= NT/N. This decrease means that the as given by (1.18) is allowed to increase by N. By means of a numerical example, the net effect can be judged. Postulating the 125-channel PB-FBC found in Tables 1.2 and 1.3, suppose that N = 10. The required SIN is found to be 2 dB higher than that required by the wideband energy detector! (As a point of reference, replacing NT by NPN = 105 in (1.21), then making use of Figure 1.8, the optimum multichannel detector still requires 10.1 dB less SIN than the wideband radiometer.) A general conclusion drawn from this single example is misleading, how- ever. A second example will illustrate that PN spreading of the individual hop frequencies could decrease rather than increase covertness. Suppose that, relative to the ongoing example, the hop rate Rh is reduced by a factor of 20 with all other parameters remaining the same. Then the pertinent sys- tem parameters established by the communication are now: NT=2 x 10 Nh = 400 hops. The communicator now has two options in terms of signal design: pure FH or FH/PN. With pure FH, if the interceptor wishes to build a minimum channel PB- FBC, he will have to implement NTN = 50,000 channels. Such is probably unjustifiable, SO the interceptor opts for the wideband energy detector, which requires the same S/N° as before. Alternatively, assume that the communicator selects FH/PN with a PN code rate such that N = 101. Then, NPN = 2000, meaning that the intercep- tor could either implement a 2000-channel full-band FBC or a 5-channel minimum-channel PB-FBC (certainly affordable!). The SIN requirements for these two FBCs are, respectively, 5.3 dB and 2.7 dB below that of the wideband energy detector. Thus, the interceptor, by virtue of either choice (or any between), is able to better his performance over that of the wide- band energy detector. so, for this example, the communicator is seen to lose covertness by selecting FH/PN over pure FH. Of course, it must be conceded that the communicator could be forced to the FH/PN position simply because of