ON THE 768 TYPE RADIO SEISMIC TELEMETRY EQUIPMENT

The type 768 radio seismic telemetry equipment has been designed for the use in case when installation between points of a seismic station network is difficult or in those places where the line capacity is not enough. Of course, it can also meet the need in the areas immediately after the occurrences of destructive earthquakes.It consists of a pair of ultra shortwave transmitter and receiver. A double frequency modulation was adopted. Not only it can be directly connected to a single component short period seismometer to transmit seismic analogue signals within the frequency range of 0.5 hz to 25 Hz, but also be used in combination with the specially designed multiple-channel digital telemetry system to transmit 0.2 Hz to 20 Hz CHDB4 code (compatible high density binary code). Therefore this equipment is capable to transmit signals like geoelectirc, geomagnetic, ground stress, ground tilt and many other geophysical quantities.Since July 1977, this equipment has been put to actual transmision test at the seismic station networks of Peking, Shanghai and Tientsin. After that, it was installed at the seismic station network of Kunming for more than one year. The results show that this equipment is superior in its portability, sensitivity, stability and immunity from disturbances. For a sufficient antenna height, the distance of transmission can reach about 115 kilometers.