The authors discuss several designs for self-steering array combiners together with a simple frequency-offset tagging method which permits locking of combiner to one of several cochannel but spatially separate signals. The combiners use the output signal as a reference for extraction of phase information from each individual element-signal, thereby utilizing the full transmitted signal for element phase measurement. Designed for receiving PSK signals, the combiner inherently provides, as part of its design, the CW signal required for coherent demodulation of the combined array output. Laboratory measurements made with a four-branch combiner for two-phase PSK signals demonstrate the salient features of the combiner.

We discuss a possible method for interference control in radio systems whose desired signal is analog FM. The method utilizes the fact that the desired signal has a nearly constant envelope; with interference present, the composite envelope becomes noisy. A controlling processor measures this additional envelope noise, and iteratively adjusts the complex combining gain of an auxiliary signal to minimize the interference. The expected residual interference remaining after minimization is proportional to the reciprocal of the square of the rms envelope fluctuation of the desired signal. This result was confirmed in a laboratory simulation of an intersecting radio route case using both large and small index FM. Beginning with signal-to-interference ratios of 30 to 40 dB, the controller increased these numbers to about 60 dB, the expected theoretical limit for a signal with 0.1 percent rms envelope fluctuation.

We describe exploratory work designed to demonstrate the feasibility of directly interfacing terrestrial digital carrier systems to digital satellite systems. Designed to accept up to 30 T1 carrier systems on the terrestrial side, the interface is designed as a common-control, bus-oriented time-division switch using a common time-slot interchanger for simultaneous switching of up- and down-links. The output bit rate is about 50 Mbits/s. The controller is implemented as two Motorola M6800 microcomputer chips and associated memory. The switch can communicate with a variety of terrestrial originating switches, including those using either register-sender or cut-through operation. By proper software, a simultaneous mix of such originating switches can be handled, and either delay-start dial, wink-start or dialtone start outpulse control can be used in either direction of call setup (i.e., to or from a terrestrial switch connected to the satellite earth station).

Using simulated Rayleigh-fading FM signals, the baseband performance of a diversity system that uses a separate pilot is studied. The effect of various RF/audio bandwidth expansion ratios is included. These results show an approach to a constant asymptotic baseband SNR for large expansion ratios, with diversity increasing this asymptote by 5 dB in the case of moderate to large interference and/or RF noise levels (9 to 15 dB below the carrier), to over 10 dB in the case of lower impairment levels (21 to 27 dB below the signal level). Assuming the usual hex-cell radio coverage plan, and a propagation law of the formr^{-n}, n = 3or 4, bandwidth expansion ratios of about three to six seem to yield the most efficient RF spectrum utilization in many practical situations. The number of required channel subsets (cells) is strongly influenced by the propagation law ranging from about 19 forn = 3, to about 7 forn = 4.