R&S^®SR600E1 FM Solid-State Transmitters

Exciter

The synthesized Exciter R&S® SU135 generates a frequency-modulated signal in the range 87.5 MHz to 108 MHz with a maximum output power of 20 W. AF, RDS or SCA signals are fed to the exciter as modulation signals. An additional module allows digital data in line with the bit-serial AES/EBU protocol to be processed instead of AF signals.

The transmitters are operated via menus, using the control and display elements on the exciter front panel. Settings such as transmit frequency, RF output power, operating and modulation modes, RF thresholds, module parameters, interfaces and system control can also be made in menus. Each of the six preset channels may be used to save the settings from the operating channel in non-volatile memory. For monitoring and control of the transmitters, various operating parameters of the VHF FM transmitter, such as air-pressure gradient, intake and outlet air temperatures or extensive absorber temperature, are registered and evaluated by the exciter. Measurement results and status (e.g. operating hours, system events) of the exciter as well as modulation data (e.g. frequency deviation, AF level), RF output power, reflected power and operating voltages of the VHF amplifiers are also evaluated and displayed. An error table supplements the monitoring functions. Should the control functions fail, the transmitter switches to a defined, risk-free state.

Amplifier

The 2.5 kW, 5 kW and 10 kW transmitters are provided with one, two or four Amplifiers VU320, where the signal is boosted to approx. 2.7 kW. The output amplifiers are of modular design, each consisting of nine identical 300 W basic modules and a 70 W preamplifier. The RF output power is set and regulated by varying the drain voltage of the output amplifiers. The harmonics filters in the amplifiers ensure an attenuation of harmonics of typically 76 dB. In the case of the Transmitter SR610E1 with 10 kW into 50 W, the 4:1 combiner sums the four input powers to a total power. All power combiners and splitters are in microstrip design and thus exhibit a low failure rate.

Power supply

The 2.5 kW and 5 kW transmitters use a single-stage power supply, i.e. a single transformer with rectifiers, while the 10 kW transmitter contains a dual-stage power supply consisting of two separate transformers with rectifiers. The 2.7 kW output amplifiers are each assigned a DC converter for generating the operating voltage required for the amplifiers. Since the output power is controlled via the operating voltage of the power transistors, an efficiency of at least 64% (without fan) is attained even in the event of a fault or operation below the rated power.

Transmitter rack

The 19-inch rack makes for economy of space, so the transmitters are particularly suitable for use in small-area transmitter stations. Air supply and RF connectors can optionally be fitted at the top or bottom of the rack. The transmitters are sup-plied with fans as standard. An external fan may be used provided the specifications are observed.