The design of the INMARSAT-3 frequency generator

The author describes a lightweight frequency generator containing a total of 29 frequency synthesizers including its redundancy circuits. Output frequencies range from 5125 MHz to 204 MHz and outputs from thirteen of the synthesizers at around 1150 MHz are commandable in 500 kHz steps over a range of 26 MHz. A prime consideration in the equipment design has been its low mass which nominally amounts to 200 gms per synthesizer including the contribution of equipment DC/DC converters, command and telemetry interfaces and reference generation circuits. The design, which has been undertaken over the past 16 months is based on high packing density using unsealed thick film alumina substrates with surface mounted components: all active components are, however, hermetically sealed