Just need to get these things clarified!

The velocity factor of a tx line is governed by its distributed
inductance and capacitance, is it not?
I mean the more L and C you have per meter of line the lower the
signal velocity, right?
How much is the signal speed retarded by typically and are there any
circumstances where we need to be concerned about this phenomenon?

phaedrus wrote:
Just need to get these things clarified!

The velocity factor of a tx line is governed by its distributed
inductance and capacitance, is it not?

Yes.

I mean the more L and C you have per meter of line the lower the
signal velocity, right?

Right.

How much is the signal speed retarded by typically and are there any
circumstances where we need to be concerned about this phenomenon?

The velocity factor for air dielectric cables is essentially unity. The
slowest common velocity factor is about 0.66, which you'll find in coax
(where the field is entirely in the dielectric) having solid
polyethylene dielectric. Velocity factor is important in determining the
physical length of cable needed to effect a specific time or phase delay.

Roy Lewallen, W7EL

On Thu, 11 Feb 2010 07:59:23 -0800 (PST), phaedrus
wrote:

How much is the signal speed retarded by typically and are there any
circumstances where we need to be concerned about this phenomenon?

Look up the velocity factor, a simple multiplier/divider of the
relative speed of light in a transmission line. This means that the
signal that hits your antenna will hit your radio over the air before
that same signal reaches it through the transmission line.

73's
Richard Clark, KB7QHC

On Feb 11, 6:04*pm, Roy Lewallen wrote:
phaedrus wrote:
Just need to get these things clarified!

The velocity factor of a tx line is governed by its distributed
inductance and capacitance, is it not?

Yes.

I mean the more L and C you have per meter of line the lower the
signal velocity, right?

Right.

How much is the signal speed retarded by typically and are there any
circumstances where we need to be concerned about this phenomenon?

The velocity factor for air dielectric cables is essentially unity. The
slowest common velocity factor is about 0.66, which you'll find in coax
(where the field is entirely in the dielectric) having solid
polyethylene dielectric. Velocity factor is important in determining the
physical length of cable needed to effect a specific time or phase delay.

Roy Lewallen, W7EL

it is also important when you try to get cables to reach a certain
distance and still be a given phase length. this is why foam coax is
specified for 1/4 wave lines feeding most 4-square vertical systems.
a solid dielectric line 1/4 wave long is too short to reach from the
center to the feedpoints.

On Feb 11, 7:59*am, phaedrus wrote:
Just need to get these things clarified!

The velocity factor of a tx line is governed by its distributed
inductance and capacitance, is it not?
I mean the more L and C you have per meter of line the lower the
signal velocity, right?
How much is the signal speed retarded by typically and are there any
circumstances where we need to be concerned about this phenomenon?

Something not mentioned by other replies I've seen: some transmission
lines are made specifically to get delay. They are generally called
delay lines. Typical construction is to use a helical coil for the
center conductor, to increase inductance per unit length.

In straight TEM transmission line (typical coax), the propagation
velocity is the same as the speed of light (or more properly of
electromagnetic radiation of the same frequency) in the dielectric.
For any dielectric I've seen used in transmission lines, that's just
free-space speed of light times 1/(relative dielectric constant) of
the dielectric. If the magnetic properties of the dielectric differ
from those of a vacuum, you also have to consider that.

You need to consider velocity factor any time you're concerned with
the phase shift of the signal propagating through the line: phasing
lines for antennas, impedance measurements made by an instrument at
one end of the line of the impedance of a load at the other end of the
line, how long it takes a signal to propagate over the line, ...

Cheers,
Tom