The Antenna Tuning Unit at Burg

BURG, Germany — Malfunction of a transmitting system can cause severe damage in sensitive broadcast equipment, affecting reliability and performance. To meet the specific requirements of communication services, Transradio realizes transmitting systems offering redundancy of vital system components.

Transradio recently undertook the task of improving the operational stability of a communication service provided by Europäischen Funkrundsteuerung GmbH (EFR) for energy management, lighting control, smart metering and data services. The transmission from Burg, once one of the biggest German broadcast radio stations, is now operated by Media Broadcast on 139 kHz.

Antenna

At the site, a 50 kW reserve Transradio TRAM transmitter automatically backs up the main 100 kW TRAM transmitter in case of failure. Both transmitters are very efficient and perform well and thus are used for LF time signal broadcasting.

The Burg antenna system comprises a 324-meter/1,063-foot grounded lattice mast supporting a rhombic cage antenna and a 210-meter/670-foot base insulated tube mast. The height of the tube mast, originally designed for medium-wave broadcasting, is low compared to the LF wavelength. High voltages appear at the mast base and cause unstable operation. By changing the tube mast isolation design and using part of the upper­most guy section as top-load capacitance, voltages at the mast base were reduced to less than a half.

To maintain transmission of the signal in case of a disturbance in one of the antennas or antenna tuning units, Transradio implemented a sophisticated, customized antenna control and switchover system based on a programmable logic controller. This system takes into account and covers all relevant parameters of the transmitting installation, including status monitoring of safety equipment such as UV detectors, access doors and earth grounds.

The antenna tuning unit of the old cage antenna was replaced by a carefully shielded container equipped with motor-driven grounding switches. After completing antenna modification, the antenna tuning unit of the tube mast was upgraded for switchover and matched to the changed base impedance. Properly adjusted spark gaps at all relevant positions of the matching circuit protect the equipment against excess voltage when lightning strikes.

For information, contact Michael Schmolke at Transradio in Germany at 011-49-30-339781-305 or visit www.tsb-ag.de