"Reg Edwards" wrote

To calculate change in velocity due to plastic PVC insulation we
need
to know :-

Wire diameter = d
Diameter over insulation = D
Height of wire above ground = H
Permittivity of insulating material = K

First calculate capacitance of bare wire to ground.
Then calculate capacitance of insulated wire to ground.
Velocity Factor = SquareRoot of their ratio.
Neither Terman's nor Kraus' Bibles will mention the following
formulae. So you'll just have to take my word for it.


Velocity Factor = SquareRoot( ( A + B ) / C )

Where -

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

B = Ln( D / d )

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

Example :
Bare wire diameter = 1.6 mm = 14 awg.
Diameter over insulation = 2.6 mm.
Height above ground = 10 metres = 33 feet.
Permittivity of insulation = 3.5

Velocity factor = 0.983
Or a decrease in resonant frequency of 1.7 percent which can nearly
always be forgotten about.

The electrical effect of the enamel on magnet wire is entirely
negligible. But it does protect the wire from atmospheric pollution.

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

After a couple of days, and the time it took to derive the equations,
does nobody want to argue about it ? What about you, my dear Richard
Clark ?

By the way, I have now reverted to Australian, Banrock Station red
plonk as being the best buy in my local supermarket. To get into my
glass it has to come 12,000 miles. But, like it or not, our small
globe gets smaller day by day.
----
Reg, G4FGQ.