On 2 Jan, 22:07, Mike Monett wrote:
* Keith Dysart wrote:

* [...]

* Notice a *key *point about this description. It *is *completely in
* terms of *charge. *There *is not a *single *mention *of *EM waves,
* travelling or otherwise.

* Now we expand the experiment by placing a pulse generator *at each
* end of *the *line and triggering them to each generate *a *50V one
* second pulse *at *the same time. So after one second *a *pulse has
* completely entered each end of the line and these pulse are racing
* towards each other at the speed of light (in the line). In another
* second these pulses will collide at the middle of the line.

* What will *happen? *Recall one of the *basics *about *charge: like
* charge repel. So it is no surprise that these two pulses of charge
* bounce off each and head back from where they came.

* [...]

* Keith

* Keith, your *model *is not realistic. As you *know, *any *signal you
* impose on a conductor will form an electromagnetic wave. This is the
* combination of *electrostatic *and *electromagnetic *fields, *and it
* propagates at the normal velocity for that medium.

* However, electromagnetic waves do not interact with each *other, and
* they cannot bounce off each other.

* Recall that *light *from stars is *electromagnetic. *It *travels many
* light-years before *it reaches your eyes. *If *electromagnetic waves
* interacted, you *would *not be able to see individual *stars *- they
* would merge into a blur.

* Similarly, the signals reaching your antenna and traveling *down the
* coax to *your receiver do not interact with each other. *As *long as
* your receiver *is *not overloaded, the *signals *remain *separate no
* matter how many stations are on the air at the moment.

* So the *statement *that *like * charges * repel *does *not *apply to
* electromagnetic waves, and the pulses cannot bounce off each other.

* Regards,

* Mike Monett

Mike
They will not listen to you because they are following books that are
incorrect.
They cannot get into their minds that for a given frequency the time
for
a cycle is always the same. And as I have pointed out many times in
different ways
that goes for 1/2 wave antennas too.
If one bends a half wave antenna such that the ends are close together
you
can feed at the wire ends.
So now you apply a DC current at one end and it will continue to go
forward
all the way to the other end of the wire.Wen it gets to the end of the
wire
the current reverses direction and goes back to the starting point
which
completes one wave length of travel which also represents one
wavelength of time.
Now the other side of the debate wants a half wave antenna.So let us
lay
that half wave antenna out in a similar way that we bent the half wave
length
antenna
Start a DC current at one end and it travels to the other end of the
wire
BUT TIME HAS NOT RUN OUT FOR FLOW IN THE SAME DIRECTION,and this is
the
crux of the debate since the current still has to move forward and
thus
can only procede down the center of the wire .
IT CANNOT GO BACK AT THIS TIME.
The time for forward travel runs out when it gets to the end of the
wire.
When time runs out it reverses direction and goes back up the inside
of
the wire and down the outside of the wire to the end or shall we say
return to the beginning to complete the cycle.
It can be seen that with a half wave antenna the current flows on the
surface
only half of the time such that it only encounters inductance and
capacitance
for half of a cycle such that it can radiate. The rest of the time
because
the current flow is not exposed to the surface it does not radiate.
At no time is the current going two different ways.
Unfortunately people ignore the requirements of time and for some
reason want to change current direction to half the time required
for that frequency thus creating collisions in the current flow.
THIS DOES NOT HAPPEN. So gentlemen layout a bent full wave
antenna and along side it lay out a half wave antenna in the same
fashion and start current flow in both at the same time where
length of travel is commensurate with time. You will now realise
that all participants in this debate have been talking past each
other.
Another way of looking at it is to draw a full wave length of
communicationline in ladder form with its component inductances
and capacitances. One side of the ladder drawn line has zero
energy storage components only resistance and it is this
line that represents travel down the center of the wire.
The bottom line is that a half wavelength antenna represents
a full cycle with respect to frequency.
This will be the last time that I will try to explain the radiation
characteristics of a antenna.
Best regards to all
Art Unwin KB9MZ.....XG