skin depth decay
 

On 20 Nov, 08:47, (Richard Harrison) wrote:
Art wrote:

"Richard can be excused for making this error."

Prove I erred!

Roy pointed it out not I. He can be more specific
to what he was pointing out. I have no wish to explain
on his behalf




Put a sine wave in an antenna and you get a sine wave out.

Very true

Kraus says:
"The currents on the transmission line flow out on the antenna and end
there, but the fields associated with them keep on going."

Could be


Art in a previous posting said I should quote "Lady Chatterley`s Lover"
as people were tiring of Terman. I read it before it was even printed in
the U.K. (1960) but this is an antenna newsgroup and Terman is more
appropriate.

But I have never read it!

I don't believe I pointed to " Maxwell" but all of the scientists
involved with radiation, and there are many. I didn't make a point
of searching for the names just don't recall seeing them.


If people want something other than Terman, he gives a terrific
bibliography at the bottom of page 864 in his 1955 opus.

I will take a look at that


Art also said in a previous posting that Terman did not credit Maxwell
with defining radiation. Let me put the lie to that.
On page 864 of his1955 opus, Terman writes:

"The laws governing such radiation are obtained by using Maxwell`s
equations to express the fields associated with the wire; when this is
done there is found to be a component, termed the radiated field having
a strength that varies inversely with the distance."

Best regards, Richard Harrison, KB5WZI
Have a happy harvest festival, the name assigned
before the Americans changed the name. I woinder when
the word "thanksgiving" came into being?

skin depth decay
 

Richard Harrison wrote:
Kraus says:
"The currents on the transmission line flow out on the antenna and end
there, but the fields associated with them keep on going."

Actually, in a standing-wave antenna, such as a 1/2WL dipole,
the antenna wave currents bounce back and forth between the
open ends and the feedpoint. If there is not a Z0-match to the
feedline at the feedpoint, some of the antenna current reflected
from the open end of the antenna leaks back into the feedline and
makes it's way back to the source. A TDR will register reflections
both from the feedpoint and the open ends of the antenna.
--
73, Cecil http://www.w5dxp.com

Thanksgiving
 

art wrote:

Have a happy harvest festival, the name assigned
before the Americans changed the name. I wonder when
the word "thanksgiving" came into being?

http://showcase.netins.net/web/creat...hes/thanks.htm

73, jk

skin depth decay
 

On 20 Nov, 10:58, Cecil Moore wrote:
Richard Harrison wrote:
Kraus says:
"The currents on the transmission line flow out on the antenna and end
there, but the fields associated with them keep on going."

Actually, in a standing-wave antenna, such as a 1/2WL dipole,
the antenna wave currents bounce back and forth between the
open ends and the feedpoint. If there is not a Z0-match to the
feedline at the feedpoint, some of the antenna current reflected
from the open end of the antenna leaks back into the feedline and
makes it's way back to the source. A TDR will register reflections
both from the feedpoint and the open ends of the antenna.
--
73, Cecil http://www.w5dxp.com

An antenna I played with years ago was a sample of this search
by current flow. It was a dipole where the center was a closed
loop.The low current curve stated at the end of the dipole
and moves to the loop where it will circulate
until the match is right for it to travel on to the other end
of the dipole to achieve a low current point which is required
for resonance.
The machanical analogy of this is a mechanical rotary
pump where it deals with shear and cavitation of water flow.
But I don't think that is what Roy was alluding to as much
as it was a failure of understanding with respect to current
and voltage phase.
But I will have to wait and see what Roy meant.
Regards
Art Unwin KB9MZ....XG

Thanksgiving
 

Jim Kelley supplied the URL of Lincoln`s Thanksgiving Day proclamation
during the American Civil War. It goes back much before Lincoln.

Thanksgiving predates the joint celebration of English colonists and
American Indians at Plymouth in 1621. Thanksgiving gatherings have
occurred throughout the world and throughout history. In America, the
natives traditionally had several of these festivals a year long before
the Europeans arrived. The English colonists did not call the 1621 event
a "thanksgiving". They actually had their first thanksgiving in the
summer of 1623 for rain which ended a long drought.

Happy Thabksgiving!

Best regards, Richard Harrison, KB5WZI

skin depth decay
 

Cecil, W5DXP wrote:
"A TDR will register reflections both from the feedpoint and the open
ends of the antennas."

Why reflections from the feedpoint if the antenna matches the feedline?

Best regards, Richard Harrison, KB5WZI

Thanksgiving
 

On 20 Nov, 12:34, Jim Kelley wrote:
art wrote:
Have a happy harvest festival, the name assigned
before the Americans changed the name. I wonder when
the word "thanksgiving" came into being?

http://showcase.netins.net/web/creat...hes/thanks.htm

73, jk

Interesting. My first observance of Harvest festival when my church
had products that had been harvested from the earth on every surface
that was flat. These products were given to the poor who lived rent
free
on grounds owned by the church. At the same time King George dished
out
special coins known as "Maunday" money since he was head of the
Church of England
courtesy of Henry VIII.Since it was puritans that first settled in
America
I suspect that the church function was also connected to the Catholic
church
heritage. Looks like Lincoln rolled it into one celebration after the
Civil War
tho it is suggestive that the church holiday was in position before
then
but with the name unknown.
Thanks JK
Art

skin depth decay
 

Richard Harrison wrote:
Cecil, W5DXP wrote:
"A TDR will register reflections both from the feedpoint and the open
ends of the antennas."

Why reflections from the feedpoint if the antenna matches the feedline?

If the antenna is fed with 50 ohm coax, the antenna
does not match the feedline. The Z0 of a #14 wire
30 feet in the air is ~600 ohms. It takes a half-cycle
of sinusoidal RF for the feedpoint impedance to begin
to match the coax Z0, i.e. the feedpoint impedance of
a standing wave dipole is a virtual impedance that
doesn't exist until the first reflections arrive from
the ends of the antenna.

Before Reg died, he had something to say about that.
--
73, Cecil http://www.w5dxp.com

skin depth decay
 

I wrote:
"The impressed current will lag the voltage across a pure inductance by
90 degrees."

Roy wrote:
"For other waveforms (like the ones you`d get connecting batteries or
capacitors) you have to resort to the more general time relationship
L*di/dt.

Roy is correct for connecting batteries or capacitors but Art was
working wih a lengthy antenna, not a lone elementary segment. He also
had no step functions, just a sine wave driving his antenna.

Best regards, Richard Harrison, KB5WZI

skin depth decay
 

Cecil, W5DXP wrote:
"If the antenna is fed with 50 ohm coax, the antenna does not match the
feedline."

I get the picture. everal iterations are needed to reach a match. But,
it all happens so fast there is little practical significance.

Best regards, Tichard Harrison, KB5WZI