Got several answers to my question so here goes. I will list the source
if the author sent it.
For square coax with air dielectric, to a very good approximation, the
impedance is 138log (D/d). That is the same as for round coax.
attributed to OZ2OE:
Z0 = (138/E) * log10 (1.08 * D/d) (for circular inner and square
outer conductor) E = dielectric constant of insulation: (1 = air)
page 24-22 of Reference Data for Radio Engineers, 6th edition, by ITT.
Zo approx= [138 log10 (p) + 6.48 - 2.34(1+0.405p^-4)/(1-0.405p^-4)
-.48(1+0.163p^-8)/(1-0.163p^ -8) - .12
(1+0.067(p)^-12)/(1-0.067(p)^-12)]e^-0.5
Where D is the square dimension and d is the inner diameter and p= D/d
The RSGB "The VHF/UHF DX Book" (p. 7-34) says:
Zo = 138log [1.08 (D/d)]
Where: log is base 10
D is the inner width of the square tubing
d is the outer diameter of the center conductor (and is centered in the
tube) Obviously, D & d should be in the same units (do not mean to insult
intelligence).
If the length of a side of the square is s, then the diameter of the
equivalent circle is 2*s/(the square root of pi), or approximately 1.128*s.
The impedance of square coax (with center conductor in the middle)
is 138*log((1.178D)/d). D is the inner wall length of the enclosure,
and d is the dia of the center conductor. (both in same units!!
It doesn't work that way. The Radio Engineers Handbook or the Reference
Data Book for Engineers has formulas for square transmission lines.
http://fermi.la.asu.edu/w9cf/equiv/index.html
http://fermi.la.asu.edu/w9cf/articles/square/index.html
Thanks again for the help
Art
KB7WW
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