This is an interim report describing the changes in resonant response characteristics which occurred in developmental models of the AN/ARR-15 (XN-1) submitted by Collins Radio Company, Cedar Rapids, Iowa and (XN-2) submitted by the Radio Corporation of America, Camden, New Jersey, aircraft communications receivers as a result of exposure to service conditions. The test cycle included changes in ambient temperature from -30.C to +50.C and exposure to 95% relative humidity at 50.C for 48 hours. The test procedure used to evaluate changes in resonant response is described in detail. Data obtained from ten tests on six separate receivers (several receivers were run more than once) indicate that neither the (XN-1) nor the (XN-2) equipments meet the specification, (reference (b) paragraph £7n) which limits overall shift of resonant frequency to 0.03%. Modification of both receivers to reduce the amount of frequency shift under service conditions and revision of the method of specifying the allowable limits of overall resonant frequency shift are recommended.
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