Cherry & White were approached by Astrium to design and manufacture an RS530, 3 clock, asymmetric fibre optic modem and chassis system that would operate at data rates between 70bps to 10Mbps. The timescale for this project was very short, so the modems were produced in little over 3 months. These were to be used in conjunction with the Skynet 5 Satellite System, the modems operate on Naval ships and in Satellite Ground Stations.
The modems were designed to be placed into a chassis that is no bigger than 3U that provides power redundancy, the CW4000 chassis was designed along side the modems and can accommodate up to 17 CW4002 modems. The CW4002 was also designed to work in 6 operation modes:
- X21 External Clock – This Mode uses a single clock received from the X21 interface.
- X21 Internal Clock – Similar to X21 External clock except that the clock is generated by one of the CW4002s.
- RS530 Mode 1 – This Mode uses two independent co-directional clocks received from the RS530 interface.
- RS530 Mode 2 – Similar to RS530 mode 1 except that the clocks are in the same direction.
- RS530 3 Clock Asymmetric – Uses a third clock input looped back in the external equipment to overcome timing problems with high speed transmission.
- RS530 3 Clock Symmetric – Similar to RS530 3 Clock Asymmetric except that the clocks are not independent.