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Automatu* Transmitter Switching łujuipinenl

Broadcasters using the 831H FM transmitters can realize the optimum in reliability and ease of maintenance through addition of the optional automatic switching and control equipment. This provides switching to a hot standby exciter in the dual configuration, or the complete isolation of a power amplifier in the case of failure or routine maintenance. These switching units are completely solid State utilizing integrated circuits to perform the necessary logie, and led's (light emitting diodes) for condition indicators. In addition to providing local control, the units may be remoted for convenience. The combination of logie circuits and motor-driven coax switches gives complete and ac-curate switching in the matter of seconds instead of minutes as required for manuał operation. A complete interlock prevents inadvertent operation of the amplifiers into a no-load condition.

377C-I

The Collins 377C-1 Automatic Exciter Switcher provides monitoring and control for two 31 OZ Exciters or similar units. If one unit fails, the 377C-1 automatically transfers the standby unit on the linę.

While in the hot standby modę, an exciter is maintained at 5-10% of normal power, thus conserving both power and equipment. When the unit is switched on the air, it comes to fuli power in less than 100 milliseconds. In addition, an indicator flashes to show which exciter is defective. eliminating the possibility of turning off the wrong unit for servicing. Included in the 377C-1 are facilities to switch station monitors to the dummy load for servicing of the exciter that is not on the air.

3771)1

The Collins 377D-1 Automatic Combiner Control provides automatic or manuał control of two power amplifiers and a three-switch combiner for parallel transmitter operation. The 377D-1 automatically assures maximum available power to the antenna at all times. If a failure occurs in either power amplifier. the remaining amplifier is switched to the antenna. while the defective one is switched to the dummy load. The 377D-1 provides all interlock functions for two amplifiers to assure proper sequencing and power-ing up.

The 377D-1 is completely solid State, with integrated circuits being utilized to provide the reliable digital control that this unit offers. To provide an indication of the several modes of operation that are available, a series of red and green light emitting diodes are used in the form of a flow chart on the front panel. At a glance, the engineer can tell exactly what transmitter is on the linę, and what path the

RF is taking to get to the antenna. An internal ni-cad battery supply across the dc power supply, assures that in the event of total power failure, the logie circuits remember what modę of operation the system was in. thus making return to the air as simple as possible.

In actual operation. the 377D-1 monitors the outputs of two independent power amplifiers continuously. and in the event of outright failure of either amplifier, will automatically initiate a transfei command to place the other amplifier directly on the air, bypassing the combiner. Time delay between failure and automatic transfer initiation is adjustable from 1 second to several minutes. The 377D-1 may also be used to automatically switch a "hot standby" transmitter or power amplifier into service in alternate main installations.

377C l Automatic Cxciter Switchover 377D-1 Automatic Combiner Control

The command signal that the logie circuitry generates is routed to both the proper switching elements. and a logie comparison system. Before ac power is applied to the coaxial switches. two rf sensing gates must be opened, denoting that there is no rf present on the switches. This process is accelerated by supplying a muting pulse to the exciter in use, and by opening the power amplifier interlock circuits. When complete shutdown is confirmed by the rf gates. ac power is applied to the coaxial switches. When the switches have transferred to their assigned positions, interlock readback logie is compared to the preprogrammed logie for the selected modę and the proper amplifier or amplifiers are returned to the air. The defective power amplifier is automatically placed on the dummy load for servicing. Its interlock circuits are opened until the dummy load air or water flow interlock is closed.

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