The paper presents specifications, architecture, new design concepts and challenges faced and resolved during hardware realization of on-orbit frequency programmable C-Band Telemetry and Ranging transmitter developed for Indian GEOSAT Programme. The transmitter can be programmed to on-board C-Band frequency (4.185 GHz-4.2 GHz) with a resolution of 610 Hz by issuing a 16 bit command from ground station. It uses digital programming capability of Ultra CMOS based PLL Synthesizer chip to program the carrier frequency. Conventional TT&C transmitters do not provide flexibility to the satellite operator to change it's transmit frequency at the later stage in view of in-orbit interference. Programming concept will enable the mission to re-program on-board TT&C frequencies in case of interference from co-located satellites.
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