Abstract: The present invention relates to a feed-forward amplifying device suitable for radio communication systems such as digital automobile telephone.

Abstract: A feedforward amplifier having a distortion detection loop and a distortion elimination loop is provided that achieves increased accuracy, improved response, and stable operation. A variable attenuator is placed in front of a detector in a loop output stage, and the amount of attenuation in the variable attenuator is set large during a transient response period during the rising of the amplifier, and set small during a steady-state condition. The detection of the transition to the steady-state condition is accomplished, for example, by comparing the detector output with a prescribed threshold value. The width of perturbation is set large during a transient response period, and set small during a steady-state condition.

Abstract: A phase angle .theta. of a received signal is calculated according to a formula .theta.=tan.sup.-1 (Q/I), where I and Q are magnitudes of baseband signals obtained by quadrature detection of the received signal. An angular velocity .DELTA..theta. of the phase angle .theta. is also calculated. A variance parameter .SIGMA..sigma..sup.2 is calculated from a deviation .sigma.=.DELTA..theta.-.DELTA..theta., where .DELTA..theta. is a moving average of the .DELTA..theta.. The variance parameter .SIGMA..sigma..sup.2 thus calculated, is compared with a reference value to determine if a burst signal exists. Since the determination is performed essentially based on a phase of the received signal and not on an amplitude of the received signal, fluctuation of the amplitude of the received signal does not affect the decision.

Abstract: Signals including two signals having levels different from each other are transmitted to the satellite, and the phase difference between the return signals of the two signals is measured. Transmission power control is performed so that the phase difference becomes equal to the difference measured in clear weather conditions.

Abstract: In a data communication system, such as an earth station for a satellite communication system, a level control unit enables control of an amplitude of a data signal which is reduced in a cable, regardless of the form of the data signal. The data communication system includes a first system including a unit for sending a continuous signal having a first frequency and a data signal having second frequency, a cable, and a second system for receiving both sent signals through the cable. The second system includes a unit for correcting an amplitude of the data signal on the basis of an amplitude of the continuous signal to a predetermined level. The second system may also include a unit for further correcting the amplitude of the data signal on the basis of the frequency difference between the data signal and continuous signal, so that the amplitude is adjusted at the second frequency.

Abstract: A radio receiver demodulation system which utilizes a sweep track type phase lock circuit and provides stable demodulation by starting and stopping the sweep on the basis of a decoded code error.

Abstract: An automatic gain control (AGC) circuit has a first filter to which a received signal is applied, followed by a variable level adjusting circuit, for producing an automatic gain controlled signal. A feedback loop set up between the input and output of the variable level adjusting circuit, contains a second filter exhibiting a narrower equivalent noise band width than that of the first filter. The second filter responds a particular signal component having a predetermined frequency spectrum and a certain duration and performs an integration operation on the particular signal component.

Abstract: An automatic frequency control system for use in a frequency converter of a time division communication system, wherein the nonmodulated portion contained in the burst signal is selectively frequency discriminated. The frequency discriminated output is held for a certain period of time and then used as the oscillation frequency control signal of a local oscillating means.

Abstract: In the base-band carrier-recovery circuit used in the demodulator of radio equipment using a PSK modulated signal, a first doubled signal (sin 2.theta.) is obtained by using first and second outputs (sin .theta., cos .theta.) in-phase quadrature with each other from an in-phase quadrature detecting means. A second doubled signal (cos 2.theta.) having a phase difference of 90 degrees from the first doubled signal (sin 2.theta.) is obtained by fullwave rectifying the second output (cos .theta.) and transforming the output waveform. Thereafter a quadrupled signal (sin 4.theta.) is generated from the first and second doubled signals. The quadrupled signal is then fed back to a VCO via a loop filter, thereby recovering the reference carrier signal which is in phase with the received PSK modulated signal.