In a radio communication apparatus in which an audible tone is generated (21-22) in response to reception (15-17, 19) of either a primary or a secondary call signal and stopped by a reset switch (23), the audible tone is stopped (172, 18) when the secondary call signal is received. When the primary call signal is received, the audible tone is not stopped unless the reset switch is continuously closed during a predetermined time interval. Alternatively, the audible tone is stopped when the reset switch is twice closed although the audible tone is produced again after the audible tone is stopped when the reset switch is once closed. As a further alternative, the audible tone is stopped in response to repeated closure of the reset switch without being again produced when the reset switch is once closed.

A portable unit that may be called from a base station through a radio control channel by a succession of terminating call signals that is sent through the control channel from the base station to the portable unit for a first or restricted time duration (T.sub.1), selected in consideration of a battery saving period of a battery saving operation carried out in the portable unit. Within the battery saving period, the portable unit is put into transient active and inactive states during a first time interval and a second time interval, respectively. Selection is made so that the first time duration is longer than the second time interval to receive at least one of the terminating call signals within the first time duration in the portable unit. The base station monitors an acknowledgement signal for a second time duration (T.sub.2) after the lapse of the first time duration and interrupts the control channel when the acknowledgement signal is not received within the first and the second time durations. In the portable unit, the battery saving operation is released when the presence of the terminating call signals is detected by a squelch circuit.

A selective calling radio paging receiver includes a battery saving controller which activates the high power drain unit of the receiver at periodic intervals for allowing the detection of a preamble contained in a received digital paging signal and deactivates it for a period longer than the period of activation for power savings purposes. The power saving is disabled in response to the detection of a preamble for continued power activation to permit a sync detector and an address detector to be operated in succession. A window pulse is generated in synchronism with the clock timing of the received digital signal so that its binary level transition is time coincident with each window pulse. If noise occurs in the received signal, binary level transitions occurs which are out of coincidence with window pulses. The time-coincident binary level transitions and the noncoincident binary level transitions are counted to give first and second counts, respectively. If a valid preamble is lost or corrupted and if the first count is greater than the second, a valid indication of the received signal will be given and power activation is continued to operate the sync and address detectors in succession.

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.

A receiver receives a transmitted signal having a periodic predetermined signal, a method and apparatus detects a first predetermined signal. Power may be conserved during a portion of a subsequent predetermined signal. The subsequent predetermined signal is divided into at least a first and second portion. If the first portion is detected, the subsequent predetermined signal is considered detected and power is conserved for the second portion. If the first portion is not detected, the receiver remains active for the second portion in order to detect the subsequent predetermined signal.