A spread-spectrum signal comprises a spreading waveform modulating a carrier wave and containing a real linear combination of a first waveform at a first waveform rate and a second waveform at a second waveform rate, the first waveform rate being distinct from the second waveform rate and both waveform rates being distinct and non-zero. The linear combination of the first and the second waveform is modulated with at least one binary sequence comprising a signal identification code.

In a short wave transmission method, a carrier in a short wave band is circularly polarized and radiated from an antenna, thereby removing an influence of fading. A short wave transmission apparatus has a transmission apparatus including a carrier generation unit, a subcarrier generation unit, a first mixer, a phasa shifter, a second mixer, and two orthogonal dipole antennas. The carrier generation unit generates a carrier in a short wave band. The subcarrier generation unit generates a subcarrier. The first mixer receives the carrier and the subcarrier. The phase shifter phase-shifts the subcarrier generated from the subcarrier generation unit by π/2. The second mixer receives the carrier and a subcarrier which is phase-shifted by π/2 by the phase shifter.

A method of processing certain offset-carrier modulated ranging signals which are synchronously broadcast with another signal having a nearby centre frequency. The method comprises receiving a first radionavigation signal from at least one of a plurality of transmitters and deriving therefrom a first OCM signal S_A, and generating a combined correlation value Y_C, the combined correlation value Y_C corresponding to the correlation of a combined signal S_C with a replica of the first OCM signal, the combined signal S_C resulting from the coherent combination of first OCM signal S_A with a second signal S_B having the same or nearby centre frequency to the first OCM signal S_A. The method further comprises deriving ranging information based on the combined correlation value Y_C. The second signal S_B may comprise one of (i) an OCM signal and (ii) a BOC signal. The combination of the two signal components may be done before or after the correlation operation. When adopted by a ranging receiver, the technique offers improved performance in the area of: signal acquisition and reacquisition, in particular reducing the likelihood of side-peak acquisition; fine-acquisition and tracking: reducing or eliminating the likelihood of false code-lock.

In a single-chip multistandard video modulator arrangement in which audio signals for transmission with video signals are first modulated onto a subcarrier and then combined with the video signals for modulation onto a VHF or UHF main carrier, the modulated subcarrier signals are passed through a high-pass filter before being combined with the video signals in order to reduce the amplitude of any audio frequency components, and the resulting variations in main carrier amplitude, which tend to produce "sound on vision" effects.

An optical communication system (Figs. 1-4, 6-7) which includes an optical transmitter (Fig. 1) for transmitting an optical signal through a single-mode optical fiber (22, 88) to an optical receiver (Figs. 3, 9, 10). The optical transmitter includes an optical source for generating a light beam. The optical source is preferably a high speed laser diode (20, 86) emitting in a spectral range of 1.3 - 1.6 micrometers. The light beam is intensity modulated with a composite modulation signal comprising one or more modulated microwave subcarriers and a baseband digital signal. The microwave subcarriers are typically in the frequency range between 2 and 20 gigahertz, and the baseband digital signal is typically a time-multiplexed signal carrying multiple voice and data channels. By simultaneously transmitting a baseband digital signal and multiple microwave subcarriers on a single optical fiber, the information-carrying capacity of the optical communication system is increased.

In a short wave transmission method, a carrier in a short wave band is circularly polarized and radiated from an antenna, thereby removing an influence of fading. A short wave transmission apparatus has a transmission apparatus including a carrier generation unit, a subcarrier generation unit, a first mixer, a phasa shifter, a second mixer, and two orthogonal dipole antennas. The carrier generation unit generates a carrier in a short wave band. The subcarrier generation unit generates a subcarrier. The first mixer receives the carrier and the subcarrier. The phase shifter phase-shifts the subcarrier generated from the subcarrier generation unit by π/2. The second mixer receives the carrier and a subcarrier which is phase-shifted by π/2 by the phase shifter.

In a single-chip multistandard video modulator arrangement in which audio signals for transmission with video signals are first modulated onto a subcarrier and then combined with the video signals for modulation onto a VHF or UHF main carrier, the modulated subcarrier signals are passed through a high-pass filter before being combined with the video signals in order to reduce the amplitude of any audio frequency components, and the resulting variations in main carrier amplitude, which tend to produce "sound on vision" effects.

An optical communication system (Figs. 1-4, 6-7) which includes an optical transmitter (Fig. 1) for transmitting an optical signal through a single-mode optical fiber (22, 88) to an optical receiver (Figs. 3, 9, 10). The optical transmitter includes an optical source for generating a light beam. The optical source is preferably a high speed laser diode (20, 86) emitting in a spectral range of 1.3 - 1.6 micrometers. The light beam is intensity modulated with a composite modulation signal comprising one or more modulated microwave subcarriers and a baseband digital signal. The microwave subcarriers are typically in the frequency range between 2 and 20 gigahertz, and the baseband digital signal is typically a time-multiplexed signal carrying multiple voice and data channels. By simultaneously transmitting a baseband digital signal and multiple microwave subcarriers on a single optical fiber, the information-carrying capacity of the optical communication system is increased.