Pulse Echo Pattern Analyzer

The report presents an original design of an instrument called a Pulse Echo Pattern Analyzer (PEPA). Its main function is to automatically determine the 'best' time constant of an exponentially decaying high frequency signal. The Pulse Echo Pattern (PEP) input signal can be either pulsed continuous, unipolar or bipolar. The carrier frequency and echo pulse width of the PEP are limited to 50 MHz and 200ns respectively. The time constant of the PEP is presented as a positive pulse whose width is equal to the time constant and is continuously updated in a manner that will average short duration perturbations while recording long term changes. The instrument measures the TC to an accuracy of plus or minus 2.5% and responds to time constant changes of 0.3%. Operation of the PEPA can be described as a digitially controlled analog processor. The time constant is obtained by sampling an internally generated exponentially decaying signal. This signal, called the reference exponential, is automatically adjusted to have a time constant representing a best fit to the input. Automatic adjustment of this time constant is accomplished by a feedback loop which acts to force the difference between the PEP and reference exponential to zero. The instrument can determine the time constant for a portion of the PEP as well as for all of it. (Author)