Velocity factor of an insulated antenna wire.
 

First calculate P = Q / ( R + S )

where

Q = K * Ln( 4 * H / d )

R = K * Ln( 4 * H / D )

S = Ln( D / d )

and

K = permittivity of insulating material.

H = height of wire above ground.

D = Diameter over insulating material.

d = wire diameter.

All dimensions in same units.

Now P is the ratio of wire self-capacitance with insulation, to wire
self-capacitance without insulation. It follows that -

VF = Squaroot( 1 / P ) is the velocity factor along the insulated
wire.

With ordinary antenna wire insulated up to twice the wire diameter
with PVC, the reduction in velocity from the speed of light is
insignificant and pruning can be forgotten about. It is much less than
the pruning sometimes done for end effect which is usually unecessary
anyway.

To detect the effect precision measurements are necessary unless the
insulation has a diameter of several inches or more. For the
permittivity of the insulation to have full effect it would be
necessary to completely fill the infinity of space with the insulating
material.

Terman, Brown and Klaus all forgot to mention this in their bibles.
----
Reg, G4FGQ

On Fri, 1 Apr 2005 02:59:27 +0000 (UTC), "Reg Edwards"
wrote:

With ordinary antenna wire insulated up to twice the wire diameter
with PVC, the reduction in velocity from the speed of light is
insignificant and pruning can be forgotten about.
....
Terman, Brown and Klaus all forgot to mention this in their bibles.

Stands to reason doesn't it? They probably forgot to mention a lot of
inconsequential details like the impedance bumps of rivets in towers.

'Spose someone has to mention it, that's what newsgroups are for.

73's
Richard Clark, KB7QHC

The wire insulation they had in Ternman's day wasn't too good but expensive
so who in their right mind would use it for an antenna.

--

73
Hank WD5JFR
"Reg Edwards" wrote in message
...

First calculate P = Q / ( R + S )

where

Q = K * Ln( 4 * H / d )

R = K * Ln( 4 * H / D )

S = Ln( D / d )

and

K = permittivity of insulating material.

H = height of wire above ground.

D = Diameter over insulating material.

d = wire diameter.

All dimensions in same units.

Now P is the ratio of wire self-capacitance with insulation, to wire
self-capacitance without insulation. It follows that -

VF = Squaroot( 1 / P ) is the velocity factor along the insulated
wire.

With ordinary antenna wire insulated up to twice the wire diameter
with PVC, the reduction in velocity from the speed of light is
insignificant and pruning can be forgotten about. It is much less than
the pruning sometimes done for end effect which is usually unecessary
anyway.

To detect the effect precision measurements are necessary unless the
insulation has a diameter of several inches or more. For the
permittivity of the insulation to have full effect it would be
necessary to completely fill the infinity of space with the insulating
material.

Terman, Brown and Klaus all forgot to mention this in their bibles.
----
Reg, G4FGQ

Reg Edwards wrote:
First calculate P = Q / ( R + S )

where

Q = K * Ln( 4 * H / d )

R = K * Ln( 4 * H / D )

S = Ln( D / d )

and

K = permittivity of insulating material.

H = height of wire above ground.

D = Diameter over insulating material.

d = wire diameter.

All dimensions in same units.

Now P is the ratio of wire self-capacitance with insulation, to wire
self-capacitance without insulation. It follows that -

VF = Squaroot( 1 / P ) is the velocity factor along the insulated
wire.

With ordinary antenna wire insulated up to twice the wire diameter
with PVC, the reduction in velocity from the speed of light is
insignificant and pruning can be forgotten about. It is much less
than
the pruning sometimes done for end effect which is usually unecessary
anyway.

To detect the effect precision measurements are necessary unless the
insulation has a diameter of several inches or more. For the
permittivity of the insulation to have full effect it would be
necessary to completely fill the infinity of space with the
insulating
material.

Terman, Brown and Klaus all forgot to mention this in their bibles.
----
Reg, G4FGQ


If so where did all the entrenched bafflegab about antennas made from
insulated wire being shorter than antennas made from bare wire come
from??

w3rv

If so where did all the entrenched bafflegab about antennas made
from
insulated wire being shorter than antennas made from bare wire come
from??

w3rv

=========================

From old wives who built up an imaginary empire from something they
have erroniously gleaned from misquotations from the wrong magazines
and unthinking ragchews.

As occurs with masses of verbiage on other popular topics.

But it's all good fun and entertainment, is it not? ;o)
----
Reg.

The wire insulation they had in Ternman's day wasn't too good but
expensive
so who in their right mind would use it for an antenna.

--
The quality of insulation on antenna wires has absolutely no effect on
antenna performance. Even Terman knew that.

Reg Edwards wrote:
If so where did all the entrenched bafflegab about antennas made
from
insulated wire being shorter than antennas made from bare wire come
from??

w3rv

=========================

From old wives who built up an imaginary empire from something they
have erroniously gleaned from misquotations from the wrong magazines
and unthinking ragchews.

As occurs with masses of verbiage on other popular topics.

But it's all good fun and entertainment, is it not? ;o)

- - - - -

Humpf. I almost snookered myself into actually doing the experiments
discussed in the other thread.

.. . . grumble . . . !

I guess I'd be able to laugh at myself eventually.

I think I'll drop a line to MFJ and suggest that they develop an
Antenna BS Detector. Maybe as an accessory for their 259B analyzer.

- - - - -

----
Reg.

w3rv