Continuous real-time Analog signals are produced by the short-period seismometers in our network. These signals are telemetered through FM (frequency modulated) radio technology. A VCO (voltage controlled oscillator) transforms the seismometer signal into frequency variations of a FM carrier frequency. The FM signal may be carried by radio waves, microwave, telephone line, or T-1 communications cable. At the Seismology Lab, a "Discriminator" is used to separate the signal from the carrier. Analog signals must be digitized and time stamped before they can be combined with other data.
Broad-band and Strong Motion instruments in the PNSN are equipped with electronics packages that digitize and time-stamp the data at each local site. Digital data is sent to the PNSN Seismology Lab via leased-line modems, Internet connections, Cell modems, and VSAT satellite communc