PROPOSED WORK WITH METHODOLOGY The C band covers the frequency range between 4 to 8 GHz The transponders operating at this frequency range are called C band transponders The basic transponder locks onto a constant carrier uplink tone and generates a constant carrier downlink tone which is phase coherent with the uplink aluminum shells present in the transponder maintains rigidity of the structure and provides electromagnetic shielding The power supply unit we use in this proposed transponder is a transformer coupled DC DC converter and it supplies regulated voltages to the transponder and its subsystems The down converter is used to supply the frequency conversion and the gain required for the functioning of the transponder In this there are two local oscillators that are made to get locked to a predetermined reference given by the coherent detector Variable gain amplifiers present in the down converter are also a subsystem of the automatic gain control AGC function The coherent detector reference generator consists of a final frequency translation stage It converts to a baseband signal which are meant to control the frequency control loop and the automatic gain control loop AGC The control voltage of the frequency control loop is used to tune a low noise voltage controlled crystal oscillator to keep track on the uplink carrier This reference is used to develop a down converter local oscillator signals and the coherent downlink carrier Like this uplink and downlink phases are kept in matching lockstep The functionality of this includes carrier detect circuitry and special switched bandwidth loop filters The transmitter has a local oscillator locked to the precision reference signal and a RF power amplifier
