Requirements for high-quality geodetic VLBI observation

In order to obtain high-quality VLBI data, system must meet the following requirements.   High-speed antenna movement

VLBI observation requires a antenna which has high speed movement to observe a large number of quasars at the same time. VLBI system has to receive as many quasars as possible for accuracy improvement of positioning.   Broadband antenna

The basin can be collected more rainwater than the cup. On the same principle, a large size of antenna is required to receive a variety of radio signals.   Suitable receiver

VLBI antenna receives all kinds of radio signals from space, satellites and cell phones. Among these signals, the exact signal which is correspond to its own purpose must be received.   Extremely sensitive clock

Each VLBI station should detect exact arrival time of electromagnetic waves from the source. In arrival of electromagnetic waves, differential time delay occurs between different VLBI observatories because of earth curvature. Using this difference of time, the speed of light and position of the source, exact distance between different observatories can be determined. Therefore, extremely sensitive clock is required.