# Try telling me this

## Main Question or Discussion Point

Hey there everybody.

I have a question which till date no professor has been able to answer. At least as far as I know.
Its a basic antenna question.

We all know that any moving charged particle generates EM waves. That is how an antenna works, when the electrons on the antenna are excited at a particular freq, they generate EM waves of that freq. That travels to a recieving antenna and induces oscillations of the electrons in THAT antenna at the same freq. My question is:
How does the recieving antenna convert the oscillations of the electrons to current? There is no transfer of electrons from the transmitting antenna to the recieving one, only EM radiation. And the electrons from the antenna are not fed into the circuits which drive a radio or LEDs which light up when EM waves strike it, like the stickers you stick on your cell phones, and which light up when ever you make or recieve a call.

This site might make it clear if Ive confused you
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=7566

But it talks only about the transmitting side. My question is on the recieving side.
I really appreciate it if anyone could hlpe me out.
Thanks a lot.

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vanesch
Staff Emeritus
Gold Member
My question is:
How does the recieving antenna convert the oscillations of the electrons to current?
What do you think a current is ?

Gold Member
Antenna gives off radio waves. Radio waves = EM wave = Photon = Energy (E = hf). The energy from the photon is given to a electron in the other antenna creating current.

clem
In a conducting rod antenna, the E field of the EM wave creates an AC EMF in the rod.
In a loop antenna, the B field of the EM wave creates a changing flux through the loop,
giving an EMF by Faraday's law.

Thanks for the replies guys.
@ Clem,
How is the AC EMF fed to the circuitry of the reciever once it passes thru the antenna stage?
Is there a terminal EMF or something which is created at the feedline of the antenna? After that how does it get into the circuit?
I know very well that the current (i.e movement of electrons) which flows into the amplifier modules of your standard radio, does NOT come from the recieving antenna.

Thanks

clem
The antenna just acts like an AC generator in the circuit.

berkeman
Mentor
I know very well that the current (i.e movement of electrons) which flows into the amplifier modules of your standard radio, does NOT come from the recieving antenna.
Of course it does. This is an AC current at the RF carrier wave frequency, so the electrons in the antenna and coax cable and input to the receiver amp are all oscillating at the RF carrier wave frequency. The electrons in the metal antenna are experiencing the periodic force from the EM wave going by, and that force is what causes the motion of those electrons, which causes the propagation of the wave (AC motion of the electrons) in the coax cable connected between the antenna and the receive amp input.

Then how is the circuit completed?
Cos the circuit is grounded. And im pretty much sure there is no depletion of electrons.
the electrons cant be replenished from the air, cos antenna works in space also!!!!!!

russ_watters
Mentor
Then how is the circuit completed?
Cos the circuit is grounded. And im pretty much sure there is no depletion of electrons.
the electrons cant be replenished from the air, cos antenna works in space also!!!!!!
It's AC! There is no "depletion of electrons".

I know im asking a really dumb question. But can you please explain how electrons move in an Alternating Current through a circuit?

russ_watters
Mentor
They literally just move back and forth in the wire.