1 Nov. 2018 – Feeding Antennas, pt2 by Richard Porter, G3NII

Part two began with the use of ladder line in place of coax. An explanation followed as to why variations in design affect the characteristic impedance.  It was pointed out that window line is relatively easy to make for little cost.

Richard then moved on to the subject of the Aerial Tuning Unit, Aerial Matching Unit and the commercially produced ‘Matchbox’  All ultimately do the same thing but with losses. A point to look out for when building your own. The work done by Steve, G3TXQ was cited as a good reference.

This then led naturally on to SWR or VSWR and how the ATU is used to get the best transfer of power from rig to antenna.  Losses in coax led back to ladder lines and how they can be used successfully to transfer power with the least amount of loss.

Baluns were explained as well as the difference between a Voltage balun and a Current Balun. Here again Steve, G3TXQ website was cited as an excellent source of information. Richard showed some photos of baluns from the internet that were of poor construction although being presented as ‘how to do it’ projects.  The reasons why they were poor was explained. Considered also were choke baluns and numerous diagrams were shown and the  information presented on line by GM3SEK was recommended.

Richard ended his presentation by saying “Perhaps one of the most important points I want you to keep in mind is    DO NOT BUY CHEAP COAX”