Communication Handler

COMH is basically an 80C186 -16-bit micro-controller based card working at a clock speed of 6 MHz.This card also contains a Zilog 85C30 dual channel COMMUNICATION CONTROLLER which handles SDLC/HDLC communication thro' Channel A @ 125 Kbits/sec,asynchronous communication @ 38.4 Kbits/sec for communicating with ANTCOM and PC router respectively.Intel 29C17 CODEC (VOICE CODER-DECODER) handles voice communication @ 62.5 Kbits/sec , digital Phase Lock Loop and other combinational logic handles clock recovery and bit interleaving functions and FSK MODEM chips NE 5080 and NE 5081 handles FSK modulation and demodulation.

COMH multiplexes command data(125 Kbits/sec),digitized voice(62.5 Kbits) , synchronisation pulses,dial pulses and two aux. channels into a single bit stream of 250 Kbits/sec .

 Voice and Data multiplexer (VDM) block diagram shows the details of the multiplexer and the next block diagram of the multiplexed data frame BIT INTERLEAVING shows how the various data bits are assembled and packed into a single bit stream.The bottom figure also shows the flow diagram of the SYNC DETECTOR state machine.The VDM output (250 Kbits/sec) is sent to the FSK MODEM for converting into analog FSK signals of appropriate power and combined with the LO carriers (FORWARD LINK) and sent to the OF system for converting into optical signals @ 1310 nm.

Next,let us see how the system at the antenna end receives this Optical signal and is converted into a command information for the SERVO or MCM ?