I thought I'd look up this subject and got nowhere. I didn't find it in
Kraus and some internet searching was futile.

As an example, if we have a transmitting dish that precisely covers a
receiving dish (and vice versa), such that there is no path loss. What
happens at the receiving dish with respect to re-radiated power?

That power is apparently sent back to the transmitter and then?

On 8/17/2015 4:04 PM, Wayne wrote:
I thought I'd look up this subject and got nowhere. I didn't find it in
Kraus and some internet searching was futile.

As an example, if we have a transmitting dish that precisely covers a
receiving dish (and vice versa), such that there is no path loss. What
happens at the receiving dish with respect to re-radiated power?

That power is apparently sent back to the transmitter and then?

Antennas For All Applications by John D. Krause and Ronald J. Marhefka,
3rd edition, ISBN 0-07-053243-5.

Page 29, immediately below equation 10:
"When the antenna is receiving with a load resistance Rl matched to the
antenna radiation resistance Rr(Rl=Rr), as much power is reradiated from
the antenna as is delivered to the load. This is the condition of
/maximum power transfer/ (antenna assumed lossless)."

They go on to say it applies to 1/2 wavelength dipoles but does not
apply to all antennas.

On Mon, 17 Aug 2015 14:04:07 -0700, "Wayne"
wrote:

I thought I'd look up this subject and got nowhere. I didn't find it in
Kraus and some internet searching was futile.

As an example, if we have a transmitting dish that precisely covers a
receiving dish (and vice versa), such that there is no path loss. What
happens at the receiving dish with respect to re-radiated power?

That power is apparently sent back to the transmitter and then?

It starts heating up the universe and we will all die.

Next question, please.

w.

Hi OM Wayne,

This setup works in spite of that!

http://nandustips.blogspot.in/2011/0...d-held-to.html

73,

Nandu.

"John S" wrote in message ...

On 8/17/2015 4:04 PM, Wayne wrote:
I thought I'd look up this subject and got nowhere. I didn't find it in
Kraus and some internet searching was futile.

As an example, if we have a transmitting dish that precisely covers a
receiving dish (and vice versa), such that there is no path loss. What
happens at the receiving dish with respect to re-radiated power?

That power is apparently sent back to the transmitter and then?

Antennas For All Applications by John D. Krause and Ronald J. Marhefka, 3rd
edition, ISBN 0-07-053243-5.

Page 29, immediately below equation 10:
"When the antenna is receiving with a load resistance Rl matched to the
antenna radiation resistance Rr(Rl=Rr), as much power is reradiated from
the antenna as is delivered to the load. This is the condition of /maximum
power transfer/ (antenna assumed lossless)."

They go on to say it applies to 1/2 wavelength dipoles but does not apply
to all antennas.

But, as in some other references I checked, the re-radiation is declared
rather than explained.

Way back in another life when I worked in the "black" world, we did some
mischief using reradiation.

Also, years ago in bug detection we hit locations with rf and looked for 3rd
harmonics generated by diode type junctions.
It worked pretty well, but we found a lot of bogeys, such as corroded wiring
connections.

On 8/18/2015 12:08 PM, Wayne wrote:


"John S" wrote in message ...

On 8/17/2015 4:04 PM, Wayne wrote:
I thought I'd look up this subject and got nowhere. I didn't find it in
Kraus and some internet searching was futile.

As an example, if we have a transmitting dish that precisely covers a
receiving dish (and vice versa), such that there is no path loss. What
happens at the receiving dish with respect to re-radiated power?

That power is apparently sent back to the transmitter and then?

Antennas For All Applications by John D. Krause and Ronald J.
Marhefka, 3rd edition, ISBN 0-07-053243-5.

Page 29, immediately below equation 10:
"When the antenna is receiving with a load resistance Rl matched to
the antenna radiation resistance Rr(Rl=Rr), as much power is
reradiated from the antenna as is delivered to the load. This is the
condition of /maximum power transfer/ (antenna assumed lossless)."

They go on to say it applies to 1/2 wavelength dipoles but does not
apply to all antennas.

But, as in some other references I checked, the re-radiation is declared
rather than explained.

Please explain the distinction. If you mean that the above is declared
without explanation then consider the following...

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.

I suggest you read the the book I referenced in my other post.

In addition, you might find this interesting
http://w4neq.com/htm/nist.htm

Scattering by the elements is something I can't address.

Way back in another life when I worked in the "black" world, we did some
mischief using reradiation.

Also, years ago in bug detection we hit locations with rf and looked for
3rd harmonics generated by diode type junctions.
It worked pretty well, but we found a lot of bogeys, such as corroded
wiring connections.

So, as you say, it was re-radiation since the source was 3 times higher
in frequency than the fundamental. I don't think scattering can do that.

Here's another antenna 're-radiation' application of mine.

http://nandustips.blogspot.in/2013/0...-repeater.html

73,

Nandu.

"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

"vu2nan" wrote in message
...
This setup works in spite of that!

http://tinyurl.com/cko3ypo

There is also the case of the magnetic loop (not so)close to a small BCL.

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.