"AI4QJ" wrote in
:


"Owen Duffy" wrote in message
...
"AI4QJ" wrote in
:

I ran W8JI through the corum calculator. I got a super-well tuned
calculation of several coil parameters that I assume to be correct
for now, and surprise, phase angle is still close to 90 degrees
(what else could it be?). The beta axial propagation factor is 2.122
rad/m. I am trying to figure out the significance of that; it looks
like a velocity factor correction relative to a traveling wave in a
vacuum???

You have to view the helix as a transmission line.

The phase change along the transmission line representation of the
helix is 2.1 rad/m, so along 0.254m, there is a phase change of 0.53
rad or 30° in waves travelling along the line.

To help get your mind into gear, solve this problem:

You have 4.124m of RG58C/U, the far end is s/c, what is the apparent
inductance at 4MHz looking into the line.

Did you get 1.1uH?

I got 1.025uH using 250nH/m.

Well, it is about the right answer, but could be for the wrong reasons.

The line is 30° in length, and Zo is 50, so Xl is about 50*tan(30), then
work out L from there. Is that how you did it?



What is the electrical length of the line?

Electrical length at 4 MHz = 49.5 m assuming polyethylene dielectric.

VF=0.66, so the electrical length is 4.124/0.66m or 6.248m. That is
6.248/75 wl, or 30° (which you needed above).


What is Beta?

Beta = 0.08 rad/m for 75m

Beta=2*pi/75 rad/m or .083 rad/m... so I will pay 0.08.



Now apply the same thinking to the helix transmission line
equivalent.

Thanks Owen.