Can an aimed Magnetron radiate into space ?

Sinedup · Jul 23, 2018

While working on my microwave recently, a thought popped in my mind.
Will a 2.45GHz 1.5KW Magnetron beam into space?
While it's illegal to broadcast certain RF frequencies without certification, would a standard microwave magnetron, no extra waveguides / dishes etc, pointed directly up, at the zenith, obviously on a raised wooden platform way above heads, transmit any distance?
Normally, running an empty micro oven will destroy the magnetron, if it doesn't have a load (water molecules), as is always warned in manuals.
I've also read on micro-repair websites that the u-wave energy reflections bounce back into the waveguide antenna, which causes the damage.
This is why I'm curious whether 'out in the open' atmosphere 'no-load' would also damage the magnetron?
(Obviously with cooling & HT still in operation, ie a micro oven with 'oven' section cut off.
A radio communications / circuit theory handbook states that the transmission window (through atmospheric layers to space) is from 20m (15 MHz) to 6mm (50 GHz), and the 2450 MHz falls well within this range.
However, the 1500-2000W power-to-distance is unknown.
Any theoretical wizards know the answer(s)?
Just curious..

dknguyen · Jul 23, 2018

Sinedup said:
While working on my microwave recently, a thought popped in my mind.
Will a 2.45GHz 1.5KW Magnetron beam into space?
While it's illegal to broadcast certain RF frequencies without certification, would a standard microwave magnetron, no extra waveguides / dishes etc, pointed directly up, at the zenith, obviously on a raised wooden platform way above heads, transmit any distance?
Normally, running an empty micro oven will destroy the magnetron, if it doesn't have a load (water molecules), as is always warned in manuals.
I've also read on micro-repair websites that the u-wave energy reflections bounce back into the waveguide antenna, which causes the damage.
This is why I'm curious whether 'out in the open' atmosphere 'no-load' would also damage the magnetron?
(Obviously with cooling & HT still in operation, ie a micro oven with 'oven' section cut off.
A radio communications / circuit theory handbook states that the transmission window (through atmospheric layers to space) is from 20m (15 MHz) to 6mm (50 GHz), and the 2450 MHz falls well within this range.
However, the 1500-2000W power-to-distance is unknown.
Any theoretical wizards know the answer(s)?
Just curious..

According to this:

https://space.stackexchange.com/que...wer-does-dsn-need-to-send-commands-to-voyager
There is an antenna that communicates with a satellite at the L1 Lagrange point (1.5 million km) that transmits on 2.1 GHz at 1.8kW

BTW, you don't need a license to transmit on 2.4GHz, but you are legally limited in how much power you can use.

Sinedup · Jul 23, 2018

Very interesting and informative, thank you.

ronsimpson · Jul 23, 2018

Sinedup said:
Will a 2.45GHz 1.5KW Magnetron beam into space?

Micro wave ovens work because water adsorbs energy at 2.45ghz.
The FCC did not regulate the 2.45 band (much) because they though no one would try to communicate at 2.45.
Indoors, wireless networks work because the air is try. Out doors it is not so good. Any time it rains or fogs I loose my outdoors links. I moved over to 5ghz and do not have problems now.

k7elp60 · Aug 8, 2018

A long time a go I used to work on surface search radar. The transmitting frequency was about 10GHz. The peak power was about 50KW, that was pulsed, I don't remember the pulse width or the time between pulses. The antenna was a semicircle and the range was in excess of 50 nautical miles. It used a Magnetron as a transmitter and a klystron as a receiver local oscillator and a diode mixer for the receiver det. As I recall the IF frequency was 30Mhz. At the operating frequency wave guide was the transmission line.

crutschow · Aug 9, 2018

It won't go very far without an an appropriate antenna at the end of the waveguide.
With no antenna, the wavefront would disperse at a wide angle, thus the beam power density would rapidly drop to the point where it couldn't be detected.
Edit: Also I think a fair amount of energy will be reflected back to the magnetron by the large impedance discontinuity between the waveguide and the air.
A proper antenna provides an impedance match between the waveguide and space.

atferrari · Aug 9, 2018

k7elp60 said:
A long time a go I used to work on surface search radar. The transmitting frequency was about 10GHz. The peak power was about 50KW, that was pulsed, I don't remember the pulse width or the time between pulses. The antenna was a semicircle and the range was in excess of 50 nautical miles. It used a Magnetron as a transmitter and a klystron as a receiver local oscillator and a diode mixer for the receiver det. As I recall the IF frequency was 30Mhz. At the operating frequency wave guide was the transmission line.

And the outcome was?

k7elp60 · Aug 11, 2018

atferrari said:
And the outcome was?

It was a radar aboard a ship and was used to detect other ships or land near the sea.

Nigel Goodwin · Aug 11, 2018

k7elp60 said:
It was a radar aboard a ship and was used to detect other ships or land near the sea.

But surely used an 'antenna' anyway? - usually a dish for radar.

k7elp60 · Aug 11, 2018

Nigel Goodwin said:
But surely used an 'antenna' anyway? - usually a dish for radar.

Nigel you are right, I could not remember the name for the radar antenna, it wan't a full dish.

k7elp60 · Aug 11, 2018

Nigel Goodwin said:
But surely used an 'antenna' anyway? - usually a dish for radar.

I think it was a Parabolic Reflector antenna.

Nigel Goodwin · Aug 12, 2018

k7elp60 said:
I think it was a Parabolic Reflector antenna.

Sounds right, a very high gain antenna - as you see spinning round on ships

k7elp60 · Aug 12, 2018

Nigel Goodwin said:
Sounds right, a very high gain antenna - as you see spinning round on ships

It was on a number of US Coast Guard Cutters. I was stationed on 3 of them in the early 1960's

unclejed613 · Aug 18, 2018

you will need a waveguide and at the very least a horn antenna. the horn shape is an impedance matching section between the waveguide and free air. you would be hard pressed to actually be able to communicate with a satellite, because of the amount of moisture in the atmosphere would cause huge losses, and the fact that the satellite is not communicating on 2.4Ghz, but on 2.1Ghz. magnetrons aren't tunable devices because the cavities inside the magnetron are a fixed size. there may be a certain amount of voltage tuning that can be done, but you're not going to be able to wobble the magnetron's frequency enough to get to 2.1Ghz. there are amateur radio operators that have used oven magnetrons for EME communication, but that's because the lower portion of the ISM band overlaps an amateur radio band. you would need to be a licensed ham to operate the magnetron as a transmitter for communications.

JMW · Dec 6, 2018

k7elp60 said:
Nigel you are right, I could not remember the name for the radar antenna, it wan't a full dish.

What RADAR? I started on SPS 6 and 10. The 6 was Air search. 10 gigs is X band. S band is around 3-4. X has better resolution, but rain and heavy fog hurt it. IIRC the 10 had a closed array, while the 6 was very large. Both were parabolic. Go to a marine store and look at the new RADAR, stuff we only dreamed about in the 60's.

JMW · Dec 6, 2018

k7elp60 said:
It was on a number of US Coast Guard Cutters. I was stationed on 3 of them in the early 1960's

So was I, Southwind WAGB 280. 70-72. Got reactivated after 9/11. Signed a 4 yr contract, Did 3.5 yrs on a 270 out of K.W.

unclejed613 · Dec 6, 2018

at Ft Campbell we had a radar test set brought into the calibration lab for repair. the complaint was "PPI, IFF, PRF test functions are ok, does not work in OFF mode"

JMW · Dec 6, 2018

unclejed613 said:
at Ft Campbell we had a radar test set brought into the calibration lab for repair. the complaint was "PPI, IFF, PRF test functions are ok, does not work in OFF mode"

Marine???

debe · Dec 8, 2018

This is a typical small marine radar Koden 32Nm 5Kw radar. The antenna is a Slotted Waveguide, the longer the antenna the narrower the beam.

unclejed613 · Dec 11, 2018

JMW said:
Marine???

Army.... butterbar (2nd lieutenant)... i wouldn't be surprised if it happens a lot as a prank, trolling the "new guy". just like we would send newbies to the motor pool or radio shop for a box of grid squares and compass bearings.

interesting that everything in that picture is smaller than i would have expected... the data sheet (for an MG4004 which is a replacement for the 9M302) specifies the peak power as 4kW, with pulses of 1uS at a rate of 1khz PRR. average power according to the data sheet is about 4W at a duty cycle of 0.001. i found the data sheet from a chart on this page https://www.aepmarineparts.com/products/e2v-radar-components/magnetrons/gen4-magnetrons/ showing that the 9M302 and MG4004 are equivalent, and the data sheet is here: https://www.aepmarineparts.com/wp-content/uploads/2016/09/MG4004.pdf

EDIT: according to Murphy's Laws of Combat, there's nothing more dangerous than a second lieutenant with a map and compass.

Can an aimed Magnetron radiate into space ?

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