Journal of the Society of Motion Picture Engineers (1930-1949)

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receiver bus as a production line and also as an emergency audio transmitter in case of failure of the main 45-w equipment. The transmitter bus can operate on either a three-phase, four-wire, 220/110v or a single-phase 1 1 0-v system. Three variacs used in conjunction with a voltmeter provide for balancing the load. The Transmitter Power Bus A serious difficulty in most remote pickup setups is power availability. The purpose of this vehicle is to remove this problem. It houses two 15-kva motor generators in a compartment just aft of the cab. A single 55-gal gas tank serves both the bus and generator motors. This allows the generators to run under full load for ten hours without refueling which is more than enough time for the average demonstration. The generators supply three-phase 208/11 0-v power to two Russell and Stoll output plugs located on the side of the bus. By connecting the output of each generator to the arm of a 3-pole, double-throw switch either generator can feed either plug or in emergency any one generator both plugs. The governor on the motor holds the output frequency within a half-cycle once it has been adjusted for a constant load. By operating the synchronizing generators with a long time-constant in the AFC circuit they lock in very well on 60 cycles. Two 250-ft reels of fourwire jf6 power cable are utilized to keep the line losses low while separating the vehicles to minimize the generator noise in the audio pickup. Two other reels carry additional camera cable, RG-11U coaxial cable for video feeds, and twowire #10 cable for lighting and power extensions. The reels are accessible from the outside by the use of small ports in the side of the bus. The rear compartment of this vehicle contains two work benches for equipment maintenance. Below the benches and the reels are cabinets and drawers for spare parts and tools. The drawers have removable dividers for greater utilization of space. The Receiver Bus As its name implies this vehicle provides the receiving facilities for the system. This consists of ten 16-in. receivers and one large-screen projection receiver which have been modified so that they are capable of being either "line" or "air" fed. As was mentioned previously, this unit may be located up to 20 miles from the point of program origin. Most of the equipment used in reception is contained in two 6-ft racks mounted in the rear of the bus. Two doors make the back of the rack easily accessible from the outside. Video signal from the microwave receiver is passed through a stabilizing amplifier to clean up the synchronizing pulses and to make sure of the synchronizing pulse-to-video signal percentage. This stabilizing amplifier has two outputs, one of which feeds a 12-in. monitor mounted alongside the rack and the other feeds two unity-gain distribution amplifiers having ten isolated outputs. The input and output of all equipment comes up on coaxial patch panels with parallel jacks for versatility and quick checking with an oscilloscope. In the present setup the output from one of the distribution amplifiers feeds a "Dumitter." The Dumitter is a closed circuit (nonradiating) transmitter whose function is to take audio and composite video signals and modulate a carrier on television channel 3. This modulated RF signal can then be sent over coaxial line to as many as 125 commercial receivers of 72-ohm input using a line distribution arrangement without modifying the receiver to a line-driven monitor. Small distribution boxes are provided with the Dumitter having one input and five outputs. By utilizing these boxes all ten receivers may be 466 December 1952 Journal of the SMPTE Vol.59