Abstract: A power amplifier suitable for use in TDD and TDMA systems in which burst transmissions have to conform to a time mask, comprises a power amplifier (10) having a signal input (11), a signal output (14) and a control voltage input (24). A r.f.feedback control loop is coupled between the signal output (14) and the control voltage input (24). The control loop includes detection means (18) coupled to a comparison means (22) in which the detected signal is compared with reference pulses produced by a generating means (28). The output of the comparison means is coupled to the control voltage input (24). In order to provide a control signal when the output power level is too low to be detected, an artificial detector (38) is connected between the output of the comparison means (22) and its input for the detected signal in order to feed back the control voltage. As a result the control voltage versus power output characteristic is extended which leads to the generation of less transient sidebands and interference.

Abstract: In FM transmitters, particularly land mobile FM transmitters, wherein a speech signal is pre-emphasized between 300 Hz and 3 kHz, whereafter it is filtered to provide a sharp cut-off and wherein the maximum peak frequency deviation is limited in order to maintain channel integrity, the level of undistorted speech can be raised to within 90% of the transmitter peak deviation by directly connecting an amplitude limiter to a filter amplifier which behaves as a level sensitive filter when the speech signal has been limited and prevents ringing and overshoot from occurring. The output from the filter amplifier is coupled to a low pass filter, typically a fourth-order Butterworth filter, via an attenuator which reduces the amplitude of the signal to prevent the onset of further clipping.