coupler.

I was not suggesting that ECC83 could be used at 2.4GHz, just that audio gain of 30dB is unremarkable. Maybe I misunderstood the "wow!" factor in the original post?
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Old 20th January 2011, 04:44 PM   #8
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Originally Posted by CivicProtection View Post
Folks, I found this document a number of years ago, skimmed though it then put it away on my HD. Dusted it off today, and here I am. What is this? IS it really what it says it is?

http://72.52.208.92/~gbpprorg/mil/he..._amplifier.pdf

It says 30db of gain. How can this be? Can this be a low noise audio amplifier or not? Any ideas?
It would seem to really be what it says it is. However, it has no audio applications at all. Although, if you could remove the magnet from a magnetron you might be able to use it as a single ended diode. That's about the extent of it.

It isn't anything you'd want to fool with. The frequency mentioned here, 2.4GHz, is right in the middle of aviation frequencies. Though the FCC has been an absolutely incompetent and useless gov't agency, for the past 30 years. It has existed mainly as a source of patronage jobs (Colin Powel's son was once its head, though his radio experience was nil) it refuses to enforce illegal fish net buoys (exceeding legal power limits, and operating well off-frequency -- these things have totally ruined the 180M ham band completely) that are openly sold in virtually every fishing supply store up and down the West Coast, and the US of A is the only developed country in the entire world without a long wave ham allocation. You can get away with running "pirate", "illegal" radio equipment and they won't do anything about it. The FAA, on the other hand, gets real fussy if you start screwing around with their frequencies.

Fire that up, and you can be sure that the men in black suits will come a-callin'.
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Last edited by Miles Prower; 20th January 2011 at 04:52 PM.
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Old 20th January 2011, 05:54 PM   #9
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Smile nothing unremarkable for audio

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Originally Posted by DF96 View Post
Yes, I was surprised at a magnetron being used as an amplifier. It seems the author uses it as a locked oscillator via a directional coupler.

I was not suggesting that ECC83 could be used at 2.4GHz, just that audio gain of 30dB is unremarkable. Maybe I misunderstood the "wow!" factor in the original post?
Wow (walk or wilt ) 500w at 2.4 ghz nasty stuff.
there is somwhere on the web a guy that built one of those magnatron RF amplifiers and then connected it to a 30 db parabolic dish if i remmember it only had a beamwidth of 8 degrees. WOW!!!!.
There is also an artical by the evil genius about constructing a device from a magnatron that will destroy your hifi from a moderate distance away . OK STOP WORRYING it will only harm your gear if it is switched on.
Regards Mad Mark
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Old 20th January 2011, 07:08 PM   #10
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Originally Posted by CivicProtection View Post
Folks, I found this document a number of years ago, skimmed though it then put it away on my HD. Dusted it off today, and here I am.
What is this? IS it really what it says it is?

http://72.52.208.92/~gbpprorg/mil/herf/magnetron_amplifier.pdf

It says 30db of gain. How can this be? Can this be a low noise audio amplifier or not? Any ideas?
Could you modulate it, rectify the output and filter out the RF, leaving a beautiful intact audio signal? Blindness may be an operating hazard...
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