Because of seasonal and diurnal variations of the ionosphere, shortwave broadcasters have found it necessary to change frequencies at regular intervals. Frequency changes can be simplified with the use of wideband, frequency-independent antennas. The Model 515 and 516 high-power log-periodic antennas are well suited for this application.
For medium-range broadcasting (700 km to 3000 km) moderate transmitter power and high take-off angles are required. The Model 515 and 516 log- periodic antennas are optimum for this application, and have the ability to handle 100 kW carrier power with 100% modulation. A version of the Model 516 is available that can handle 250 kW with 100% modulation.
The 515 provides take-off angles of 30 to 45 degrees, and the 516 provides a take-off angle of 21 degrees for slightly longer paths. Both antennas have negligible side and back lobes, low VSWR, and are extremely efficient, resulting in high ERP and received signal level.
Combine frequency independence with high ERP
The radiator design is the equivalent of “fattened” radiators with lowered Q and reduced voltage stress. These radiators also increase the effective “active region” radiating length in each curtain, resulting in greater radiation efficiency and higher power gain. TCI analytical techniques provide large volumetrical apertures and resultant high power gain while maintaining log-periodic performance.
As with all TCI antennas, the 515 and 516 utilise high-quality, rugged, exhaustively tested components and materials. No fiberglass assemblies are used. Alumoweld wire, segmented where necessary with high-quality ceramic fail-safe insulators, is used to provide long and trouble-free service life. Carefully tested corona-protection details are employed where necessary in the curtain. No dissimilar contacts, which have historically been the major cause of corrosion, exist anywhere in the tower structure or antenna curtains.
A precisely manufactured, electrically transparent Alumoweld structure is used instead.
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