Test and Measurement Shortwave for long distance

Even in the age of fiber optics, satellite links and mobile connections, there is still a need for shortwave radio. New antennas and tuning units make it easier than ever to build high-performance systems, says Klaus Fischer product manager at Rohde & Schwarz


hortwave connections do not require any infrastructure, and communications is free aside from the one-time investment in the equipment. Major progress has been made in the development of secure, high-performance transmission methods, so shortwave transmission is still a valuable information medium, especially for public authorities and military users.

However, optimal transmission conditions are required to fully exploit the potential of this medium. Antennas play a key role. Losses at the antenna cannot be compensated elsewhere in the transmission path. Today’s wideband transmission methods need the best possible

signal-to-noise ratio, and that means optimized antennas. In addition to developing transceivers, Rohde & Schwarz has always been active in the development of high-performance, low-loss HF antennas. The latest result of these efforts is the R&S®HX002Hx series, which together with new antenna tuning units (ATU) and an innovative control and power supply unit is raising the HF air interface to a new level.

Fig. 1: The R&S®HX002H0 1 kW solution integrates the antenna and the tuning unit in an ultracompact unit.

Compact antenna solutions The shortwave bands, with frequencies between 1.5 MHz and 30 MHz, are based on long wavelengths up to more than 100 m. Depending on the antenna type, the necessary antenna dimensions can be just as large, resulting in high costs for the antenna itself and even more for the necessary installation space. In tight spaces, such as on ships or in urban environments, it might not even be possible to use them. This can be remedied by compact tunable dipole structures that feature high efficiency. For example, the R&S®HX002H0 1 kW solution and the R&S®HX002H3 150 W system (Figs. 1 and 2) offer outstanding HF performance despite their very compact dimensions of approximately 10 m × 5 m and provide 360-degree coverage for short, medium and long distances. A special version for ship deployment, the R&S®HX002H3M, can manage with antenna elements that are 50 % shorter, making it easier to install in the usually cramped superstructures of naval ships. All models feature single-mast mounting and a single coax cable connection to the junction unit.

Fig. 2: The R&S®HX002H3 150 W unit, consisting of an antenna and ATU, is very small for an HF unit.

Alternative wideband solutions in the form of resistor-damped dipoles (implemented as a loaded dipole, terminated folded dipole, inverted V, delta antenna, etc.), on the other hand, have barely acceptable gain even with significantly larger dimensions and are mainly used in special applications such as tactical deployment. These types are not part of the current portfolio.

Fig. 3: The R&S®FK002H0 1 kW antenna tuning unit can be operated at the base of various antennas.

28 October 2020

High-performance tuning units The new antenna tuning units and antenna/ tuning unit combination solutions are available in two power classes: 150 W and 1 kW (Fig. 3). They offer superior tuning characteristics over the entire HF frequency range and can be used to tune a wide variety of antennas, including

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electrically very short antennas, delivering high efficiency without internal damping. HF antennas are sensitive to their environment. For optimal results, the antenna environment has to be taken into account when tuning. A smart algorithm allows the new ATUs to include site factors during tuning to consistently achieve a VSWR of less than 1.3. The necessary internal circuitry with low-loss capacitors and air-core coils is learned and stored for each tuned frequency during a one-time up-front learning phase. So when a frequency change occurs during later operation, the right compensation components can be quickly switched on without further fine tuning. If no command is received from the transceiver, the antenna/ ATU can detect the frequency change itself.

Easy connection

All ATUs and antennas with integrated ATUs are powered and controlled by an R&S®GX002 junction unit (Fig. 4). The unit fits seamlessly into the operating concept of the latest shortwave transceiver generation. It is also ideal for use in legacy applications with older Rohde & Schwarz transceivers and with transceivers from other manufacturers thanks to its universal interfaces, including LAN and optical ports. And separating the antenna/ATU from the control unit allows different forms of integration into a high-level communications system. Depending on the configuration, different levels of functionality can be achieved that range from simple frequency switching with basic commands to support for state- of-the-art transmission methods. Fig. 5 shows two possible alternatives.

Fig. 4: The R&S®GX002 universal junction unit powers the antenna and the tuning unit, passes on the HF signal, and manages data exchange between the transceiver and tuning unit.

Fig. 5: Basic setup with a state-of-the-art Rohde&Schwarz transceiver (top) and with system components from other manufacturers (bottom). The junction unit not only offers diverse system configuration options, only one coax cable is needed to connect to the antenna/ATU. The cable carries the HF signal, the control signals and the DC supply voltage. This saves money, simplifies system integration and increases operational reliability.

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