A casing has a flat plate for being irradiated with a radiation from an external source, a plurality of metal plates disposed on edges of inner surfaces of ends of the flat plate, and a plurality of resin frames integrally molded on the ends of the flat plate in embedding relation to the metal plates. The primary and secondary cam each have an outer circumferential surface that defines a receiving portion and a cam surface. The SIP client manager receives SIP messages through a network interface. In some cases the contents of the byte cache layer may be stored as objects within the object cache. The microprocessor configures at least one unused channel placed in parallel with one of the operating channels for searching andor tracking the same visible satellite, the unused channel being configured so that the integration period of its integrator counter is different from that of the integrator counter of the operating channel.