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How did they communicat ?

Discussion in 'Electronic Basics' started by John Popelish, Apr 1, 2007.

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  1. All frequencies of radio waves travel, without loss, through
    the vacuum of space. But the atmosphere traps some bands of
    frequency in a waveguide effect, near the surface of
    Earth. Those frequencies allow long distance communication
    around the curvature of Earth, but are poor choices for
    communication between surface and space. But even these
    frequencies leak out into space, to some extent, especially
    when launched near the vertical. Here is a paper that goes
    into more detail:
    http://www.ips.gov.au/Category/Educational/Other Topics/Radio Communication/Intro to HF Radio.pdf

    But there are lots of frequency choices that are not
    reflected much by the atmosphere, but travel essentially in
    a straight path through it into space, and back from space.
     
  2. mowhoong

    mowhoong Guest

    During my school days about 35 years ago, we were taught in our
    physics lessons, the radio wave only travels or reflect in our
    atmosphere when we listen to FM/AM ,CV band, Air band boardcast. But
    I am curious to know how the radio wave communicate to the satellite
    as air
    do not even exist in space, this is just like vacuum space. Can any
    kind soul out there explain? Thank you very much.
    Regards
     

  3. All waveforms from the bottom of the radio frequency spectrum and above
    can travel effortlessly through the vacuum of space. Some are however
    reflected off the Ionosphere (LW-MW-HF) or ducted through the Troposphere
    (VHF) but still largely manage to make it into space.--
    #1 Offishul Ruiner of Usenet, March 2007
    #1 Usenet Asshole, March 2007
    #1 Bartlo Pset, March 13-24 2007
    #10 Most hated Usenetizen of all time
    Pierre Salinger Memorial Hook, Line & Sinker, June 2004
    COOSN-266-06-25794
     
  4. Ether is dead ... gone ... kaput ... killed by Einstein and others ... April
    Fool!
     

  5. Be kind, Charles, Some of them are fools all year long.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  6. feebo

    feebo Guest

    The radio transmission does not rely on the oscillation of the air in
    the same way sound does.

    If it helps to get your head round the idea, think of it along the
    following lines...

    radio waves are electro-magnetic.

    ask yourself - "do magnets work in a vacuum?"

    In the vacuum of space, radio energy travels quite effectively - it
    does lose energy over distance but the losses are much smaller than in
    air etc.

    remember those experiments you did with a bit of wire going through
    some paper, pass a current through the wire and sprinkle iron filings
    on the paper to see the lines of magnetic flux around the wire? Think
    of radio waves as the lines of filings and think of the antenna as a
    wire cutting the lines of flux (and so inducing a voltage - generator
    theory) - this is not precisely how it works but the illustration is
    good for now.

    radio waves pass through any medium with varying losses... some media
    have little effect, others will stop them dead in their tracks. It's
    not just down to the substance of the media either, it could be it's
    electrical properties or construction or a mixture - google "faraday
    cage"

    Now, think back to audio for a second (as your initial question seemed
    to centre on oscillations of the air)... when some kid in his car goes
    past with the stereo wound right up, all you hear is the bass, right?
    Very generally, the higher the frequency, the shorter the distance of
    effective transmission through a medium. Low frequencies penetrate the
    walls of the vehicle (and the air) better than the high frequencies...

    whale-song is very low frequency and travels for miles through the
    oceans... elephants use growls of <20Hz to communicate between herds
    that may be miles apart on the savanna.

    Submarines also use ULF when submerged and their radio signals travel
    right round the globe. A listening station not far from me was used
    during the cold-war to co-ordinate submarine fleets thousands of miles
    away. Problem with ULF is the data-rate is very low - messages take a
    relatively long time to transmit and recieve, so submarines prefer to
    surface to communicate with normal frequency radio - usually at
    pre-arranged times.
     
  7. mowhoong

    mowhoong Guest

    Thanks to all members who responsed to my posting.
    Best Regards
     
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