gle hit is to be adequate for detection, the Low Probability of Intercept Communications Table 1.2 PPB-FBC D SIN requirements; PD = 0.9, PFA= 10 : Number of AS/N° Relative to the Channels Full-Band FBC+ 1,000,000 1.125 : 104 10,000 0.045 +2.8 dB 1,000 +3.8 dB 5 X 10-4 0.536 +1.5 dB 2.88 X 10-4 +5.6 dB 1.25 X 10-4 +5.4 dB #Based on a hit-related probability of 0.9 (see text) + The second detection threshold l = 1 in all cases @Hit-related probability is 0.63 (see text) per-hop channel detection probability must be made equal to the overall detection probability, i.e., PI = PD. Thus, a detection probability of 0.9 will be achieved if a hit occurs, while the probability of no hits per message will be 0.368 for a 125-channel absolute minimum channel PB-FBC, and 0.1 for a PB-FBC that has 288 channels. Table 1.2 summarizes the DS/N requirements for the PB-FBC relative to the full-band FBC as a function of f. As can be seen, the cost is significant, especially for the 1000 or less channel PB-FBC, which represents the range of practical detectors. A summary of the relative performance of the various detector configu- rations discussed to this point appears in Table 1.3. What should be deduced is the gross complexity (as measured by the number of channels) versus the Table 1.3 Performance comparison of detector types using wideband radiometer as reference. Detector Number of Required Implementation Channels Notes Optimum Multichannel -11.1 dB Impractical because of large number of channels Full-Band Filter Bank Combiner -7.9 dB Impractical because of large number of channels -1.1 dB Partial-Band Filter - 3.4 dB Practical but quite complex Bank Combiner and costly to build using analog mechanization of the channels -2.5 dB Wideband Energy Simplest and least costly of all types to build Interception Detectors performance tradeoff. Taking, for example, the 500-channel PB-FBC as rep- resentative of the realizable multichannel class, it can be seen that its S/N° performance is 7.7 dB inferior to the optimum detector and only 3