Design of advanced HF receiver multicoupler for shipboard applications

This paper describes the design of a high level receiver multicoupler for the HF marine band. A wide-band class "A" push pull amplifier was designed using VMOSFET devices in conjunction with a feedforward linearization technique to obtain an 8-way ultralinear HF (1.5 to 30 MHz) receiver multicoupler. This technique resulted in an amplifier with intermodulation performance comparable to that of a 1 kW amplifier (class "A") but with only 170 Watts of DC power input. The intermodulation products are 70 dB down at input signal levels of +20 dBm, the noise figure is 8 dB and the 3 dB desensitization is 10 VRMS. An 8-way power divider with transmission line ferrite transformers and hybrids was designed to operate with negligible distortion and with input signal levels up to 10 Watts while providing 40 dB of isolation between any two output ports. This extremely low level of intermodulation distortion has necessitated the development of an in house measurement set up with residual intermodulation 15 to 20 dB below the measured values.