A High Speed Technique for Testing Spacecraft Telemetry Systems

Present methods of automatically testing spacecraft PCM telemetry systems utilize a one or two channel decoding scheme in which channel inputs are programmed from a precision voltage source and the PCM output from each channel under test is observed or compared one data channel at a time to a reference word value. This method has the disadvantages of being time consuming, placing extreme requirements upon the precision voltage source in voltage accuracy and ambient noise, and failing to simulate realistic data configurations in the output serial PCM wavetrain. A high speed technique which overcomes these advantages establishes a reference PCM data train from a reference PCM system which is electrically identical to the PCM system under test and is synchronized bit by bit so that a real time comparison to the reference PCM data train may be made. Word identification is maintained to identify channel location of errors in the system under test. By this method eleven point channel accuracy testing of a Gemini type format of 240 channels can be reduced from the present 90 minutes to 27 seconds. Since both PCM data trains are synchronized sampling times of the A/D converters are precisely at the same point in time and since corresponding channels are driven from the same source an inaccuracy due to voltage programming or test set ambient noise on the data input line is nullified.