"David" wrote in message
...
OK, so the electrical wavelength of the tube will only be effected
by
the dielectric material and it does not make any difference how
large
the gap is between the Sleeve and the Coax ?

The frequency of operation is 920 MHz.

Do you happen to know what the covering is made of on the outer
sheath
of RG174 ?
=======================================

The jacket of coaxial cable is usually a soft grade of
poly-vynil-chloride, PVC, which can have a dielectric constant
anywhere between 4 and 6.

The velocity factor along the outside of the coaxial braid depends on
the thickness of the jacket. To make much difference to the VF it has
to be an inch thick or more whereas it is probably only about 0.6mm.

I will have a guess and say the VF is about 0.95. You can forget
about it.
----
Reg.