[Antennas] Re: 600 Ohm Ladder Line

[Pastor-kc1di]

There is one commercial source that I know of it's found at=0D
 http://www.w7fg.com/ant.htm=0D
=0D
73 dave =0D
=0D
-------Original Message-------=0D
 =0D
From: Barry L. Ornitz=0D
Date: Sunday, November 10, 2002 01:34:35=0D
To: antennas@mailman.qth.net=0D
Cc: durwydd@hotmail.com=0D
Subject: [Antennas] Re: 600 Ohm Ladder Line=0D
 =0D
Durwydd MacTara asked:=0D
=0D
> I need the necessary formula(e) to make some 600 ohm ladder =0D
> line. This stuff is almost impossible to find in today's =0D
> market! Also need to make some from resistance wire for a =0D
> 500W termination for a non resonant Rhombic.=0D
=0D
For two wires of equal diameter, d, and center to center =0D
spacing of D, the equation for the impedance of the parallel =0D
wires in air is:=0D
=0D
Z =3D 120 *arccosh(D/d) [Eqn. 1]=0D
=0D
where: arcosh(x) =3D inverse hyperbolic cosine(x) =0D
=3D ln(x + sqrt(x^2-1)).=0D
=0D
Note that this formula is slightly more accurate than the one =0D
published by the ARRL in their various handbooks. If you make =0D
the assumption that the ratio of the diameters is very large, =0D
you can approximate the arccosh by using the logarithm of 2*x =0D
instead. Then if you use base 10 logs instead of natural =0D
logs, you get the more commonly found equation:=0D
=0D
Z ~ 276*log10(2*D/d) [Eqn. 2]=0D
=0D
If the wire is #12 AWG (diameter 0.0808 inches), and the =0D
spacing is 6 inches the impedances are:=0D
=0D
Z =3D 120 * arccosh(6/0.0808) =3D 600.076 ohms from Eqn. 1, =0D
and=0D
Z =3D 276 * log10(12/0.0808) =3D 599.408 ohms from Eqn. 2.=0D
=0D
So the approximation is quite good for large ratios of sizes, =0D
but for 0.125 inch spacing, the differences are more =0D
significant: 120.402 ohms versus 135 ohms for the =0D
simplification.=0D
=0D
For the resistive termination, high loss transmission line is =0D
generally used if you cannot find the necessary high power =0D
non-inductive resistor. Laport's book, "Radio Antenna =0D
Engineering", suggests the use of galvanized steel or =0D
stainless in making these transmission lines. The idea is to =0D
use a high resistivity material, and if it is magnetic =0D
(permeability greater than unity) the losses will be all that =0D
much higher. Nichrome alloys are also in common use. Small =0D
gauge stainless welding wire is more commonly available.=0D
=0D
For those interested in rhombic antennas and their various =0D
cousins (half-rhombics, Vee's, and terminated longwires), =0D
Laport's book is the "Bible". It has been out of print for =0D
many years, but the demand is still high as evidenced by the =0D
scarcity of used books and the high prices they bring when =0D
they do appear.=0D
=0D
73, Dr. Barry L. Ornitz WA4VZQ ornitz@tricon.net=0D
=0D
- - - =0D
=0D
Your moderator for this list is:=0D
Larry Wilson KE1HZ antennas-owner@mailman.qth.net=0D
_______________________________________________=0D
Antennas mailing list=0D
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