Abstract: The bandwidth of frequency modulated signals is limited in a digital data transmission system by shaping the square digital waveform to form a trapezoidal shaped waveform having a positively-sloped ramp on the leading edge of the waveform and negatively-sloped ramp on the following edge of the waveform. Provisions are made to selectively determine the slope of the ramps and the amplitude of the waveform so that the system can be used with a wide range of data transmission speeds without resort to bandpass filter or component changes as were required in the prior art. Provision is also made for transmission of analog data in the same system by providing a feedback loop which causes the ramping to follow, and thus approximate, the analog waveform. The shaped data signal is fed to a frequency synthesizer which produces a frequency modulated sine wave whose frequency deviation is related to the magnitude of the digital or analog data signal.

Abstract: An arrangement for generating an analog angle-modulated carrier signal of a substantially constant amplitude in response to data signals having a symbol rate 1/T comprises a read-only memory for storing modulation parameters, an addressing circuit responsive to a predetermined number of consecutive data symbols for producing read addresses with a rate q/T, where q is an integer greater than 1, and a signal processor for processing read values to form the analog angle-modulated signal.

Abstract: An MSK modulator includes a source of digital sawtooth signals having a recurrence rate equal to the desired recurrence rate of the unmodulated carrier. The digital sawtooth signal is applied to an adder together with a phase control digital signal. The phase control digital signal phase-shifts the digital sawtooth signal. The phase-shifted digital sawtooth signal is applied to a sine ROM to produce a digital sinusoid with an unmodulated recurrence rate equal to the recurrent rate of the digital sawtooth signal. When the phase control signal is an accumulated signal, the digital sinusoid is frequency-modulated. The phase control signal for MSK modulation is a ramp signal generated by a controlled accumulator. The accumulator includes a controllable clocked adder/subtractor, the output of which is coupled by way of a register back to an input. The other input of the adder/subtractor is coupled to receive a fixed ramp rate controlling word.

Abstract: A phase-locked loop modulation circuit, such as may be used for a data communications purposes, in which undesired level variations are eliminated by employing d.c. coupling entirely. The circuit includes a level converter circuit which converts a logic signal into a signal having substantially equal levels above and below a predetermined voltage, a voltage-controlled oscillator, and a circuit for superposing the signal having substantially equal levels on a control voltage of the voltage-controlled oscillator so that the output of the voltage-controlled oscillator is subjected to angular modulation.

Abstract: A frequency modulator comprises an oscillator circuit, and a phase adder circuit receiving a signal derived by phase-shifting an oscillation output of the oscillator circuit by 90.degree. and multiplying the phase-shifted signal by a modulating signal, and adding the product, thereby varying an oscillation frequency of the oscillator circuit. The frequency modulator is characterized in that the amplification elements of the phase adder circuit and the oscillator circuit are connected in parallel with respect to a power source.

Abstract: The present invention is a method and a device for the frequency modulation and/or demodulation of a signal applied to materials that carry sliding charge density waves. A particular example of such a material is orthorhombic TaS.sub.3 that acts as a frequency modulator.

Abstract: In FM transmitters, particularly land mobile FM transmitters, wherein a speech signal is pre-emphasized between 300 Hz and 3 kHz, whereafter it is filtered to provide a sharp cut-off and wherein the maximum peak frequency deviation is limited in order to maintain channel integrity, the level of undistorted speech can be raised to within 90% of the transmitter peak deviation by directly connecting an amplitude limiter to a filter amplifier which behaves as a level sensitive filter when the speech signal has been limited and prevents ringing and overshoot from occurring. The output from the filter amplifier is coupled to a low pass filter, typically a fourth-order Butterworth filter, via an attenuator which reduces the amplitude of the signal to prevent the onset of further clipping.

Abstract: A 16-quadrature amplitude modulation (QAM) modulator for radio links converts a train of data into signals having a phase selected from sixteen predetermined phase values and an amplitude selected from four values. The modulator divides the data train into two data sub-trains. The two data sub-trains are respectively applied to a pair of four-phase modulators that are fed by a carrier source. The 16-QAM modulator also comprises two phase locked loops each including a voltage controlled microwave oscillator and an associated differential phase detector. The differential phase detector responds to the output of the associated four-phase modulator and the output of the associated voltage controlled microwave oscillator. Predetermined parts of the output signals of the two phase locked loops are added.

Abstract: A phase modulation method and apparatus for modulating the phase of a carrier wave in accordance with a binary modulating signal to produce a modulated wave. At least one of the amplitude and the phase of the carrier wave or the modulated wave is corrected by predetermined amounts in response to the value of the binary modulating signal, so that the phase position of the modulated waves becomes equal to one of a number of predetermined positions and so that the amplitudes of the modulated waves coincide.

Abstract: A single sideband communications system conveying a message through a transmitter to one or more predetermined receivers which are enabled by a coded squelch signal unique to the predetermined receivers is disclosed. The transmitter comprises means to angle modulate both the pilot signal and the information bearing single sideband signal with the coded signal at a predetermined deviation and to transmit the resulting signal.Each receiver frequency control means tracks the frequency excursions of a selected portion of the transmitted signal up to predetermined limits so that the message can be demodulated without frequency distortion being introduced. Each receiver demodulates the coded squelch without interfering with the message demodulation or tracking functions and activates the receiver squelch of those preselected receivers.

Abstract: A frequency modulator comprises an oscillator circuit, a phase shift circuit for phase-shifting an oscillation output of said oscillator circuit by 90 degrees, a multiplier circuit for multiplying an output of the phase shift circuit by a modulating signal, and a phase adder circuit for varying an oscillation frequency of the oscillator circuit by adding the output of the multiplier circuit. The amplification elements of the phase adder circuit and the oscillator circuit are connected in parallel with respect to a power source. The multiplier circuit comprises an amplification element connected to receive the output of the phase shift circuit. A constant current source circuit is connected in series with the amplification element of the multiplier circuit and serves to vary the magnitude of current passing therethrough in accordance with the modulating signal.

Abstract: Improved radio transmitter modulation control circuitry is described which significantly increases the average power of the modulating signal, resulting in enhanced audio signal quality since the signal-to-noise ratio is likewise increased. The inventive modulation control circuitry includes a microphone 110, audio amplifier 120, splatter filter 130, modulator 150, potentiometer 140, oscillator and transmitter 180, and antenna 190. The audio amplifier 120 further includes an operational amplifier 160 having an input resistor 162 coupled via capacitor 168 to microphone 110, a phase-lag filter 170 coupled to the output of the operational amplifier 160, and a feedback resistor 161 coupled between the filter 170 and the input resistor 162. When driven into amplitude limiting, the phase and amplitude of harmonic signals from the operational amplifier 160 are altered by phase-lag filter 170 to produce a waveform similar to that shown in FIG. 2.

Abstract: A system including a frequency ramp generator feeding a transmitting power amplifier and antenna through a phase modulator and gain-controllable, transmitter driver stage. The frequency ramp generated is sampled out through a wide band delay-line feeding a phase comparator, the other comparison input to the phase comparator being provided by a sampling probe at the transmitting power amplifier output. The phase comparator output is used as a phase correction signal applied to the phase modulator and an amplitude modulation detector also responsive to the signal on the transmitting power amplifier output provides a feedback signal controlling the gain of the transmitter driver on a high bandwidth basis. Accordingly, instantaneous and long term frequency ramp phase and amplitude variations are substantially cancelled out so that the power amplified output is an accurate replica of the originally generated frequency ramp.

Abstract: An FM transmitter is disclosed wherein a solid state microwave source at a first frequency is frequency modulated with a baseband signal, and a second such source at a different frequency is frequency modulated with the baseband signal inverted. Each of the modulated carriers is frequency doubled and input to a mixer. The output of the mixer is a carrier, having a frequency which is twice the difference of the two microwave frequencies, and frequency modulated by the baseband signal. An automatic frequency control circuit inputs equal and opposite control voltages to the two microwave sources.

Abstract: A first stream of digits is converted to a second stream of alternating-current digits, each of the same amplitude and the same duration which may be different from the duration of the digits of the first stream, and which transmits at least the information in the first stream of digits at at least the same information rate. A number of alternating-current sources with different frequencies, the number at least as great as the greatest possible number of materially different groups of digits in the first stream, are connected one at a time to an output circuit in response to the first stream of digits to generate the second stream of alternating-current digits. The resultant wave may be limited at non-regenerative repeaters to remove amplitude noise, and may be regenerated in regenerative repeaters to remove substantially all noise and distortion.

Abstract: An audio waveform is modified before being applied to a typical FM stereo generator having a low-pass filter which normally produces ringing in response to a clipped signal by pre-emphasizing the audio and reducing the level of that pre-emphasized audio when reaching the maximum allowable modulating signal level. This pre-emphasized audio level is reduced by an amount determined by the ringing in the low-pass filter in the stereo generator to follow.

Abstract: An audio processor for an FM stereo system including a peak clipping circuit to prevent overmodulation further includes means responsive to the audio signal before and after the clipping means for detecting the amount of energy lost due to peak clipping and gain control means for reducing the amplitude level of the clipped audio signal in proportion to the peak energy lost to prevent overmodulation due to the shifting of the entire signal level which is associated with any asymmetry of the clipped signal.