POWER SUPPLIES

3-7 Figure 3-6.—Rf amplifier unit. POWER SUPPLIES.—One power supply produces operating voltages for the amplifier when operating from a 60-hertz power source. All components of the power supply, except the power transformers, are mounted on a chassis and panel assembly that is hinge-mounted to a metal case. The power transformers are constructed as part of the case and there are no operating controls. The other power supply produces operating voltages for the rf amplifier when a 400-hertz, three- phase, 115-volt primary power source is used. ANTENNA COUPLER GROUP.—The antenna coupler group is an automatic antenna tuning system. However, the equipment design includes provisions for manual or semiautomatic tuning. This makes the system adaptable for use with other radio transmitters. The manual tuning capability is useful when a failure occurs in the automatic tuning circuitry. Tuning can also be accomplished without the use of rf power (SILENT TUNING). This method is useful in installations where radio silence must be maintained except for brief transmission periods. The antenna coupler matches the impedance of a 15-, 25-, 28-, or 35-foot whip antenna to a 50-ohm transmission line at any frequency in the 2- to 30-megahertz range. Control signals from the associated antenna coupler control unit automatically tune the matching network in less than five seconds. During manual and silent operation, tuning is accomplished by the operator with the controls mounted on the antenna coupler control unit. A low power (not to exceed 250 watts) cw signal is required for tuning. Once tuned, the coupler is capable of handling 1,000 watts peak envelope power (pep). The coupler is enclosed in an aluminum, airtight, pressurized case. Six mounting feet enable the unit to be attached to the mast of a ship at the base of a whip antenna. The coupler is pressurized with dry nitrogen to aid internal heat transfer and to prevent corona and arcing. All components of the coupler are secured to a chassis that is mounted to the case so that an air duct exists between the chassis plate and the