a serious problem. The fact that the noise level must be measured in the absence of signal means that whatever time is taken to accomplish this must be taken from the time available to detect the signal. Switched (Dicke)-type receivers [7] work in this manner by providing a pre- cision noise source which is periodically switched into the receiver in place of the antenna signal and multiplexing the calibration noise and actual signal- plus-noise out of the detector between a noise-level measuring integrator Interception Detectors and the signal detection integrator. Typically, the performance penalty paid due to a 50 percent signal duty cycle and front-end switch insertion loss is about 4 dB in required S/N which clearly impairs the interceptor's detec- tion capability. What then are the possible detector and receiving system alternatives which minimize these disadvantages? One solution would be to continuously measure the received system noise in a band immediately outside of Wss, or to measure noise in a narrowband segment of Wss for which Phit is sufficiently small that an occasional signal pulse will have no significant effect on the measurement. This approach overcomes, to some extent, the problems with the switched (Dicke) method but suffers primarily from the fact that the measurement does not truly characterize the external and internal conditions over the whole bandwidth Wss. Therefore, more than acceptable error in set- ting the threshold is probable. In order to provide a means of wideband calibration without incurring the basic switched (Dicke) receiver losses, conventional temperature-measuring radiometers often employ switched parallel channels (e.g., Graham's receiver). Unfortunately, this technique, which is basically a differencing-null method, is inappropriate to the very wideband receivers of the type needed for intercept signal detectors because (1) uniform gain and phase-matching of the channels is very difficult, and (2) the form of the detected signal is not suited to separation into the nec