"John S" wrote in message
...
On 8/18/2015 12:08 PM, Wayne wrote:


An rf signal hits the antenna and becomes a generator with a source
impedance in the element. As a result, some current flows into the load.
The current that flows into the load also flows in the source and its
impedance. If you have a current in the source's impedance (the antenna),
it must radiate due to that current. If you have no load, there will be no
re-radiation.

Yes it seems to work as at DC:
If you have a generator of R0 internal resistance to get maximum
power from it you must load it with an R0 load.
And the power you get is the same as the one lost in the generator.

At RF it becomes tricky:
A matched dipole in that case re-radiates half the power involved......OK
If shorted I understand it re-radiates all....still OK with me
But if left open it is just 2 quarter wave end to end.
It should re-radiate very little at F0 and a lot at 2 F0
Now if the dipole is connected to an open or shorted transmission line
I leave it to you :-)
73's

On 8/19/2015 1:59 PM, bilou wrote:
"John S" wrote in message
...
On 8/18/2015 12:08 PM, Wayne wrote:


An rf signal hits the antenna and becomes a generator with a source
impedance in the element. As a result, some current flows into the load.
The current that flows into the load also flows in the source and its
impedance. If you have a current in the source's impedance (the antenna),
it must radiate due to that current. If you have no load, there will be no
re-radiation.

Yes it seems to work as at DC:
If you have a generator of R0 internal resistance to get maximum
power from it you must load it with an R0 load.
And the power you get is the same as the one lost in the generator.

At RF it becomes tricky:
A matched dipole in that case re-radiates half the power involved......OK
If shorted I understand it re-radiates all....still OK with me
But if left open it is just 2 quarter wave end to end.
It should re-radiate very little at F0 and a lot at 2 F0
Now if the dipole is connected to an open or shorted transmission line
I leave it to you :-)
73's

No, the two halves cannot change the frequency of the incoming signal.
However they will probably do some scattering similar to a flag pole or
the side of a barn or some such.