Abstract: A digital signal error reduction apparatus of the present invention tracks and reduces both quickly changing errors and static errors in a digital signal which are caused by time variant multipath distortion, co-channel interference, and other transmission path interferences, including nonlinear distortion. A transversal filter is implemented for filtering the digital signal. A error detection device is implemented for calculating an error of the digital signal. A coefficient engine device is used for receiving the digital signal and the error, for extracting the error, and for updating a tap coefficient for the transversal filter so that the error is minimal.

Abstract: A demodulation apparatus of digital detection processing type of the invention offers versatility as consumer equipment in mobile communications, ATV, satellite broadcasting, CATV, and the like. A modulated wave output is obtained by multiplying an input digitally modulated wave signal by a local oscillating signal from a local oscillator. The obtained modulated wave output has a center frequency which is substantially equal to the symbol frequency. The modulated wave output is A/D converted at a rate which is four times as high as the symbol frequency, so as to be output as interleaved I and Q digital data. The I and Q data is split, and the split I and Q data are multiplied by coefficients of "+1" and "-1", respectively. The multiplied two output signals are selectively output. Thus, the data multiplied by the coefficients of "+1" and "-1" are alternately output for the I and Q signals, so as to perform the digital detection.

Abstract: At the transmitter side, carrier waves are modulated according to an input signal for producing relevant signal points in a signal space diagram. The input signal is divided into, two, first and second, data streams. The signal points are divided into signal point groups to which data of the first data stream are assigned. Also, data of the second data stream are assigned to the signal points of each signal point group. A difference in the transmission error rate between first and second data streams is developed by shifting the signal points to other positions in the space diagram expressed at least in the polar coordinate system. At the receiver side, the first and/or second data streams can be reconstructed from a received signal. In TV broadcast service, a TV signal is divided by a transmitter into low and high frequency band components which are designated as first and second data streams respectively.

Abstract: A forward error correcting transmitter and receiver for preventing the erroneous detection of synchronization is provided in a system in which synchronization of an interleaver circuit and a deinterleaver circuit, to be inserted between a convolutional encoder and a Viterbi decoder, is obtained from a synchronization detecting circuit of the Viterbi decoder. A LFSR (Linear Feedback Shift Register) is used as a row-direction address counter during writing and an up/down counter is used as a column-direction address counter during reading, during the interleaver circuit. In the deinterleaver circuit, an up/down counter is used as the column-direction address counter during writing, and an LFSR is used as the row-direction address counter during reading.

Abstract: In a television receiver in which image frequency signals for desired signals are removed when television broadcasting signals are frequency-converted through a local oscillator and mixers, the local oscillator generates biaxial orthogonal signals to be frequency-converted by respective mixers, an output signal of one mixer being phase-shifted to be added to an output signal of the other mixer so as to thereby offset only the image frequency signals. The local oscillator and a phase shifter operate so as to follow the frequency change of the intermediate frequency signal so as to thereby stabilize the suppression of the image frequency signal.

Abstract: Satellite transmission sometimes uses a method of modulating by a sub signal a subcarrier with a frequency set higher than that of a main signal and subjecting the main carrier to frequency modulation by the resulting baseband signal. This method is, however, accompanied by a problem of the occurrence of crosstalk from the main signal to the sub signal. This is attributable to the limited band width of the main carrier on the transmission line, allowing a correction signal equal in magnitude but negative in phase to the crosstalk to be easily prepared on the basis of the transmission line amplitude and group-delay frequency responses and the main signal. The crosstalk may be improved if this correction signal is prepared from the main signal on the transmitting side and added to the sub signal to be transmitted or if the correction signal is prepared from the demodulated main signal on the receiving side and added to the demodulated sub signal.

Abstract: A television signal receiving apparatus receives a new standard television broadcasting signal in an environment in which conventional standard television broadcasting signals are present. A first tuner coupled to a first antenna extracts a first television signal which contains a new standard television signal and a conventional standard television signal of the specific channel at a first ratio, and a second tuner coupled to a second antenna extracts a second television signal which contains the new standard television signal and the conventional standard television signal of the specific channel at a second ratio. In an operation unit, a multiplier multiples the second television signal by a predetermined coefficient, and a subtracter subtracts an output signal of the multiplier from the first television signal. An output signal of the subtracter becomes the new standard television signal when the coefficient has a specific value.

Abstract: Radio waves used in broadcasting and communications making use of broadcasting satellite and communication satellite are FM signals, and the frequency shift and exclusive bandwidth vary depending on the modulation signal. The satellite broadcasting receiver is designed to control the frequency shift so that the amplitude of the demodulation signal is constant, thereby making the bandwidth of the intermediate frequency filter, so as to be capable of receiving using just one filter. At this time, the frequency shift can be controlled continuously, from large to small one, in a predetermined exclusive bandwidth. When further expanding the frequency shift, since the exclusive bandwidth is extended, the noise electric power is increased and the receiving sensitivity is lowered as compared with the exclusive machine. Accordingly, when expanding the frequency shift, the noise bandwidth is narrowed in the PLL demodulator, thereby enhancing the receiving sensitivity.

Abstract: A signal of the same frequency band as an ordinary NTSC signal of the video signals is transmitted with the conventional frequency band but the other frequency components are frequency-converted to a frequency higher than the sound subcarrier as the multiplex signal. The ordinary video signal, sound subcarrier and multiplex signal are frequency-multiplexed and the main carrier is transmitted by angle modulation as the modulation signal. In this case, as the multiplex signal, a signal other than the ordinary signal may directly be frequency-multiplexed and the signal may be multiplexed. Using amplitude or angle modulation to improve the demodulation accuracy or S/N through the angle modulation. The ordinary signal is regenerated like in the conventional system, without influence on the conventional receiver. In addition, since the ordinary video signal and the multiplex signal are separated in the frequency band, these may be used as the independent new transmission bands.

Abstract: The invention relates to a television receiving tuner for receiving television signals of VHF band/UHF band, a CATV signal, and a satellite television broadcasting signal. As a circuit for receiving the television signals of the VHF band/UHF band and the CATV signal as a first input signal, there is provided a double super type tuner of the up/down converter system including a first local oscillator (6) and a first mixer (5) which construct an up converter and a second local oscillator (10) and a second mixer (9) which construct a down converter. When the satellite television broadcasting signal as a second input signal is received, the first local oscillator (6) and the first mixer (5) in the up converter section are switched by switching circuits (12, 13) and used as a down converter.

Abstract: There is provided a wide band transmission system which, by using two or more filters and gain control circuits, is operated so as to determine the gain control amount of the gain control circuits according to an intensity and frequency band of a signal which is desired to be received. Further, a bias circuit increases the attenuation amount of the gain control circuit connected to the filter whose pass band is out of the band of the desired signal.

Abstract: A signal receiver which is capable of receiving and demodulating a satellite broadcasting signal which is an FM signal and a terrestrial broadcasting signal which is an AM signal is disclosed. FM and AM signals are frequency-converted into signals having frequencies in a same intermediate frequency band by making common use of a radio frequency amplifier, a mixer, a local oscillator and an intermediate frequency filter. At the time of reception of an FM signal, the FM signal is demodulated in a phase-locked loop circuit, and a local oscillator is subjected to frequency modulation by a part of the demodulated signal, thereby constituting an FM negative feedback loop, and thus narrowing the occupied bandwidth of the FM signal. At the time of reception of an AM signal, the phase-locked loop circuit is used to regenerate a carrier, and the output signal of the phase-locked loop circuit is input to a multiplier to effect synchronous detection of the input signal.

Abstract: A high frequency amplifier circuit based on an amplifying transistor, e.g. a dual-gate FET, having an A.G.C. voltage applied to a control terminal thereof to control the transistor DC operating current, has a diode connected between an input electrode of the transistor and a source of an input high frequency signal. All or part of the DC operating current of the transistor is passed through the diode as the operating current of the diode to thereby produce a high degree of attenuation by the diode when the transistor current level is small, so that reduced cross modulation interference is produced by the transistor when a high degree of gain reduction is executed by A.G.C. control.

Abstract: A signal receiver generates a reference signal that sweeps frequencies of desired channel bands, and then feeds the reference signal to an input terminal of receiver unit via a signal-switching circuit that performs switching of the desired-channel signal and the reference signal. The signal receiver then detects the signal strength present in plural frequencies of intermediate frequencies delivered to an output terminal of the reference signal, and after storing detected signal data in a memory, the signal receiver compares the detected signal data to desired frequency characteristics. Then, the signal receiver determines tuning voltages of respective tuning circuits so that the differences which arose from the comparison can be minimized. After determining the tuning voltages, these voltages are delivered to respective tuning circuits, and then a switching operation between the reference signal and the desired channel signal is executed before the signal receiver eventually receives the switched signal.

Abstract: A frequency conversion apparatus for converting a high frequency signal into an intermediate frequency signal includes a mixer section for mixing a high frequency signal with a local oscillator signal so as to obtain an intermediate frequency signal, and an amplifier connected to the mixer section via a high frequency stopping circuit for supplying a constant direct current to the mixer section as a constant current source. A current flowing in the mixer section when the local oscillator signal is applied is kept substantially equal to a direct current flowing in the mixer section when no local oscillator signal is applied thereto. The amplifier is used for amplifying either the high frequency signal or the intermediate frequency signal, or both signals at the same time.