AbstractsEngineering

The present day necessity of installing multi-tower antenna arrays for many transmitters in the broadcast band (540 kc. to 1600 kc.) in order to prescribe the pattern of their radiated fields, brings with it the need for longer transmission lines. The transmission efficiency of a line should, of course, be a maximum compatible with economical installation and good engineering practice, since this portion of the system carries the most expensive energy of a transmitter plant. Furthermore, in Canada and the U.S. at least, government regulations limit the amount of power that can be lost in the external circuits i.e. power-dividing network, transmission line, and antenna-matching networks. Therefore, where two or more antennas are used requiring an equal number of antenna-matching circuits and a considerable length of transmission line, the losses in both of these components must be kept small in order to satisfy the regulations. These conditions draw attention to the relative merits of the two common types of line, the concentric tube and the open-wire. The characteristics, performance, and cost of concentric lines are well known, since they have been used for many years, and their various sizes have been standardized. In recent years, however, multi-conductor open-wire lines have been gaining favour. There are two factors which make it possible to approach the transmission efficiency of a concentric line, with an open-wire type.[...]