Electrically small antennas can be used to advantage in a wide range of receiving applications. The inefficiencies inherent in small antennas have the same effect as other sources of noise on the signal-to- noise ratio. When external noise is greater than the noise from antenna inefficiency (and internal electronics, if present), an antenna is said to be “externally noise limited.” In this case, the higher level of external noise dominates the system signal-to-noise ratio, rendering the internal noise insignificant. Thus, when external noise is relatively high, small receiving antennas can work as well as full-size, fully efficient antennas. This also means that fully efficient antennas need to be located at electrically quiet sites to achieve their full potential.

A loop antenna functions as a magnetic dipole. An incident electromagnetic wave induces a current in the loop; a matching transformer inside the loop couples the induced current into a 50Q load, either an amplifier or a length of coax running to the receiver. 

The Model 545T transportable dual take-off angle antenna provides the features most desired in a tactical antenna required to communicate over any range at any azimuth. To achieve this performance, the Model 545T, and its fixed counterpart the 545F, are omnidirectional, and radiation is vertically steerable. They generate independent low and high beams, optimizing gain for any communications distance. The 545 is a four-arm spiral antenna that can be excited in two orthogonal modes, each of which is horizontally polarized and essentially omni-azimuthal at all elevation angles. The 545 can be operated in the low-angle mode only, the high-angle mode only, or low-angle and high-angle modes simultaneously.

The 545T is highly transportable and quickly deployable. The materials in the 545T are selected for their ruggedness, light weight and ease of handling. The supporting tower is made of lightweight, high-strength aluminum. It is supplied in nesting 3.1-meter (10-foot) sections for easy assembly. The antenna curtain wires are flexible bronze. Careful attention is given to the fittings and connection details so assembly is simple, rapid, and foolproof. With a trained crew of five persons, the 545T maybe installed and made operational in less than an hour. The 545T includes all the necessary hardware, tools, and 50 ohm transformer. A hand winch and rope snubbers are provided to facilitate quick erection. All guy anchors are included in the tower package, along with sturdy transit cases and instructions for assembly and disassembly.

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 utilize 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.

Most communicators are well aware of the problems associated with “close-in” HF communications. Frequently it is easier to raise a station 2,000 km away than one’s base of operations 100 miles distant. To a large extent, the problems of short-range communications are related to inadequate antenna performance. Traditional antenna performance suffers from one or more of the following limitations:

• Inadequate bandwidth and efficiency. 

• No shortrange broadband antenna before the 501 covered the most important lower frequencies down to 2 MHz with adequate efficiency.

• Improper pattern.

• Vertically polarized radiators do not support the skywave.

The performance of the Model 501 is tailored for the short-range and close-in sectoral coverage applications. The 501 radiates a broad, upwardly directed beam, slightly biased in one direction. Thus, it serves well for broad sectoral coverage and for short-range point-to-point.

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.

Maximize 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.