Analyzer for Complex Electric Waves

The method of analysis here described had its origin in a circuit built by J. VV. Horton in 1917. This had a resistance coupled tuned circuit responsive to the component desired. Following the tuned circuit two stages of amplification were used to magnify the selected current. This current was then passed on to a third unit where it was rectified and measured by a D.C. meter. It was evaluated directly by 230 ANALYZER FOR COMPLEX ELECTRIC WAVES 231 noting the meter deflection and referring to calibrations of the analyzer which had been made with known input currents. This elementary form of measuring circuit was developed during the World W a r for the analysis of the sound waves encountered in listening devices used for the detection and location of submarines and torpedoes. It covered the range of audible frequencies and had sufficient sensitivity for its original purpose. It will be remembered that the first commercial application of multiplex transmission by means of carrier currents came almost simultaneously with the Armistice. The continued study of carrier systems found a useful tool in the current analyzer but placed considerably more rigorous requirements on its performance. These were met by the addition of a second tuned circuit and amplifier system, working from the output of the first, thus giving far greater selectivity than is obtainable in a single circuit. The presence of the multi-stage amplifier between the selective circuits facilitates tuning by avoiding interactions between the circuits.