Hitachi Denshi Kabushiki Kaisha

Tohoku Electric Power Company, Inc.

Fuji-tekku Kabushiki Kaisha

Mitsuo Shiraishi

Sakari Ohira

Fujio Sumi

Osamu Suzuki

Kenichi Suzuki

Yoshihiro Iwata

Kazuo Suzuka

A communication system for performing bidirectional communications substantially simultaneously between a telephone line and a radio communication system by using a single-frequency carrier. A base station includes a first radio transceiver and a line connector disposed between the first radio transceiver and the telephone line. A terminal station includes a second radio transceiver. Each of the first and second radio transceivers has a control unit, a transmitter unit including a signal compressor, a synchronizing signal generator and a modulator, and a receiver unit including a signal expander. The control unit sets the line connector to an interconnecting state in response to a connection request signal from the telephone line or the terminal station, while establishes a communication enabling state between the telephone line and the terminal station during a connection processing period. After the communication enabling state has been set up, a speech enabling state is established between the telephone line and the terminal station. The connection processing period is changed over to a speech period after the communication enable state has been established, to thereby allow communication between the telephone line and the terminal station.

Communication system interconnecting telephone line and single-frequency

A time-divisional duplex radio communication apparatus includes the steps of adding an interrupt enable signal to the compressed voice signal in place of the time-divisional synchronizing signal at a predetermined period in a radio communication apparatus served as a calling station, functioning the period corresponding to the time-divisional synchronizing signal as a reception period without having to add the time-divisional synchronizing signal to the compressed voice signal at the next transmission period if the interrupt enable signal from the calling station is received in a radio communication apparatus served as the called station, generating the interrupt request signal a predetermined time later than the reception of the interrupt enable signal of the calling station and transmitting the interrupt request signal in the reception periods of the calling station and the called station in a radio communication apparatus served as an interrupting station, indicating occurrence of an interrupt in response to the reception of the interrupt request signal in the radio communication apparatuses served as the calling station and the called station.

Radio communication method and apparatus which adds an interrupt enable

A radio relay communication system wherein a signal transmitted from active one of a plurality of radio units is received and recorded. When the transmission operation of the particular radio unit stops, the recorded signal is reproduced and transmitted by a relay unit, and another radio unit receives the signal from the relay unit. A relay start signal is transmitted from the first radio unit. and is received by the relay unit. In response to the relay start signal, the relay unit generates a sync signal of predetermined period. The first radio unit, in accordance with the reception of the sync signal, transmits an input signal as compressed to less than one half along the time axis. The relay unit alternates between the period of receiving the compressed signal and the period of transmission in synchronism with the sync signal. The compressed signal transmitted from the relay unit during the transmission period is received by the second radio unit and expanded along the time axis thereby to reproduce the input signal.

Radio relay method, radio relay system using the method and radio unit

A radio apparatus having a unit for receiving a first signal from a first transceiver compressed in time by a predetermined rate, a unit for reproducing a first original signal from the first signal, a unit for receiving a second signal from a second transceiver compressed by the predetermined rate during the reception period of the first transceiver, a unit for reproducing a second original signal from the second signal, and a unit for adding the first and second original signals and outputting the added signal.

Radio apparatus for simulataneously transmitting and receiving signals

A squelch circuit for a radio transmitter/receiver includes an amplifier, a digitally-controlled electronic volume control, a volume adjusting variable resistor, and a volume controller. The amplifier amplifies a received audio signal input and provides the received audio signal to a loudspeaker. The digitally-controlled electronic volume control changes the output level of the amplifier. The volume adjusting variable resistor outputs data representing a volume value. The volume controller constantly detects changes in volume value data output from the variable resistor, and controls an attenuation amount of the digitally-controlled electronic volume control in accordance with the volume value represented by the variable resistor. While in a 'mute' state, this volume control continues until a predetermined time has elapsed since the detection of the change in volume value data. The volume controller then sets the attenuation amount of the digitally-controlled electronic volume control to an infinite attenuation amount.

Squelch circuit for volume control of a radio transmitter and receiver

An automatic adjustment radio apparatus includes a transfer destination selecting unit and a data transfer unit. The transfer destination selecting unit selects a transfer destination of data set by a channel switch. The data transfer unit transfers the data set by the channel switch to a specific electronic volume and a specific address of a non-volatile memory selected by the transfer destination selecting unit. The data set by the channel switch is used as data to be set in the electronic volume and to be stored in the non-volatile memory upon adjustment.

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Musashino, Japan

Mitsuo Shiraishi