Main station which is also what we call center station or hub, is main part of VSAT network. And it is the same to normal earth station. Large antennas will be used in the hub, and the diameter is often Ku-band 3.5m to 3.8m or C-band 7m to 13m with HPA, LNA, Up/Down Converter, Modem, data interface equipment...etc. Hub and main computers are often placed together, or hub is connected with the main computer by other ways, like earth or satellite.
Typically, a network control center is set in the hub or other places so as to monitor, manage, control and maintain the full network. The network control center is used to monitor and manage the operational status of the full network, like real-time monitoring, diagnosis the working status, testing channel quality, responsible channel assignment, statistics and billing for each small station and hub. The failure of main station will affect the normal work of the overall network as the main station involves the whole VSAT operation. Thus, the backup is set for all the devices, hub often adopts modular structure, and the device adopts the way of high-speed interconnect in order to be easy in reorganization.
VSAT small station consists of small diameter antennas, outdoor unit and indoor unit. VSAT antennas have two types, one is prime focus antenna and the other is off-set antenna. Prime focus antenna has large diameter. However, off-set antenna has characteristics of small diameter, good performance (high gain, low sidelobe), for its structure it's not easy to collect snow, so off-set antennas are often be adopted. Outdoor unit is mainly composed of CaAsFET solid amplifier, low-noise FET amplifier, upper/down converter and corresponding monitoring circuit...etc. The whole unit can be placed in a metal box and hang on the back of the reflector. Indoor unit is mainly composed of modem, encoder and data interface equipment. Indoor and outdoor unit are connected by coaxial cable, send low-IF signal and power supply. The whole equipment has characteristics of compact structure, low-cost, full solid, easy installation, low environment requirements, which can be connected with data terminals(computer, data communication equipment, fax, Telex...etc), without ground relay lines.