prediction will suffer. In general, a guide to bearing uncertainty is given by > degrees for a signal at crossover, but where SNR0 is the signal-to-noise ratio that would apply at boresight. To obtain more precise predictions at a given bearing, the actual S:N ratios of the signals of interest are used. (The results may be derived assuming that noise induced errors are approximated by relating differentials to uncorrelated noise). For adjacent processing using, say, Channel 1 and Channel 2, the bearing uncertainty (angle noise), Δø (rms), is given below. In these results, square-law detection is assumed and the SNR figures are for signals at video (baseband), for the bearing angle φ. rads where SNR1 and SNR2 are the video (base-band) signal-to-noise values for the channels for Antenna 1 and Antenna 2, when square-law detection is used. In the case of 3-channel processing, an expression which is applicable when the S:N ratios in all three channels exceeds unity (when ln(1 + 1/SNR) ≈ 1/SNR is true in all three channels), is where SNR1, SNR2 and SNR3 are the video signal-to-noise values for Channel 1, Channel 2, and Channel 3 respectively, for the bearing angle φ. A typical DF system with six antennas A schematic of a possible DF system, employing six antennas, is shown in the figure. The signals received by the antennas are first amplified by a low-noise preamplifier before detection by detector-log-video-amplifiers (DLVAs). The signal levels from the DLVAs are compared to determine the angle of arrival. By considering the signal levels on a logarithmic scale, as provided by the DLVAs, a large dynamic range is achieved and, in addition, the direction finding calculations are simplified when the main lobes of antenna patterns have a Gaussian characteristic, as shown earlier. A necessary part of the DF analysis is to identify the channel which contains the largest signal and this is achieved by means of a fast comparator circuit. In addition to the DF process, other properties of the signal may be investigated, such as pulse duration, frequency, pulse repetition frequency (PRF) and modulation characteristics. The comparator operation usually includes hysteresis, to avoid jitter in the selection process when the bearing of the incoming signal is such that two adjacent channels contain signals of similar amplitude. Often, the wideband amplifiers are protected from local high power sources (as on a ship) by input limiters and/or filters. Similarly the amplifiers