On 4 abr, 19:13, Bob wrote:
Anyone know the velocity factor of JSC #1317 450 ohm line, 18 AWG?
Googling seems to give a variety of answers, and it's not posted at
the JSC site.

tnx,

Bob
k5qwg

Hello Bob,

I used the ATLC program to calculate the properties of weird
transmission lines. It accepts arbitrary shaped dielectric material.
It outputs the line properties. When you run two simulations (with
window and without window), you can average them to find the velocity
factor of the ladder line.

The program can be retrieved from atlc.sourceforge.net (also Windows
versions). When you hit the tutorial button, you can check whether it
is worth to spend the time.

Looking to the picture of the line, most important for Zo is the ratio
(bare wire diameter)/(wire + insulation diameter) as E-field is
highest close to the conductors. For a ballpark calculation, I would
use VF = 0.92.

You can also determine the quarter wave resonance length by
measurement and calculate the velocity factor, but then you need
several meters at hand. When you really need VF with high accuracy,
measuring is the best option (around the frequency of interest). As
the separation of the wires is very small (w.r.t. length), it is
probably not necessary to correct for fringing at the open end.

Maybe the vendor cannot guarantee VF, because he receives material
from different sources.

Best regards and good luck with determining VF,


Wim
PA3DJS
www.tetech.nl
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