Abstract: A VSB modulator receives a stream of data at a 10.76 MHz constant symbol rate and converts it to a 6 MHz bandwidth signal centered at 44.0 MHz. The incoming data is interpolated by three to generate three data images and a digital filter selects the image embracing the range of 5.38 to 10.76 MHz. A sine X/X correction is added to compensate for the loss experienced in the D/A converter. The signal for the D/A converter is filtered and mixed with a 35.93 MHz oscillator output to produce data about the 44.0 MHz IF frequency. A SAW filter rejects all but the desired data.

Abstract: A single sideband modulator circuit for modulating an optical signal with an RF signal to provide a frequency shift to the optical signal. The modulator circuit utilizes a dual path modulator having an electrical terminal and two optical terminals. An RF signal is provided to the electrical terminal and an optical signal is provided to each optical terminal so that the optical signal input to one terminal travels in the direction of the RF signal to produce an output optical signal having a carrier band and a single sideband, and the optical signal input to the other optical terminal travels in the opposite direction of the RF signal to produce an output having only a carrier band. A coupler adds the resulting optical output signals so that the carrier bands are cancelled, leaving only the sideband.

Abstract: A communication system having a modulation system for transmitting a symbol set via a single side-band modulated carrier and a demodulation system for recovering the in-phase and quadrature signals from the modulated carrier. The modulation circuit receives M symbol values and generates M time domain samples for each of the in-phase and quadrature signals. The in-phase and quadrature signals can then be combined to generate the single side-band modulated carrier. The modulation circuit includes a transform circuit for generating M transformed symbol values by computing the transform of the M symbol values. A polyphase filter bank having 2M FIR filters is used to process the output of the transform circuit. Each filter has g taps, where g is an integer greater than 1. The outputs of the polyphase filters are combined with the outputs of the polyphase filters generated from a previously received set of M symbols to generate the M time-domain signal values of the in-phase signal.

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 vestigial-sideband amplitude-modulation transmitter using a balanced modulator for generating a suppressed carrier that is in quadrature phasing with the video carrier of a television signal receives as modulating signal a binary phase-shift-keying (BPSK) signal encoding digital signals. The quadrature transmission reduces the visibility of the lower-frequency PSK sidebands in the TV signal as viewed on screen. The symbol rate of the PSK is made to be a multiple of the horizontal line scan rate of video signal. To reduce the visibility of the higher-frequency PSK sidebands in the TV signal as viewed on screen, the BPSK is transmitted twice during respective frames of successive pairs of data frames, which data frames recur at the same rate as video frames. To reduce the interference of video with the PSK, the PSK is subjected to partial-response filtering at the transmitter and is highpass line-comb filtered at the digital signal receiver.

Abstract: A Single-Sideband (SSB) modulator includes:a demultiplexer for successively distributing an A/D converted digital signal x(t) to L sequences x.sub.1 (t.sub.1), x.sub.2 (t.sub.2)... ...x.sub.L (t.sub.L) in accordance with a sampling period t, an adder including L/2 adders for adding constants to x.sub.i (t.sub.i) of the demultiplexer, where i is either an even or an odd number; a phase shift network system comprising L/2 phase shift networks for making a 90-degree phase difference between the outputs of the adder and x.sub.i (t.sub.i) of the demultiplexer; a timing signal generator for generating timing signals expressed by A(-1).sup.(KL)/2+n and/or A(-1).sup.((K-1)L)/2+n in accordance with the sampling period t; a multiplier including L/2 pair of multipliers for multiplying the outputs of the phase shift network system by the outputs of the timing signal generator; a multiplexer for selecting the outputs of the multiplier in accordance with the sampling period t.

Abstract: A synchronous detector for demodulating and decoding a digital data signal modulated either according to a vestigial sideband or a quadrature amplitude modulation scheme is based upon the principle of recognizing that a vestigial sideband signal may be regarded and treated as an offset-keyed QAM signal. The detector comprises a tuner for tuning to a center frequency symmetrically displaced within the transmitted digital data signal frequency spectrum and a decoder circuit selectively operating to reconstruct the transmitted digital data stream according to the duration of a transmitted data symbol. A related method of demodulating and decoding a modulated digital data stream comprises analogous steps of tuning to a center carrier frequency and selectively switching between in phase and quadrature arms of the demodulator such that the switch resides in one position or the other for a duration equal to half the duration of a transmitted data symbol.

Abstract: Tone signal (34a) having a reference frequency (f) which is produced by the tone signal generation device (34) at the transmitter part is transmitted, via transmitter device (32), antenna (31), aerial line, antenna (32), to the reception sector (12). Then, the received tone signal (12a) is compared by the frequency correction circuit (A) with the preset reference signal (f), and according to a result of the comparison, a frequency produced by the reception sector (12) is corrected. That is, an error produced between the transmission frequency by the transmitter (32) and the reception frequency by the receiver (12) is apparently canceled. Thereby facsimile data can be transmitted so correctly to the receiver part so that the facsimile communication with use of radio SSB system can be successfully applied, although there may be an error between the transmitter frequency and the receiver frequency.

Abstract: A vestigial-sideband amplitude-modulation transmitter using a balanced modulator for generating a suppressed carrier that is in quadrature phasing with the video carrier of a television signal receives as modulating signal a binary phase-shift-keying (BPSK) signal encoding digital signals. The quadrature transmission reduces the visibility of the lower-frequency PSK sidebands in the TV signal as viewed on screen. The symbol rate of the PSK is made to be a multiple of the horizontal line scan rate of video signal. To reduce the visibility of the higher-frequency PSK sidebands in the TV signal as viewed on screen, the BPSK is transmitted twice during respective frames of successive pairs of data frames, which data frames recur at the same rate as video frames. To reduce the interference of video with the BPSK, the BPSK is comb filtered at the digital signal receiver and after symbol detection is subjected to partial-response filtering for recovering the digital signal originally encoded in the BPSK signal.

Abstract: A digital single sideband modulator (10) includes a relatively complex CMOS NCO (14) that drives a relatively simple ECL frequency translator (30). The frequency translator (30) outputs a digital signal that is converted to analog by a D/A (44) and then filtered in a bandpass filter (46) having a pass band including a frequency of twice the NCO's clock frequency. The NCO (14) generates a modulated intermediate frequency NCO signal having quadrature components. The frequency translator (30) multiplies real and imaginary components of the NCO signal by real and imaginary components of digitized SIN, COS sampling functions (48, 50). The resulting products are added together. The adding operation is performed by a multiplexer (32), whose selection input is driven at twice the carrier frequency, and the multiplying operations are performed by a selective negation circuit (34), that is driven at the carrier frequency.

Abstract: A digital circuit having a first section for converting a low-frequency signal into a sampled single sideband signal, coupled to a second section for separating the sampled SSB signal into its two components, the phase and envelope components.