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Figure 4. Components and dimensions of a typical remote seismograph station, similar to stations located on Fig. 3. The seismometer (a) converts small ground motions into an electric signal that has varying voltage. An amplifier and a voltage-controlled oscillator amplify this signal and convert it to a frequency-modulated (FM) tone. The radio transmitter (c) and the antenna (d) transmit the tone signal to the recording site.

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