Abstract: An acknowledge back (ack-back) paging system is provided which includes a central station which transmits a group of message signals to a group of ack-back pagers which are addressed as a group. The users of the group of addressed ack-back pagers indicate a response to their respective pagers thus providing ack-back data. The pagers in the group of addressed ack-back pagers then simultaneously transmit back to the central station their ack-back data on different frequency sub-bands, a different frequency sub-band being allocated to each of the pagers in the group.

Abstract: A paging system is provided for transferring information to a paging receiver. The system includes a central controller having a paging controller, an encoder, and a first transmitter. The paging controller receives the information and data designating the paging receiver from an entry device. The encoder, in response to the data, generates a selective call paging signal designating the paging receiver. The selective call paging signal is transmitted to the paging receiver by the first transmitter. The paging receiver receives and decodes the selective call paging signal generating a control signal. A switching device is provided for selecting a normal and a deferred paging operating mode. In response to the control signal, a coded acknowledgment signal is generated indicating the selected paging receiver mode, and transmitted back to the paging controller by a second transmitter included in the paging receiver.

Abstract: An acknowledge back (ack-back) pager is provided for receiving paging signals from a central paging station. The central paging station transmits a group of message signals to a group of ack-back pagers which are addressed as a group. The users of the group of addressed ack-back pagers indicate a response to their respective pagers thus providing ack-back data. The pagers in the group of addressed ack-back pagers then simultaneously transmit back to the central station their ack-back data on different frequency sub-bands, a different frequency sub-band being dynamically allocated to each of the pagers in the group. Each ack-back pager determines whether the paging signals received thereby exhibits a signal level less than a predetermined threshold level. If the paging signals received by a particular ack-back pager exhibit a signal level less than such predetermined threshold level, then the pager transmits back to the central station at a first output power level.

Abstract: An improved electrodynamic acoustic transducer with a slotted piston suspension system which results in greater linear excursions by relieving stresses within the diaphragm during the movement and allows improved operations of transducer with greater magnet size and greater radiating areas of diaphragm suspension. Overall efficiency of transducer is thereby improved. An improved piston suspension can be utilized with electrodynamic acoustic transducers operating in the range of 200 to 20,000 cycles per second.

Abstract: A switching amplifier includes a pulse width modulator for converting a bipolar input signal, which may be a speech signal, into a train of unipolar pulses having durations which vary with the instantaneous absolute amplitude of the input signal. The pulses control the energizing of a series switch which supplies current to a switching bridge circuit. The switching arms of the bridge circuit are controlled by the polarity of the input signal. Another switch and several diodes are used to provide a path for output current when the series switch is open. The output current is filtered to remove fluctuations at the switching rate, and applied to a load. The amplified output voltage signal accurately follows the input signal, and the efficiency of conversion of DC power to AC output power can approach 100 percent, limited only by switching and filtering losses. A single polarity DC supply, such as a battery, is used to provide bipolar output current to an ungrounded load.

Abstract: An improved input/output transducer having an arrangement for changing the frequency response of a small speaker when it is used as a microphone provides optimum response for both requirements. When utilized as a microphone, most of the apertures in the speaker enclosure wall are covered by a movable grille and the remaining ones are appropriately damped. This provides an acceptable frequency response with lowered sensitivity. When used as a speaker, most of the enclosure apertures are completely clear, although a small number may remain damped, providing sufficient output in speaker mode.

Abstract: The permanent magnet of a magnetic structure is formed of isotropic magnetic material, and is magnetized along the path that the flux follows during use of the magnetic structure to increase the efficiency of the magnetic structure in use. The magnetic structure, which may be the annular magnetic structure of an electrodynamic loudspeaker, includes a cylindrical permanent magnet and an annular cup-like return path element connected to the magnet at one end thereof and forming an air gap with the magnet at the opposite end. Apparatus is provided for magnetizing the permanent magnet having an annular portion which may extend into the air gap of the speaker magnetic structure, to provide curved magnetic lines in the permanent magnet in substantially the path of the operating flux to the air gap.