ARRL

Secure Site Login

Transmission Lines

Introduction

Understanding transmission lines is a vital part of the art of radio--the proper selection and use of a feedline is more important than the choice of radio. This is particularly true of multiband antennas fed with tuners--you can lose several S-units of transmit signal strength by making poor choices.

Articles

 

Web Links

Transmission lines  Transmission line concepts and an online transmission line calculator by Owen Duffy, VK1OD

Transmission Line Details by Dan AC6LA.  Free Windows program for calculating the loss and impedance transformation.

 Kenneth L. Nist, KQ6QV has free software for calculating arbitrary transmission line impedance, as well as transmission line equations for Mathcad 11.

atlc - Arbitrary Transmission Line Calculator (for transmission lines and directional couplers) by Dr. David Kirkby (G8WRB), who works at the department of Medical Physics, University College London.

Surplus Cable TV Coax

Sometime available for free or very low cost, many hams would like to know whether cheap 75 ohm TV coax can be used for ham radio. If a transmatch is normally used, as in the case with the popular G5RV multi-band antenna, there will be very little difference substituting 75 for 50 ohm cable.  As will be the case with a  600W tube type amp, which has an adjustable output network that can handle a minor SWR mismatch.  It is tough to solder to the aluminum shield of RG-6, but compression crimp BNC or F connectors are reasonably priced and adapters can be used to connect them to UHF connectors.

Using 1/2-Inch 75-ohm CATV Hardline, QST, The World Above 50 MHz, January 2000 p. 91.
How to attach PL-259s using hose clamps and a homebrew aluminum adapter sleeve.