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exposed thin film resistance elements. Calibration channels used to monitor battery voltage and fixed resistance values will also provide a code for channel identification by a fixed sequence of a long burst followed by a short blank interval.This basic telemetry encoding system has been a custom design for this particular group of experiments and compatible operation with the radio tracking system. The basic 48-channel telemetering encoder weighs approximately 3.2 ounces and requires under 12 mw operating power (4 milliamperes at 2.7 volts). The low operating power permits continuous operation for a period in excess of three weeks with batteries weighing 2.8 ounces. The telemetering system occupies a printed circuit card 5y 2 inches in diameter and 3^ inches maximum height, as shown in Fig. 8. The entire assembly will be cast in plastic foam for satellite installation.For this installation, time-interval channels will lie between 5 and 30 milliseconds duration and high-frequency channels between 5 and 15 kc. These values have been dictated by considerations other than limitations in the telemetry encoder. The upper limit of the high-frequency channels was set by signal-to-noise considerations in this system which involves use of low transmitted power over long distances which necessitates narrow noise band-widths. The 5 kc lower limit for the high-frequency chart* nels was determined by frequency components in the signal which would introduce excessive errors in the radio tracking system. Similarly, extreme values for the time-interval channels were dictated by consideration of the maximum time allowable for scanning all channels and the minimum number of cycles in each burst to per mit accurate data extraction. With these system parameters, a complete scan of the 48-input channels will be made approximately twice each second. Laboratory tests on system reproducibility indicate that accuracy limitations will be determined by signal-tonoise ratio problems in the radio transmission link.The peak memory circuit and orbital switch are mounted on a single card identical in size to the telemetering encoder and weighs approximately 2.5 ounces. This unit is shown in Fig. 9.Precalculation of short-circuit currents is necessary in order to provide effective protection of power systems against possible short circuits. A

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