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A data-transmission system has been developed which links four distant receiving sites of the U.S. Navy Space Surveillance system to a data-reduction center located at Dahlgren, Va. The receiving sites form a fence located on a great circle route across the southern United States from Georgia to California. Each receiver site is coupled to the data center by a commercial, voice-quality, duplex (two-way) telephone line. Standard FM telemetry techniques are used to transmit eight channels of analog data on each telephone line. These data are transmitted on eight discrete frequency-modulated carriers in a frequency band from 270 cps through 2455 cps. In addition to these FM data carriers, unmodulated tones are used for monitoring, compensation, and command functions. The data from each receiver site are permanently stored on paper recordings at the data-reduction center, so that this information can be assimilated at one location on a real-time basis. These data are used to compute the orbital parameters of satellites detected by the Space Surveillance system. The data-transmission system has been in operation for a year on a 24-hour basis with negligible down time. Off-line calibration techniques have been employed so that errors introduced into the data by the transmission system can be held to 2 per cent without interfering with the detection capabilities of the surveillance system. Tests indicate that the number of channels can be increased from 8 to 24 per telephone line by the use of crystal-controlled oscillators and crystal filters.