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Can an aimed Magnetron radiate into space ?

Discussion in 'Radio and Communications' started by Sinedup, Jul 23, 2018.

  1. Sinedup

    Sinedup Member

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    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.. :D
     
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  2. dknguyen

    dknguyen Well-Known Member

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    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.
     
    Last edited: Jul 23, 2018
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  3. Sinedup

    Sinedup Member

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    Very interesting and informative, thank you.
     
  4. dave miyares

    Dave New Member

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  5. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    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.
     
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  6. k7elp60

    k7elp60 Active Member

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    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.
     
  7. crutschow

    crutschow Well-Known Member Most Helpful Member

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    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.
     
    Last edited: Aug 11, 2018 at 2:57 PM
  8. dave miyares

    Dave New Member

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  9. atferrari

    atferrari Well-Known Member

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    And the outcome was?
     
  10. k7elp60

    k7elp60 Active Member

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

    Nigel Goodwin Super Moderator Most Helpful Member

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    But surely used an 'antenna' anyway? - usually a dish for radar.
     
  12. k7elp60

    k7elp60 Active Member

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

    k7elp60 Active Member

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    I think it was a Parabolic Reflector antenna.
     
  14. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Sounds right, a very high gain antenna - as you see spinning round on ships :D
     
  15. k7elp60

    k7elp60 Active Member

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

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