how rf leave the antenna
 

If an rf source is applied at the A end of the length of wire from A
to B, the wave will travel along the wire until it reaches the B end.
Since the B end is free, an open circuit exists and the wave cannot
travel . This is a point of high impedance. Then the wave back
(reflects) from this point of high impedance and travels toward the
starting point, where it is again reflected. The energy of the wave
would be gradually dissipated by the resistance of the wire of this
back-and-forth motion (oscillation);


rf source A .____wire____.B


So how rf leave the antenna ???!!!!!!

in practical we use this configration :


---------- Antenna
rf source (transmmiter) ----|
---------- dummy load

Thanks

Best look at URL:
http://www.people.fas.harvard.edu/~t...rticle_EDN.pdf


"dado" wrote in message
om...
If an rf source is applied at the A end of the length of wire from A
to B, the wave will travel along the wire until it reaches the B end.
Since the B end is free, an open circuit exists and the wave cannot
travel . This is a point of high impedance. Then the wave back
(reflects) from this point of high impedance and travels toward the
starting point, where it is again reflected. The energy of the wave
would be gradually dissipated by the resistance of the wire of this
back-and-forth motion (oscillation);


rf source A .____wire____.B


So how rf leave the antenna ???!!!!!!

in practical we use this configration :


---------- Antenna
rf source (transmmiter) ----|
---------- dummy load

Thanks

George Micheal wrote:
"So how rf leave the antenna?"

The end-fed wire antenna is a circuit completed by capacitance to ground
and its return to the transmitter.

In a good antenna system, only a small percentage of the total r-f is
lost in wire, ground, feedline, etc. Nearly all is radiated.

A current-carrying wire is surrounded by magnetic lines of force as
exhibited by solenoid magnets, motors, etc.

An electrically charged item radiates an electric force field as
exhibited by an Ace comb`s attraction for bits of paper under the right
conditions.

A varying magnetic field can induce an electrical potential in a wire.
It happens in common electrical generators. Likewise a varying electric
field can alternatly attract and repel electrons, thereby producing an
slectric current capability.

R-F circulating in the antenna wire produces alternating magnetic
(H)-fields and electric (E)-fields around the wire.

The question is what impels these fields to travel to much greater
distances than static fields travel. J. C. Maxwell speculated that
displacement current of the sort that flows through the dielectric of a
capacitor is surrounded by magnetic flux the same as current through a
wire is. He was right.

Displacement current requires no electron flow. Note that we have vacuum
capacitors where the space between the plates is completely void.

Displacement current makes the radio wave self-perpetuating. An H-field
out in space creates an E-field by generating a "potential difference"
which produces a "displacement current" which in turn generates a
"potential difference" as represented by the E-field, which generates a
"displacement current" as represented by the H-field.

This back and forth energy swap between E&H fields just goes on and on.

Best regards, Richard Harrison, KB5WZI