Abstract :
This is an FM system designed specifically to record data aboard an aircraft under flight test and process the data to an acceptable and highly accurate form with reduction equipment located at a ground station. No telemetering link is required. Magnetic tape is the storage medium. The data outputs are time correlated. FM information is recorded on a 30 track, 3,000 ft. 1 1/2″ magnetic tape for a maximum of 40 minutes per reel. 25 tracks are used for data, which includes a voice channel. 4 tracks are used for reference signals for error correction, for timing and calibration markers, and for addressing the data on the tape with real time coding. 1 track is a spare. Commercially available FM modulators of the resistance bridge controlled, voltage controlled or inductance controlled variety may be used with carrier frequencies at the RDB channels 8 to 13. As many as 6 carriers may be multiplexed onto each tape track. Standard inputs are used to calibrate the airborne modulators. The ground reduction system uses the calibration information to automatically correct errors due to zero drift and sensitivity changes in system components. The ground system also corrects errors due to changes of tape velocity, commonly termed wow and flutter, by both mechanical and electronic devices. Function generators provide a means for correcting non-linear transducer curves to linear outputs. 24 demodulators and an audio channel will produce outputs for each playback pass of the tape. The demodulator outputs will drive oscillographs or strip chart recorders directly. At the same time, any one output may be fed to an analog to digital converter. The converter will digitize up to 1,000 samples per second and store the digitized information on an IBM 727 tape memory in a binary pattern suitable as a direct input to an IBM 704 computer. The data outputs from the demodulators are correlated in time to give a true indication of the time relationship of the signal inputs. Real time a- dresses are on the tape every 10 seconds and the playback of the tape readout can be programmed by using the addresses to start and stop the tape under search or read modes of operation. The tape readout may be started at any second interval. Readout over a particular section of tape may be repeated by selecting a REPEAT operating function.
