The ROBOT Model 400 converts picture information in the format standard with conventional TV to or from the format widely adopted around the world for slow scan TV (SSTV). The Model 400 performs this conver-sion in either direction . .
from conventional fast-scan TV to SSTV, or from SSTV to conventional fast-scan TV.
The main advantage in converting from TV to SSTV and vice versa is that doing so makes it possible to trans-mit and receive pictures over voice-grade communica-tion links such as the radio. Voice-grade channels, be-cause of their narrow
bandwidth, can carry signals all over the world at low tost. Conventional TV, requiring video bandwidth, is generally restricted primarily to line-of-sight communication distantes.
The main restriction in sending pictures over voice-grade channels is that a relatively long time must be taken to convey each new picture. Whereas conven-tional TV sends many frames per second, making it possible to create the illusion of
motion, SSTV requires many seconds to convey each new picture. The result is a sequence of "stills" of frozen pictures in succession.
By converting to or from TV standards, the Model 400 eliminates the need for special SSTV video equipment.
The Model 400 can accept signals from any standard broadcast TV camera, CCTV camera, home TV cam¬era or video tape recorder, and produce TV video sig-nals that can be viewed on any CCTV monitor.
Some features of the scan-converter are:
DISPLAY — Received SSTV pictures can be displayed on a TV monitor of any size display, black-and-white or color.
FREEZE MOTION — The Model 400 snatches one-field pictures from a TV camera or other video source either automatically at the beginning of each SSTV pic¬ture or upoii push-button command, thus "freezing" motion in
1/60 second.
PRECISION PICTURE REPRODUCTION — The Model 400 quantizes the video picture to 16 gray shades by means of a precision (1%) Analog-to-Digital converter. The TV picture can be viewed quantized in the same fashion before storage. Once in digital storage, the picture converted by a precision (1%) Digital-to-Analog converter to SSTV for transmission on the radio is thus an exact reproduction of the picture viewed on the TV monitor.
BUILT-IN GRAY SCALE GENERATOR — A built-in gray scale generator provides an easy to use standard for accurate setting of all video controls.
VIDEO INDICATOR — A video indicator lamp lights whenever the TRANSMIT SELECT switch is in a posi-tion which would apply video to the TRANSMITTER jack on the rear panel. This helps the operator from mistakenly transmitting SSTV video.
BUILT-IN STATION FUNCTIONS All of the switches, jacks and wiring needed to integrate SSTV into an exist-ing communication station are included in the Model 400 Scan Converter.
SOLID STATE CONSTRUCTION — All elements in the Model 400 are solid state. This eliminates the need to compensate for tube "drift" with front panel control settings.
PICTURE STORAGE — You are able to see a picture that takes 8 seconds to transmit only if there is some method of storing the slowly incoming picture elements so they can be displayed simultaneously to the eye. An SSTV picture is composed of 128 lines and 128 dots along each line or 16,384 resolvable picture elements. In addition, for digital storage, each picture element re-quires some number of binary bits to represent gray shades. In the Model 400, four binary bits at each picture cell represent anyone of 16 gray shades for each picture element value. Total binary storage is thus 4 x 16,384 or 65,536 binary bits.
The Model 400 employs dynamic 4K Random Access Memories (RAM's) for storage. There are 16 RAM's in the Model 400, each storing 4,096 binary bits. The memory locations in these RAM's are accessed at high speed to provide TV display and TV frame-freeze func-tions, and at low speed to correspond to the Blower rates of incoming or outgoing SSTV signals.
SSTV SIGNALS — The SSTV signal generated by thc Model 400 can be received by any standard SSTV monitor, such as the ROBOT Model 70A, 70B, 70C, or 70D. It may also be recorded on any audio tape recorder, cassette or reel. The Model 400 can also receive and display any standard SSTV signal generated by an SSTV sampling camera (non-freeze motion) such as the ROBOT Model 80A, or a previously recorded SSTV picture played back on any audio tape recorder.
The output spectrum generated by the Model 400 con-tains frequenties in the band between 1200 Hz and 2300 Hz. This audio range is readily pasled by the stan-dard dial telephone network, and by various radio transmitters employing SSB, AM or FM modulation.
The ROBOT Model 400, plus suitable conventional TV monitor and TV camera, is the only equipment needed to outfit an existing communication link for picture transmission and reception. Addition of SSTV does not disturb the use of the facility for voice communication; however, voice and SSTV cannot be transmitted simultaneously over the same channel.
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