A properly chosen antenna can greatly enhance the quality of short-range shortwave broadcasting. Ideally, the antenna should handle high power to ensure high signal-to-noise ratio at the receiver, have a wide frequency bandwidth for selection of the appropriate frequency, allow diplexing of two transmitters on one antenna, and produce radiation at high elevation angles.

The Model 615 exhibits all the features of this ideal short-range broadcast antenna. Power-handling capability is 100 kW or 250 kW AM carrier power.

The frequency bandwidth is either 2.3-18 MHz or 3.2-18 MHz, and the radiation pattern is essentially omnidirectional with the majority of the energy directed overhead. Broadcast coverage is in the approximate range 0 to 1,500 kilometers from the transmitter station.

The 615 is truly a wideband antenna, and not merely tuned to the specific broadcast bands. It achieves high efficiency and low VSWR at any frequency within its operating range.

The 615 employs the same high-quality, exhaustively tested components and materials as all TCI antennas. Feedlines and catenaries are composed of a high-strength steel core and a highly conductive, corrosion-resistant, welded coating of aluminum. All feedline and radiator tip insulators are made of high-strength glazed alumina, a material with an extremely low loss tangent (.001), which is virtually impervious to the effects of ultraviolet radiation, dirt and salt spray.

Fiberglass material is not used anywhere in the antenna. Complete fabrication and preassembly are accomplished in the factory. Installation consists of only the tower erection and hoisting the preassembled curtains. The few connections required are accomplished with nuts and bolts.

The Model 613 is a truly broadband dipole antenna with excellent performance over short- and medium range circuits. The height and configuration of the antenna were chosen to provide high take-off angle radiation at the low frequencies optimum for short-range communication and low take-off angle radiation at the higher frequencies necessary for longer-range communications. At the take-off angles used in short- and medium-range communications, the azimuth pattern is essentially omnidirectional. This provides great flexibility and makes the 613 applicable to most communications requirements.

Maximise coverage over short to medium ranges.

The 613 achieves broadband coverage without the use of resistors or tuning units. It delivers full antenna efficiency—radiating valuable power rather than losing it in tuning devices.

The antenna’s vertical towers are a very important consideration for both installation and maintenance. Towers can be safely guyed prior to curtain installation. Once erected, the curtain can be lowered at any time, independent of the tower guying. Compared with long skewed towers, short vertical towers are much quicker to install, safer to climb, and easier to maintain.

The 613 uses the same high-quality, exhaustively tested components and materials featured in all TCI antennas. All radiators, feedlines, and catenaries are Alumoweld, a wire composed of a high-strength steel core and a highly conductive, corrosion-resistant welded aluminum coating.

Fixed-station antennas traditionally have used catenary and drop rod assemblies of fiberglass for its excellent dielectric and tensile strength properties. Field experience, however, has shown that minute, difficult-to-detect flaws in the material, RF burning, and small nicks incurred during installation can result in catastrophic structural failure and deterioration when stored for long periods at high temperature and high humidity. TCI antennas eliminate the risks stemming from the poor structural qualities of fiberglass by using Alumoweld catenaries, segmented by fail-safe insulators.

The Model 604ST is TCI’s answer to the medium wave broadcaster’s need for a high-quality, low- maintenance antenna for up to 600 kW broadcast applications. The 604ST uses a shunt-fed, guyed and grounded mast, which requires no antenna tuning unit (ATU). Tuning is performed by adjusting the shunt feed system at the time of installation.

The elimination of the ATU and the base insulator results in a simpler, lower cost configuration. The grounded tower design increases the antenna’s resistance to lightning strikes and also allows tower obstruction lights to be fed without the use of an isolation transformer, traditionally a high- maintenance item.

The 604ST is available in fourteen frequency ranges, covering the medium wave broadcast band, marine and weather bands, and non-directional beacon frequencies from 450 to 1840 kHz. Six ranges of transmitter carrier power levels are available, from 10 kW to 600 kW.

Install a low-maintenance solution for transmitters up to 600 kW.

The 604ST is just under one-quarter wavelength in height. The radiation pattern is omnidirectional; a second mast can be added as a parasitic reflector to achieve a directional pattern. A full copper earth radial system is included with each 604ST.

The 604ST uses the same high-quality materials as all other TCI antennas. The mast is hot-dipped galvanised steel, with a triangular cross section. The guy wires are Alumoweld (aluminum coated steel), segmented as necessary by a combination of compression and long-leakage-path tension insulators. Insulator materials are glazed ceramic. No organic materials, which could elongate or deteriorate over time, are used in the 604ST.

Optional accessories for the 604ST include an RF current meter, face mounted ladder, safety climbing cable, rest platforms, ICAO obstruction lights and paint.

The 604ST normally is erected by experienced rigging crews. TCI can quote installation tools, equipment, and field engineering assistance. Where site details are known in sufficient detail, TCI can provide quotations for turnkey systems.

Maximise gain and bandwidth with an exceptionally small structure

Highly reliable communications on long- range circuits require antennas with high power gain at low take-off angles. In addition, ionospheric variations resulting in frequent changes in frequency make a wide frequency bandwidth desirable. The conventional approach to achieve wideband, highly directive antennas has been to use multiple rhombic antennas, which rely heavily on end-fire gain to achieve their directivity and hence are quite large. Typical installations exceed 300 meters in length and require large investments in land.

Log-periodic antennas have long been desired for their wide band characteristics, efficient land use, and modest price.

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.