Abstract :
The application of wideband technique to h.f. transmitters is described. The particular band dealt with is 2¿27.5 Mc/s, but the findings are not restricted to this band. The general principles of wideband power amplification are discussed, followed by a description of, and results obtained with, a 1 kW wideband amplifier which uses a modified distributed-amplifier technique. This not only permits better utilization of valves, but the amplifier is also less sensitive to varying output-load conditions. The amplifier may be used on a number of frequencies simultaneously. The use of wideband stages in conjunction with tunable stages in very-high-power transmitters is advantageous. The retuning of drives for a frequency change is avoided by the wideband mixer, which accepts an intelligence signal at 3.1 Mc/s and a frequency-determining signal, giving an output at the desired radiated frequency. Wideband transformers use ferrite cores, and introduce very small power loss. Transformers with a power rating of 40 kW are in use. The availability of wideband equipment simplifies the operation of transmitting stations. An arrangement particularly suitable for ground stations in air communication is described as an example of one of the many ways in which wideband equipment can be used.
