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
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.
