Multitone Electronics Plc

Alexander P Lax

William R Barker

In a decoder suitable for use in a paging receiver of the type responsive to a transmission which includes a preamble sequence followed by batches each containing a synchronization word followed by a plurality of address and/or message words, the decoder is operative to detect a single synchronization word. Thereafter, the decoder is powered up to search in its specific frame in each batch by means of a clock which has been synchronized with the transmission and which provides the timing for searching in the specific frame of all subsequent batches. The clock may have coarse and fine modes of timing control, the coarse mode being applicable when initial bit synchronization is being attained, and the fine mode being applied subsequently to reduce the risk of the clock drifting out of synchronization.

Decoding arrangements for synchronous receivers

An FM demodulator includes frequency conversion means (20) to derive from an FM input signal (10) a pair of like signals that are mutually phase-displaced by 90.degree.. Such signals are filtered (26,28), squared (30,32) and sampled (38). The output signal (40) of the sampling means (38) is used to control (62) the local oscillator (16) of the frequency conversion means (20). In one arrangement, the magnitude of the control applied to the oscillator (16) is dependent on the frequency of one of the squared (30) signals, whereas the direction is dependent on the logic state of the output signal (40). A similar control method can be applied to a superheterodyne receiver.

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Alexander P Lax