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The primary function of the Model 28 Automatic Send-Receive Set (ASR), is to serve as a complete high capacity message originating station for correspondence information and items of intelligence. The ASR is made up of a group of basic component units. These include a keyboard, page printer, tape punch and tape reader, electrical service unit and motor.
KEYBOARD: The Keyboard gives the Model 28 ASR centralized control for preparation and transmission of data. The keyboard is designed at an improved angle to facilitate operator output and efficiency. The keyboard arrangement is similar to a typewriter. The top bank of red keys is reserved for non-typing functions such as an automatic page printer paper feed out (“LOC LF”), carriage return (“LOC CR”),receive(places the asr in receive mode)("REC"), send(places asr in the transmit mode),("SEND"), break(opens the electrical loop)("BREAK"), back space (causes the tape punch to backup one character)("TAPE B.SP.") and a repeat key (repeats character typed from keyboard) (“REPT”). Typing and perforating functions originate from the operation of green color keys. Provision on the keyboard base is made for the page printer, motor unit and the tape punch unit. Rubber mounting gaskets tightly seal the keyboard against dust and assure quiet operation.
PAGE PRINTER: The printing principle features a type box. All type characters are contained in one lightweight, compact assembly. Overscoring and underscoring are eliminated since each charter is mounted on a separate pallet which allows for type alignment. The type box can be quickly removed without tools for cleaning. The featherweight carriage is built for speed. The printer can be operated in any position, assuring dependable operations on planes, ships and in all mobile units. Copy is more uniform because the same print hammer blow is applied to all characters. Straight course ribbon travel simplifies ribbon changing.
TAPE PUNCH: Tape punch can be configured to punch paper tape to perform storage and recording of information in 5-level coded tape. The tape punch is also referred to as a perforator or reperforator. The perforator may be used for the preparation of paper tape locally from the keyboard operation. The reperforator may be used for both tape preparation initiated locally or through signal reception. These units perforate standard 11/16-inch paper tape into 5-level chadless form.
ONLINE TAPE PUNCH: A reperforator is an auxiliary receiving-only typing unit that is mounted under the left-hand dome of the console. This unit receives incoming messages in printed tape form while the ASR’s primary tape punch unit is being used for tape preparation.
TAPE READER: The tape reader, also referred as a transmitter-distributor (TD), is the tape reading facility that controls the automatic transmission of messages. The tape reader unit readily accommodate fully perforated chadless 5-level 11/16-inch paper tape. Features of the unit with fixed sensing heads include a 3-position switch for “stop”, “start” and “freewheeling” – an aid to easy tape threading. A “tape out” pin detects the end of the tape and stops unit operation. Hinged tape lid has manual control. A tape guide on the unit keep tape in proper alignment.
ASR CONTROL SWITCH: In actual operation, the operator can select, by means of a control knob located to the left of the keyboard, any one of the three operating conditions to meet the communication need:
In the KEYBOARD (K) setting, the ASR keyboard can be used to transmit messages directly to another station. A record of the message is made available on the local page printer for monitoring.
In the KEYBOARD-TAPE (K-T) setting, the ASR keyboard can be used to perform dual operations of transmitting messages electrically while simultaneously perforating tape by mechanical means.
In the TAPE (T) setting, the ASR keyboard can be used for direct mechanical perforation of tape at speeds in excess of 100 WPM. In this setting, the page printer is available for receipt of incoming messages or to monitor transmission from the transmitter-distributor.
In addition to the functions available in the three settings of the ASR Control Switch, there are many other applications that are accomplished by changing the electrical circuitry, to accommodate specific needs. Of major importance is the “Line-Test” switch which provides for both “local” as well as “on-line” operation of the ASR.