| Summary: | On the basis of an extensive literary review and the proposed northern communication system's requirements, a theoretical design criterion is selected and a corresponding synthesis procedure is described for an optimum second order Frequency Compression Demodulator. Subsequent to this, the detailed design and construction together with extensive laboratory and field testing of this device is presented. From the laboratory investigation, it is concluded, that the experimental threshold behavior of the demodulator is in agreement with theoretical predictions. In addition, these tests have assisted in the clarification of various controversies associated with the optimum design of this type of feedback demodulator. A comparison of the Frequency Compression Demodulator and Phase Locked Detector has resulted in a further understanding of the latter, as well as an improvement in• its threshold performance; on the basis of this, it is concluded that the threshold extension of the frequency compression unit over that of a properly designed phase locked loop is not as significant as previously suspected. Therefore, from this point of view, both devices are nearly equally suited for northern communication purposes. However, the former appears to have advantages when the received carrier is disturbed by the propagating medium. Finally it is estimated that use of these feedback demodulators in the E-scatter link from Rankin Inlet, N.W.T. to Saskatoon, Saskatchewan would result in successful demodulation of a 10 Hz bandwidth it least 80 percent of the time if 500 watt transmitters are employed with the present antenna system. This research was supported by the National Research Council of Canada under Grant Nos. A-2193 and A-3382 and by the Institute for Northern Studies.
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