Chuck Colby

  First Mobile TV Units for the Army

December 1967 Instruments and Control Systems

Mobile TV Units For The Army
Charles Colby, Ampex Corporation
December 1967

The Army makes extensive use of closed circuit television; educational video tapes produced by live mobile TV units (Fig. 1) are played back on one of the world's largest closed circuit TV systems composed of 24 Army bases and schools.

Video tape eliminates or minimizes problems associated with film production and use. Instant replay of a scene for on-the-spot evaluation with no need for film developing, easier editing, and the ability to update, erase and reuse the tape are some of the advantates gained. Training tapes may also originate from a central source and be piped by closed circuit TV to hundreds of classrooms simultaneously, thus saving costs on duplicate films and film projectors. Much less time elapses between the tape's original production and its use in the classroom.

Video Vans

The mobile TV units are located on 30 ft. trailers, custom-built by Fruehauf to Ampex Corp specifications. The interiors of the vans provide three basic operating areas: video control area, audio control area, and Videotape recorder and film chain area. (Fig. 2).

Workbench areas at each end of a van are integrated with the storage facilities for three Ampex/Marconi 322V vidicon TV cameras, as well as storage for lenses, microphones, test equipment, spare parts, equipment manuals, records, films, and video tapes. Cabinets under the floor of the van, accessible from the outside, hold the microphone boom and stands, camera tripods and dollies, a lighting package, and eight camera cable reels on curbside with a total capacity of 1000 feet of camera cable.

An outboard connector panel, in the curbside reel storage compartment, enables connection of input and output cables to the van system. Connectors are: three video inputs, four microphone inputs, three auxilary audio input/outputs, two wireless microphone antenna inputs, and two TV transmitter RF outputs.

A working platform of the roof is fitted with recessed tiedowns for securing camera tripods under high wind conditions or while the van is in motion. A removable guard-rail provides further protection.

Video Control Area

Located at the center of the van, this area consists of three racks of equipment (Fig. 3). The main items consise of an Ampex control panel for remotely controlling three Ampex 322V vidicon cameras, Dynair video switcher/fader, special effects generator, and Dage film chain remote control panel, all grouped for easy operation by one man. Other equipment includes a Conrac 8 in. monitor and Tektronix 529 waveform monitor for each of the three cameras outside the van and for the film chain camera. Other Conrac 8 in. monitors in the control rack are for video tape, special effects, remote input and preview.

A Conrac 14 in. monitor and Tektronix RM-529 waveform monitor, along with an Ampex audio amplifier/speaker combination, monitor the program as it is taped or as it is fed directly from the van to an external video recorder or TV distribution system. Futher equipment includes a Dage dual sync generator, Synair video and pulse distribution amplifiers, Tele-Instruments, 12-channel RF transmitter for feeding standard TV sets directrly from the outboard connector panel, film chain camera control unit, audio and video patch panels, Alma audio distribution amplifier, Telemet video test signal generator, and rack AC power distribution panel.

Film Chain, Videotape Recorder Area

An Ampex VR-1100 videotape recorder with Inter- (continued below)

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sync servo system, Amtec time correction system, video processing amplifier and air-beating rotating video head, enable video and audio recording on a 2 in. wide magnetic tape. Up to 3 hours of program material may be recorded on a single 14 in. reel. Input and output video of the recorder may be monitored on the 14 in. picture monitor and oscilloscope waveform monitor located in the monitor bridge above the recorder. Input and output audio may be monitored by means of the audio amplifier/speaker in the monitor bridge.

An editor in the VR-1100 allows electronic editing and inserts at any point on the tape at tape speeds of 15 and 7.5 ips.

The film chain consists of an Ampex/Marconi 321 vidicon camera mounted in a Dage film chain housing with an integral prism multiplexer that permits the use of one TV camera to pick slide and film projectors. The Dage housing was modified from its original two unit configuration to a single unit configuration, with the slide projector, film projector and TV camera all mounted to the same frame. Critical physical alignment between the three units is thus retained during the vibrations and stress typical of a mobile unit.

The Bell & Howell 614 film projector, with 14 in. reel capacity and both magnetic and optical soundtrack pickup heads, provides a method of transferring previously made training films to video tape. A local control panel is located in the skirt directly below the projector.

The Spindler Sauppe Model 332 slide projector has a 32 slide capacity. Alternate operation of the turrets and two light sources permits changing from slide to slide instantly. Local and remote control at the video control console is provided for both the film and slide projectors. A 17 in. Conrac monitor for the film chain monitor in the video control console allows the video operator to see what is on the film chain, as well as have full control by means of the remote control panel.

Audio Control Area

This consists of an Ampex AG-350 full track audio recorder, a Dynamote 70 audio mixer, Gates turntable, two Vega wireless microphone receivers, and an Ampex speaker. Record and tape storage is beneath the turn table.

Intercommunication

Operating personnel inside or outside the van use an Ampex intercom unit located in the camera interconnect box in the center racks. Outlets are provided on each of the three cameras, at the audio control position video control position, film chain position and video tape recorder. Western Electric headsets with boom mikes are employed at each position.

Electrical System

The tractor-mounted 25 kw Onan electric power plant furnishes all the 120/240 v single phase power required when land-line power is not available. The AC power panel, over the forward workbench, provides central control. A power changeover switch box, on the front of the van under the power input receptacle, selects land-line or Onan power plant, as well as offering an air conditioning safety power disconnect switch.

Inside the forward lower storage cabinets are two Superior Electric Stabeline voltage regulators to help stabilize variations in land-line power. The air conditioner air return duct permits airflow over the regulators for cooling. When using generator power, the power changeover switch bypasses the van regulators ti avoid interaction with these regulators and the...