Robot 70 The model 70 monitor was the first commercially available slow scan unit in the world. The final version, the 70D, was quite sophisticated for a unit built around a P7 phosphor cathode ray tube. The 70 series are receive only monitors, but include in their circuitry Power feeds for the 80 series slow-scan cameras to enable the operator to transmit as Model 70A monitor well. The received SSTV signal is processed and then fed to the CRT. The CRT is scanned by free-running timebases thus producing a raster at all times whether or not a picture is being received. Due to the persistence of the P7 phosphor tube (similar to those used in early radar equipment) the displayed picture remains on the screen for approximately 8 seconds, after which time it has to be refreshed because it fades out. The picture is best viewed in a darkened room, or by using a viewing hood to reduce the level of ambient light failing on the screen. The models 70C and 70D were the last produced in this series and the facilities they offered make them useful even in today’s shack. The specifications for these two models include: * Reception of 128 lines @ 8 seconds or 256 lines @ 34 seconds. Will also accept 2 and 4 second transmissions, the resulting pictures being quarter and half screen respectively. * Automatic sync threshold circuit accepts line sync pulses from 3 to 10ms and frame sync pulses from 30 to 90ms duration. This permits the monitor to receive pictures originating from tape storage, where the tape speed may vary causing frequency shift. * SSTV input 40mV to 10V into 1k. S/N ratio for a clear picture is 6dB. SSTV output suitable tor cassette tape recorder. * Horizontal hold control to allow reception of pictures from countries using 50 or 60 Hz supplies. * Contrast control to vary the amplitude of the SSTV applied to the CRT. Model 70D only. Robot 70D only: * Oscillator mode enabling accurate fine tuning of the incoming SSTV or for setting-up a slow-scan camera. * Viewfinder mode allowing the monitor to be used to preview the picture from the slow-scan camera, enabling rapid set-up of pictures for transmission. * (The 80 series slow-scan cameras have a fast-scan output for feeding into the monitor for this purpose.) * It is also worth noting that, not without some patience, 256 line 32 second pictures could be received on this unit. * Although the picture will have started to fade by the time the scan is completed, enough remains on the screen to be viewed. Robot 70 Accessories There are two main accessories used with 70 series monitors a slow-scan camera for transmit and a viewfinder. As previously noted the model 70D monitor has a built-in viewfinder, so only a camera is required to transmit "live" pictures. The models 80 and 8OA slow-scan cameras are powered from a 70 series monitor and they operate as sampling cameras, the picture initially being fast-scan generated from a standard vidicon tube. This fast-scan Picture is sampled within the camera at slow-scan rates thus producing an SSTV picture. Both pictures are fed to their Bee appropriate output sockets on the camera. The slow-scan picture produced is in the standard format of 8 second/128 lines. The audio FM output is variable to 2.5V P/P maximum into 1k. There are contrast and brightness controls to set the picture to the desired level and a beam control for optimum sharpness. On the model 80A quarter (2 second) and half (4 second) frame durations can also be selected. The fast-scan output is suitable for driving 60-series viewfinders or the model 70D monitor direct. The models 60 and 61 viewfinders provide a convenient fast-scan display of the picture from the 80 series cameras. The picture viewed is an exact replica of the SSTV picture transmitted, therefore accurate setting of grey level, etc., is possible. The model 60 has a 4 inch display whereas the 61 is 6.5 inch. The fast-scan rate of 3 kHz used produces a 180 line display (200 lines @ 60 Hz).