An oscillator is controlled so that it produces the correct frequency in the transmitting condition, and so that it produces a slightly different frequency in the receiving condition. This is achieved by a circuit which supplies a first control voltage to the oscillator for transmitting and which supplies a second and different control voltage to the oscillator for receiving. This second and different control voltage causes the oscillator frequency in the receiving condition to be different so that there is no interference to or improper operation of a repeater system. The circuit also prevents any modulation signals from reaching the oscillator in the receiving condition, thus preventing false signals or other problems.
A radio frequency switch includes a field-effect-transistor (FET) having a gate connected to a voltage multiplier. The control voltage for the switch is delivered to the voltage multiplier which delivers an increased gate voltage to turn the switch on. The voltage multiplier is driven by fluctuations of the control voltage as a transceiver, for example, is switched from the transmit to the receive mode.
After bit synchronization and frame synchronization are established in accordance with a transmission signal from a transmission office, reception RX is stopped until a reception timing assigned to a group of a portable radio unit comes. A receiving operation is performed again at the reception timing assigned to the group of the unit. If the ID code of the received signal coincides with the ID of the unit, an informing operation is performed. At the same time, transmission TX is performed. A transmitting operation is performed during a transmission signal stop period TXOF upon completion of transmission of data corresponding to all the eight groups. The transmission timing of the portable radio unit is based on the fact that frame synchronization is established in the reception RX, so that transmission TX is performed at a timing assigned to the group of the unit in the reception RX. The above-described timings prevent the transmission office and the portable radio unit from performing simultaneous transmission.
A radio frequency switch includes a field-effect-transistor (FET) having a gate connected to a voltage multiplier. The control voltage for the switch is delivered to the voltage multiplier which delivers an increased gate voltage to turn the switch on. The voltage multiplier is driven by fluctuations of the control voltage as a transceiver, for example, is switched from the transmit to the receive mode.
A transmitting and receiving apparatus suitable for use as a digital cellular type mobile station. The reference reception carrier frequency and the reference transmission carrier frequency are different. Signals are transmitted and received such that an offset frequency of a received signal of an actual reception carrier frequency relative to the reference reception carrier frequency is detected and multiplied with a signal of the reference transmission carrier frequency, and the multiplied output used as the transmitted signal of an actual transmission carrier frequency which follows the actual reception carrier frequency.
A time division duplex transceiver incorporating a dual conversion superheterodyne receiver, and in which the first receiver local oscillator doubles as the frequency source for the transmitter. The oscillator is a voltage controlled oscillator VCO forming part of a mixer-type phase locked loop. Frequency deviation in the loop is achieved by mixing the VCO output with a selected harmonic of the output of the second receiver local oscillator. The reference oscillator is a crystal controlled oscillator whose output is switched as between transmit mode and receive mode at a switch before being passed to the loop phase detector. The transceiver is able to rapidly and repeatedly alternate between transmit and receive modes and is thus well suited to time division multiplex operation.
