There is disclosed a radio frequency transmitter for use in a wireless security system, which can sense abnormal state occurred in an objective equipment, by monitoring both the abnormal state and voltage supplied thereto. The invention also transmits the radio frequency for a given short period so as to save the power. The transmitter for carrying out those objects includes an address unit 110 for designating a specific address having a plurality of bits according to each objective equipment; an encoder 120 for coding each bit of the specific address which is designated when an abnormal state is occurred and producing a specific code data in series; an RF transmitter 130 for modulating said specific code data into a radio frequency in form of analog signal and amplifying said data to be suitable for transmitting; a sensor 100 for sensing the abnormal state occurred to the objective equipment; a power source sensor 140 for sensing a state of battery supplying voltage source to the entire system, and providing a logic data to the encoder in response to the state of the battery; a system driver 150 for driving the radio frequency transmitter and the encoder in response to the output data of the sensor and the power source sensor; and a driving controller 160 for restricting within a given period the transmission of the radio frequency when the abnormal state is detected.

A battery-powered mobile communications unit for reception and transmission of signals in which the continued transmitter operation, following activation, is controlled in response to accurate detection of battery deterioration. The battery voltage is monitored by a reset circuit to detect any voltage drop that exceeds a predetermined threshold and a command unit responds to the reset circuit to turn the transmitter off as long as the battery voltage is below threshold and to turn the transmitter on when the battery voltage rises above threshold. The duration of the voltage drop is also measured to determine if the drop is instantaneous, due to interferences or extended due to a battery deterioration. If extended, the command unit will not turn the transmitter on, even though the reset circuit indicates a rise in battery voltage above threshold.

A burst control circuit for use in a TDMA communications system comprises a power amplifier having two separate control terminals. The circuits also comprises an ALC circuit for producing and supplying a level control signal to the first control terminal of the power amplifier to perform negative feedback operation and to keep the level of an output burst signal constant. The burst control circuit further comprises a waveform control circuit which generates in response to a burst timing signal a waveform control signal having gently sloped leading and trailing edges and supplies the waveform control signal to the second control terminal of the power amplifier to control the waveform of the output burst signal.

A radio telephone apparatus power-supplied with a battery comprises a power supply control means for controlling the battery so as to terminate power supply if the apparatus is not operated for a predetermined time period. The apparatus further comprises means for informing at least a user of the termination of power supply prior to the power being turned off.

An amplitude control system particularly suitable for an active antenna array includes a power detector for generating a power level signal representative of a level of radio frequency (RF) energy radiated by an antenna element, or groups of elements, in a phased antenna array. A reference signal corresponding to a desired value for the radiated level of RF energy is set by a control device, and the power level signal and the reference signal are compared with one another. Depending on the comparison result, an attenuator associated with an RF amplifier than drives the antenna elements, is adjusted to maintain the radiated RF energy at the desired value set at the control device.