[Antennas] Back to Basics

Fri, 04 Jul 2003 13:10:45 -0700

Hi Durwydd,

The characteristic impedance of a coaxial transmission line is given by the
formula

Zo = (138/sqrt E) X log10 (D/d)

where "E" is the dielectric constant, "D" is the inner diameter of the outer
conductor and "d" is the outer diameter of the inner conductor,
respectively.

Here is a relevant link:

http://www.madisoncable.com/RFCoaxialCables.htm

The characteristic impedance of a transmission line is
frequency-independent, and is a function of physical dimensions and
dielectric constant. Thus, 50-ohm and 75-ohm coaxial cables have different
D/d ratios, assuming both use the same dielectric material.

Best 73,
Adam, VA7OJ/AB4OJ
North Vancouver, BC, Canada
http://www.qsl.net/ab4oj/

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Durwydd MacTara
Sent: Friday, July 04, 2003 12:56
To: [email protected]
Subject: [Antennas] Back to Basics

Since impedance is dependent on the frequency involved, what is the basis
for 52 ohm coax, and how does it differ from 75 ohm Coax?

  "Communications" is a People skill, the rest is technology.
             Durwydd MacTara

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