A simplex radio transmitting and receiving apparatus, has a transmission blocking means which prevents selection of the transmitting mode of the apparatus if a signal of predetermined strength is being received by the apparatus at the time the press-to-talk key is operated. An over-ride circuit enables the blocking means to be disabled in an emergency or if another transmitter has been left operating in error. The over-ride circuit can be activated by, for example, repeated operation of the press-to-talk key, and ceases to operate when the key is released to return the apparatus to its receiving mode. Also disclosed is a transmission control means which can be used to modify existing transceivers to operate in accordance with the invention. In a further feature of the invention, means are provided to detect the higher power consumption of the transceiver in the transmit mode and thereby to give a warning of an unduly extended transmission, e.g. by faulty equipment.
CROSS REFERENCE TO A RELATED APPLICATION
This application is a continuation-in-part application of application Ser. No. 482 507, filed on Apr. 6, 1983, now abandoned, which is a continuation application under Rule 1.62 of application Ser. No. 296 181, filed on Aug. 25, 1981 now abandoned.
A simplex radio-accessories interface connector (30) connects the simplex radio (10) having a speaker amplifier (102) and a push-to-talk (PTT) detector (103) to accessories which include an earpiece speaker (107) and a PTT switch (110). The connector (30) has a first connector mating assembly (25a-d and 84a-d) for coupling the connector (30) to the radio (10) and a second connector mating assembly (44a-c and 48a-c) for coupling the connector (30) to the accessories. Inside the connector (30), a receive audio line (104a) couples the speaker amplifier (102) to the earpiece speaker (107) and a PTT detect line (122) couples the PTT detector (103) to the PTT switch (110). At the second connector mating assembly (44a-c and 48a-c), the receive audio (104a) and the PTT detect (122) lines are combined (44a and 48a).
Simultaneous transmitter operation in a radio network is prevented by monitoring the signal received at the control position from the transmitter of the apparatus, this signal being delayed by the passage down land lines connecting the control position to its transmission antenna and the receiver to its control position. If a signal is received within a known time period from the time of commencement of a transmit action then it is assumed to be a signal from a remote transmitter and the operation of the local transmitter is aborted to prevent interference. The system is particularly useful where land lines and consequent time delays are present between the control position and the transmitter and the receiver and the control position.
A method for realizing a group call in a digital radio network wherein a plurality of mobile subscribers participating in the group call roam within the area of at least one base station. Subscribers participating in the group call are guided one by one to talk on the same radio channel. To be able to handle the traffic in a controlled manner at all times without the subscribers congesting the radio channel by talking simultaneously, the base station is informed of the subscriber's desire to speak after the respective subscriber has indicated his or her desire to speak with predetermined signalling, the next speaker is selected at the base station on the basis of a predetermined algorithm, and the base station transmits an indication of a turn to speak to the subscriber which at the time is the next speaker.
A two-way radio includes a receiver having a squelch circuit and a selective calling decoder. A transmitter is connected to an inhibit circuit. The inhibit circuit is responsive to the selective calling decoder for permitting transmission after reception of the radio's ID code. The inhibit circuit inhibits further transmissions if the squelch circuit indicates loss of carrier for more than a predetermined time during receive.
A microphone circuit for a mobile telephone is capable of operations in either of two modes, i.e. in a hands-free or a push-to-talk mode. A constant current circuit is coupled in parallel with the microphone to preclude a change in a DC bias voltage responsive to switch operations, especially in a push-to-talk mode. A voltage comparator compares the bias voltage with a reference to detect control signals and selects a preferred mode of operation.
