Automatic transmission system
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An automatic transmission system (or occasionally automated transmission system, to avoid confusion with the automatic transmission of an automobile) is an automated system designed to keep a radio transmitter and antenna system running without direct human oversight or attention for long periods.
In the early days of radio, an operator, technician or electrical engineer was required to attend to a transmitter at any time it was operating or capable of operating. Any condition (such as distorted or off-frequency transmission) which could interfere with other radio services would require immediate manual intervention; facilities also had to be monitored for any fault conditions which could impair the transmitted signal or cause damage to the transmitting equipment.
As technology improved, transmitters became more reliable, and electromechanical means of checking and later correcting problems became commonplace. Regulations eventually caught up with these advances, and radio stations (both broadcast and non-broadcast, such as amateur radio repeaters) were allowed to run unattended provided that there was such an ATS installed.
Theory of operation
The system monitors conditions such as voltage, current, and temperature within the transmitter cabinet or enclosure, and often has external sensors as well, particularly on the antenna. Some systems have remote monitoring points which report back to the main unit though telemetry links, particularly for lower radio frequencies like AM radio where propagation changes from day to night.
Advanced systems can monitor and often correct other problems which are considered mission-critical, such as detecting ice on antenna elements or radomes and turning on heaters to prevent the VSWR (power reflected from a mismatched antenna back into the transmitter) from going too high. High-power stations which use desiccation pumps to put dry nitrogen in to their feedline (to displace moisture for increased efficiency) can also monitor the pressure. Generators, batteries, and incoming electricity can also be monitored.
If anything goes wrong which the ATS cannot handle, it can send out calls for help, via pager, telephone voice message, or dedicated telemetry links back to a fixed point such as a broadcast studio. Other than possibly listening for dead air from the studio/transmitter link, an ATS does not cover the programming or the studio equipment like broadcast automation, but rather only the "transmitter plant".