A wave analyzer employing variable speed magnetic tape

Abstract

The object of this thesis is to make a preliminary investigation of a type wave analyzer. The proposed wave analyzer would employ a variable speed magnetic tape to effect a multiplication in frequency. The resultant analysis would be made with a constant-percentage resolution. A basic analyzer theory baa bean formulated. Specific theoretical results include (1) determination of two multiplier speed-time relationships , a minimum-analysis-time solution, and an equal-analysis-sample solution, (2) determination of the required length of sample tape which is found to be a function of the desired percentage resolution, and (3) evaluation of the response of a simple selective network to a frequency excitation which varies very nearly linearly with time while within the pass-band. Dynamic amplitude and frequency distortion will occur as a result of the variable frequency excitation. It is shown that these analyzer errors can be predicted by use of a single parameter. An experimental investigation of the analyzer principles was attempted using magnetic tape wound around a disc. The speed of the disc was controlled by a Ward Leonard system. Other experiments were made with the speed of the disc slowing down due to its own damping. Experimental results were limited by: (1) variation in the distance between the reproduce head and the magnetic tape due to the eccentricity of the disc, and (2) inability to control accurately the speed of the disc. Within the pass-band the deviation from a linear sweep for both multiplier functions is less than l/Q. It is concluded that linear-frequency sweep theory is applicable to the proposed analyzer. Furthermore, it Is concluded that equal sample analysis is a desirable feature in order to avoid a possible time-distribution ambiguity in measurements. However, the required multiplication function unfavorably affects total analysis tins requirements and analyzer complexity.