On Tue, 28 Jun 2005 15:39:57 -0700, Frank Gilliland
wrote:

The energy in a coax travels on the conductors -and- in the dielectric
-and- within the magnetic fields. The propogation delay of a line is
the combined phase delays of distributed capacitance -and- distributed
inductance in the line. The dielectric constant only -seems- to be the
determining factor of coax propogation delay because the conductors
are straight. IOW, if you replace the center conductor with a coil you
will introduce an additional propogation delay into the coax which is
-independent- of the dielectric constant (and will have constructed a
device known to us old farts as a 'helical resonantor'). Regardless,
it has no relevance to this discussion.
*****

Well the dielectric constant does have a direct effect on the
capacitance as well as the spacing between the two conductors. Still
the TEM wave propogates through the dielectric and induces currents in
the center and outer conductor. Propogation of a TEM wave can be
mathematically describe by the Pyonting Vector. The TEM wave is an
alternating E and H field.

The currents induced into the conductors have depth only to that of
sigma or the skin depth. I am not sure a coiled center conductor would
introduce anymore delays than a solid or even stranded center
conductor. On face evidence it would seem that it might but only if
the coil's turns per inch were suffieciently low enough as to not
appear to the traveling wave as a solid conductor.

james

On Wed, 29 Jun 2005 16:17:33 GMT, james wrote
in :

On Tue, 28 Jun 2005 15:39:57 -0700, Frank Gilliland
wrote:

The energy in a coax travels on the conductors -and- in the dielectric
-and- within the magnetic fields. The propogation delay of a line is
the combined phase delays of distributed capacitance -and- distributed
inductance in the line. The dielectric constant only -seems- to be the
determining factor of coax propogation delay because the conductors
are straight. IOW, if you replace the center conductor with a coil you
will introduce an additional propogation delay into the coax which is
-independent- of the dielectric constant (and will have constructed a
device known to us old farts as a 'helical resonantor'). Regardless,
it has no relevance to this discussion.
*****

Well the dielectric constant does have a direct effect on the
capacitance as well as the spacing between the two conductors. Still
the TEM wave propogates through the dielectric and induces currents in
the center and outer conductor. Propogation of a TEM wave can be
mathematically describe by the Pyonting Vector. The TEM wave is an
alternating E and H field.


Well, let's put it this way: the radio and antenna don't connect to
the dielectric of a coax.


The currents induced into the conductors have depth only to that of
sigma or the skin depth. I am not sure a coiled center conductor would
introduce anymore delays than a solid or even stranded center
conductor. On face evidence it would seem that it might but only if
the coil's turns per inch were suffieciently low enough as to not
appear to the traveling wave as a solid conductor.


I'm sure you have studied the lumped-constant equivalent of a
transmission line.....






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On Wed, 29 Jun 2005 13:56:53 -0700, Frank Gilliland
wrote:

I'm sure you have studied the lumped-constant equivalent of a
transmission line.....
****

And Maxwell's equations

james

On Wed, 29 Jun 2005 13:56:53 -0700, Frank Gilliland
wrote:

Well, let's put it this way: the radio and antenna don't connect to
the dielectric of a coax.
*****

No it does not directly.

I know this concept is not easy to see but at the begining of the
coax, one can then consider the energy that travels down the coax as a
TEM wave. It is inside the dielectric where the E and H fields of the
traveling wave can be measured and found.

In transmission lines it is by far easier to think of E and H fields
within the the transmission line. Once that concept is mastered then
the rest is rather easy.

When the wave reaches the end, you have the final induced currents.
You can take a dipole and look at it as if the legs were an extension
of the transmission line. This can better be seen if you consider a
dipole and it is fed with open twin lead. The leads of the dipole then
are an extention of the twin lead except they are now at 90 degrees to
the transmission line.

Current is high when the magnetic field is high. This is so because
the induced current is controlled by the density of the magnetic
field. The E field is high when magnetic field is low. The E field
does not require current but voltage. On a center fed dipole the
impedance is low and the corresponding currents are high. The E field
off teh antenna is also low. As you progress a quarter wave from the
feed point in either direction the H field increases and the E field
decreases. With increasing H field the RF currents induced in the
antenna are high. Thus Ohm's law hald true. Z = I^2*R. Where R is the
radiation resistance of the antenna. The ends of a center fed dipole
are high impedance.

james