25 Oct. 2018 – Feeding Antennas, pt1 by Richard Porter, G3NII

The programme began with an introduction to Oliver Heaviside, 1850 – 1925 who first produced screened cable which formed the basis for our coaxial cable. Richard detailed Oliver’s life which was beset with problems, no less than contracting Scarlet Fever at the age of eight leaving him deaf. In spite of this he became an acknowledged electrical engineer, mathematician and physicist, a member of the Royal Society and  predicted the ionosphere in 1920.

Richard stated that “now that coaxial cable had been invented, lets take a closer look at what’s involved and how it works”  There followed an in depth look at the construction and how that affects the overall characteristics. The various types were listed and how and why they were named. After this discussion it was pointed out that one should never buy cheap coax! Richard passed around samples of good and bad and explained why they were good and bad.

It was noted that coax feeding a dipole or any other balanced antenna will suffer from ‘common mode’ currents and further information was discussed as to why and how to deal with the problem.  Losses in coax were calculated according to coax type and the radio frequency being used.