Elimination of false-locking in long loop phase-locked receivers

Even though long-loop phase-locked techniques are finding increasing application in the fields of mobile radio and satellite communications, their use is not without drawbacks. Time delay associated with filtering processes within the loop causes a degradation in acquisition capability, and information components entering the control loop cause a reduction in adjacent channel performance. A split-loop technique is described here which eliminates false-locking, substantially improves the acquisition characteristics to that associated with a loop with zero time delay, and 'cleans up' the first local oscillator spectrum. It is also shown that the technique is simple to implement. The effect of excess time delay on the noise bandwidth of both a conventional and a split-loop receiver is investigated.