Abstract: A radio frequency transmission system contains at least one coherently modulated information signal, for example, a T.V. signal. At a transmission, the information signal is combined with two pilot tones, F1 and F2, related by the equation F1=N/M F2, where N and M are integers. The combined signal is suppressed-carrier modulated at microwave frequencies and transmitted to a receiver. At the receiver, the signals are demodulated by a local oscillator. The two pilot tones are then separated from the information signal and are compared to each other. The local oscillator frequency is controlled in response to this comparison such that the pilot tones at the receiver bear the same relationship to each other that they had at the transmitter. When this is achieved, the local oscillator frequency is the same as the suppressed-carrier frequency and co-channel interference is prevented.

Abstract: A processing circuit for efficiently amplifying radio frequency signals while generating minimal splatter includes a first channel having an envelope detector for generating a rectified envelope signal from a modulated radio frequency input signal provided thereto. The first channel includes a peak clipping circuit which clips portions of the rectified envelope signal having an instantaneous voltage less than a first selected threshold level. A second channel includes a symmetric clipping circuit for symmetrically clipping portions of the modulated radio frequency input signal which exceed a second voltage threshold level.

Abstract: A diode mixer arrangement including a mixer stage connected for receiving a signal having a frequency to be converted and an oscillator signal having one of a plurality of preselectable oscillator frequencies. The mixer stage includes diodes arranged to be biased by a predetermined direct control voltage for the compensation of parasitic influences. A voltage branch is connected to the mixer stage for producing the predetermined direct control voltage. The voltage branch includes a memory device for storing a plurality of data signals each of which represents a predetermined direct control voltage corresponding to a respective one of the plurality of preselectable oscillator frequencies. The memory device has an input for receiving an input signal which represents the preselectable oscillator frequency of the oscillator signal received by the mixer stage and an output for reading out the corresponding data signal which is used by the voltage branch to generate the predetermined direct control voltage.

Abstract: A transmitter for single-sideband broadcast transmission which operates in accordance with the principle of combined amplitude and phase modulation generating a single-sideband signal and splitting this signal into an amplitude-modulated component applied to an amplitude-modulated path and a phase-modulated component applied to a phase-modulated path. An amplitude-modulation path is a D.C. voltage-coupled signal path from an envelope-curve detector to a radio-frequency amplifier (2). This results in direct floating-carrier modulation in a radio frequency amplifier in which the amplitude-modulated and phase-modulated components are amplified and recombined.

Abstract: A trigonometric transform function generator provides a signal which is either the sine or cosine function of an inputted information signal. The function generator can be used in an FM system or in a new system of transform modulation, wherein the transform functions are used to derive the original information signal.

Abstract: A compressed single side band communication system and method in which the audio signal is compressed prior to pre-emphasis and thereafter summed with a pilot tone for further compression prior to transmission. Initally, only the pilot tone is transmitted at full rated power to aid in acquisition of the signal by the receiver. Thereafter, the transmitter ALC is disabled and the pilot tone is attenuated. The receiver adjusts the frequency characteristics of the pilot tone filter and phase lock loop filter in the detector as a function of lock-on. The delay after loss of lock-on in reverting to wide band pilot tone and wideband loop filters is varied as a function of signal strength. The pilot tone may be modulated for tone coded squelch. The modulating source is located in the return end of the phase lock loop filter. A unique filter is provided to insure acquisition of the pilot tone.

Abstract: A single carrier is amplitude-modulated by a signal which is a transform (as the sine function) of the audio signal, and one set of sidebands is removed. In a receiver, the signal can be recovered by first deriving the Hilbert transform of the sine transform, and multiplying it by the signum of the derivative of the original audio signal to obtain the cosine transform. The sine and cosine transforms are then decoded to obtain the original audio signal.

Abstract: The modulating device reduces the number of electronic functions required for generating an SSB signal which is subjected to SSB peak-limiting in a transmitter which is selectively operable either on the upper channel or on the lower channel. By means of a mixer, the signal delivered by the peak-limiter is mixed with a signal whose frequency is double that of the local oscillator. By filtering the signal thus obtained by means of the filter which is symmetrical with the filter employed for carrying out SSB modulation, the signal to be transmitted on one of the channels is thus obtained. The signal to be transmitted on the other channel is obtained by reversing the position of the two filters.

Abstract: A balanced modulator, producing a double sideband suppressed carrier (DSBSC) output achieves carrier suppression and linear performance suitable to modulate frequency division multiplexed signals with stringent interchannel interference requirements. It is simply and inexpensively realized through the use of two logic gates which are arranged in a dual complementary fashion, so that their output terminals go high and low alternately, and which drive a center-tapped transformer through coupling capacitors to provide the required switching function necessary to produce the DSBSC output. The modulator circuit has the added feature that the square wave carrier source that is applied to the logic gates can be the means of activating the circuit, thereby eliminating the need for a separate power supply.

Abstract: A microwave transmitter comprises a signal modulator for receiving an input signal that includes up to 75 video and audio channels and producing an amplitude modulated signal in the microwave frequency range corresponding thereto. An amplifier responsive to the microwave frequency signal produces an amplified output signal suitable for transmission to a remote location. The signal modulator and the amplifier have upper power limits which are sufficiently below their respective two-tone third order intermodulation intercept points that the carrier-to-triple-beat power ratios of each are respectively at least equal to first predetermined values. The gain of the amplifier is high enough that, notwithstanding the power limitation imposed on the microwave frequency signal by virtue of the upper power limit of the signal modulating means, the power of the amplified output signal is at least equal to a second predetermined value.

Abstract: A television transmitter comprises a video processing circuit (2) an amplitude modulator (4) a vestigial sideband filter (8) an R.F. amplifying stage (9) and a klystron amplifier (10) which feeds an antenna (22). The klystron is provided with a grid electrode (12) to which a video signal is applied to modulate the density of the electron beam. The video signal applied to the grid electrode (12) is derived from the output of the video processing circuit (2) and fed via a low-pass filter (6) and a d.c. isolating circuit (20) to an amplifier (21) which provides a signal of the desired amplitude at the grid electrode (12). The filter (6) is arranged to restrict the bandwidth of the video signal applied to the grid electrode (12) to less than that of the vestigial sideband in order to reduce the possibility of re-inserting the higher frequencies into the vestigial sideband. The d.c.

Abstract: Suppressing the L.O. leakage signal in the second converter section of a gle sideband generator by utilization of a generator bypass circuit which supplies a signal at the generator output which in turn cancels the leakage L.O. signal.

Abstract: Single sideband modulation system. A first single sideband of radio frequency is generated with first audio modulation on the lower side of an assigned frequency, the first single sideband bandwidth being equal to the highest frequency of said first audio modulation. A second single sideband of radio frequency is generated with second audio modulation on the upper side of the assigned frequency, the second single sideband bandwidth being equal to the highest frequency of said second audio modulation. A first stereo channel is modulated on the lower sideband frequency. A second stereo channel is modulated on the upper sideband frequency. The stereo channels are combined whereby a receiver tuned to the assigned non-transmitted carrier frequency will receive both stereo channels.

Abstract: A system for single sideband modulation, and a method implemented by the system. The system includes a double sideband, suppressed carrier modulator and a phase locked loop circuit receiving the output of the modulator and tuned to lock to one of the sidebands of the modulator output. The phase locked loop circuit produces an output having a constant amplitude, but otherwise tracking the signal contained in the one sideband. The output of the phase locked loop is processed by an amplifier having a controllable gain. Open and closed loop circuits are provided for deriving the amplitude of the signal contained in the one sideband. The latter amplitude is imparted to the output of the phase locked loop by using the signal amplitude to control the gain of the amplifier.

Abstract: A method and apparatus for suppressing carrier leakage components in a system for modulating a carrier with a selected signal wherein the carrier and a quadrature component of the carrier are weighted and summed with the modulated carrier to produce a component substantially equal and opposite in phase to the leakage component so that the summing substantially cancels or suppresses the leakage component.

Abstract: For measuring the group delay of amplitude modulated transmitters a variable measurement frequency is modulated by a fixed frequency so as to obtain the sum and difference frequencies which are sent to the input of the transmitter under test; the two waves corresponding to the same side-band are obtained at the transmitter output, are frequency shifted, filtered and detected to give their beat, filtered again to obtain only the beat at a frequency twice the modulation frequency; and said beat is compared with a signal of the frequency but coherent with the modulating signal, the comparison providing a direct voltage component which is a linear function of the group delay of the side-band corresponding to the measurement frequency. The invention also concerns the apparatus for realizing the method, comprising also the known units allowing to measure the amplitude of each side band.

Abstract: Disclosed hearing aids have circuits that produce a suppressed-carrier modulated signal and they include an electrode to be applied to the head of the user for coupling the suppressed-carrier modulated signal to the user's auditory cortex.

Abstract: Calibration technique comprises the production of a calibration signal hag a single sideband of modulation which is locked to an incoming carrier. The sideband may be on either side of the carrier and is phase adjusted to be amplitude modulated, frequency modulated or a combination of the two modulation forms.

Abstract: A suppressed carrier radio signaling system is described in which there is a servo loop utilizing balanced circuit techniques and using the carrier as the reference, in which a phase detector (or coherent demodulator) constantly senses the phase difference between the carrier source and the carrier component in the output signal to derive an error signal which is used to vary the amount of the carrier component toward zero.