Where is it ?  Look at the Sky, its every where

But I can't see anything.   Fooled you,
It's invisible, but not to Spy transmitter Radio Waves

What does the ionosphere do. It bends radio signals back
 to earth , otherwise they would just shoot off into space.

Click the picture of the two WW2 Spy's to see how they are
 using the Ionosphere to communicate.

They are using the reflected wave, not the ground wave
 as they are too far from England.

How do the radio waves get reflected? Radio waves are
 just like light, they can be reflected as light is on a mirror
 or like light, diffracted through glass.
 
The Ionosphere is made up of billons of charged particles 
in the atmosphere which the radio waves can't pass
 through, so they gradually bend back to earth.

Is the Ionosphere just a single layer? 
No it's really complex having many layers which are
 constantly changing, so you can never guarantee your Spy
 signal will always be reflected to get back to England. 

What makes the Ionosphere change its reflections?  
It's many things, The time of day, The day in the month,
 The season, The weather in space, The radio frequency
 and Over a 11 year cycle, how many spots the sun has. 
Yes the Sun really does have Spots,  
never look directly at the Sun,
 best to "Click Here"  WOW they are Big Spots!

Can Spy signals travel further than England? 
Yes for long distances, radio waves have to bounce off 
the Ionosphere and then the ground several times, to
 reach countries like Australia. (Much like a bouncing ball)

Until to a few years ago, the only way of sending radio
 signals all around the world, was by the Ionosphere,
 But now, Spy's radio signals are reflected by satellites
 orbiting the earth above the Ionosphere.

Why doesn't the Ionosphere reflect the signal going to the
 Satellites?
The satellites use UHF, "Ultra High Frequency Waves"
 which are far too short to be reflected by the Ionosphere.
 Except for solar storms, satellite signals are not effected
 in the same way Ionosphere, increasing reliability.

What happens to radio signals that pass through the
 Ionosphere?
Nothingthey just keep going for ever, getting very slightly
 weaker for each Kilometer.
This means an Alien can listen to all our TV and Radio,
  since 1920's. If they were  100,000,000 Km away they
 may be listing to signals Spy's had sent in WW2. as the
 signal from the 1940's would only have just reached them.

How do we use Radio Waves Today
Radio waves today dominate our lives, but because they
 are invisible, we have no idea they are all around us.
 This very moment waves are hitting your body,
they may have been sent from the other side of the earth.

Can you guess how we use radio waves today?
     "Click Here for some of My Answers "