Abstract: A frequency division network is disclosed in which a sinusoidal signal is converted to a digital format for frequency division and then converted back to the sinusoidal format, the sinusoidal output waveform having low phase noise. In a preferred embodiment the frequency conversion takes place in an m-fold plurality of edge triggered flip-flops, connected to divide by two, and clocked by the sinusoidal waveform. Each flip-flop is subject to jitter causing phase noise, which is minimized when the output of two sets of four flip-flops are averaged, and then filtered to obtain the sinusoidal fundamental. When a crystal filter having a very narrow pass band is employed, the phase noise is further reduced. The frequency division network uses low cost components and the phase noise of the output waveform approaches that of a stable crystal oscillator.

Abstract: The invention relates to a two state phase modulator with minimum amplitude modulation. The modulator assumes two phase states differing by .THETA. where .THETA. is a sub-multiple of 180.degree. which permits a phase variation of 180.degree. for phase coded transmissions when the frequency of the phase modulated carrier wave is multiplied by the reciprocal of the sub-multiple. Three equal components are derived in the phase modulator: an in-phase, an out of phase, and a quadrature phase component. The out of phase component is delayed in relation to the in-phase component by .THETA./2, while the quadrature phase component is delayed .THETA./4. The in-phase and out of phase components are then reduced by a factor (2 sin .THETA./2) selected such that when added to the quadrature component, the resultants have a magnitude equal to that of the quadrature component and differ in phase from the quadrature comonent by .+-..THETA./2.

Abstract: Apparatus and method are disclosed for synchronziing the operation of the frequency sensitive devices of two or more transceiver units in a secure, wireless communication system. A fixed frequency pilot signal is generated in a first unit of the system and transmitted to the other units. The encoding noise signal locally generated in each unit is timed by clock pulses derived from the locally available pilot signal. If synchronism between the respective noise signals is lost, the pilot signal is disabled. This causes a reset pulse to be generated in each unit. The action resets each noise generator and restores synchronous operation.

Abstract: An AM superheterodyne radio receiver has an RF filter which includes a biased varactor for providing a trimming capacitance and provides an AGC signal when it is tuned to a broadcast AM signal. The AGC signal and a derived time derivative signal are used to provide binary signals which drive a logic circuit and the logic circuit controls a generator which biases the varactor. The biased varactor fine tunes the RF filter towards the carrier frequency of the broadcast AM signal.

Abstract: In differential amplifier circuits of the type having first and second transistors, the emitter of each transistor is connected to a different current source and the emitters are coupled by a ceramic filter tuned to 455 KHz. In one embodiment, wherein the transistors have symmetrical resistive loads, an inductor is connected across the filter to tune out capacitance across the terminals of the filter. In another embodiment, the circuit includes an unbalanced and complex load. In yet another embodiment, the circuit has active load circuitry and an inductor is connected across the filter to tune out capacitance across the terminal of the filter.

Abstract: An FM receiver includes a varactor tuned RF filter to which is applied a bias voltage and a 20 Hz sinusoidal signal for varying the varactor capacitance and the resonant frequency of the filter. As a result, an FM broadcast signal in the pass-band of the filter is phase-modulated by the filter. The second harmonic of the phase modulation is recovered and coupled to a synchronous detector driven at a 40 Hz rate to provide an error voltage. The bias voltage is related to the integral of the error voltage. A difference between the frequency about which the tuned circuit periodically varies and the carrier frequency of the FM signal cause the bias voltage to vary so as to reduce the magnitude of the difference, thereby fine-tuning the receiver.