Antenna noise reduction apparatus and method, especially suitable for airborne service, including an antenna discharging circuit for periodically grounding the receiver antenna through a switching system at a frequency substantially higher than the carrier frequency of the radio system with which the receiver operates.

A method of sampling transmissions in telecommunication systems including the steps of rectification and logarithmic amplification of the voltage present at a point in the system and application of such rectified and logarithmically amplified voltage to a linear voltage indicating device is disclosed. Apparatus for practicing the method and particular circuitry for use in such apparatus is described, which circuitry includes a half wave voltage rectifier circuit including a direct current feedba...

In a time division multiple-access communications system using a satellite transponder and a plurality of earth stations, each earth station periodically transmits bursts of data which are timed so that the bursts from the earth stations in the system interleave and do not overlap in time when received at the satellite. The total time for transmitting one burst from all stations is the frame time of the system. Each burst is subdivided into numerous time slots or channels during which digital in...

A superconductive resonant cavity is energized with radio-frequency energy. The cavity includes a tuning stub having a piece of semiconductor material mounted on the end thereof. An incoming communication signal modulates a light source optically coupled to the semiconductor by a fiber optic bundle. This varies the dielectric constant of the semiconductor which, in turn, varies the resonant frequency of the cavity. An angle modulation demodulator senses the frequency of the radio-frequency oscil...

An automatic noise nulling circuit for use with a signal transmission system with noise sensed and nulled from the signal path. Noise is nulled out by a null signal input with substantially no distortion of desired signal transmission and without altering the signal transmission characteristics of the signal path through the system.

A method and apparatus for reducing crosstalk in microwave transmission systems in which information is transmitted in two cross-polarizations or channels. Utilizing a frequency-diversity system, a pilot signal is transmitted with each of the channels; and the receivers are equipped with means for detecting components of the pilots received in each channel to indicate the level of crosstalk. The components of the pilots are processed at the receiver in a predetermined manner to generate control ...

An antenna system, used for simultaneous reception and transmission, is coupled by way of a hybrid device to an RF amplifier having less gain than the isolation loss introduced between its output and input by the hybrid. Additional gain, beyond the finite isolation of the hybrid, is provided by an oscillator which is coupled in single-port fashion to the circuit and tends to synchronize with applied signals that are substantially weaker than its output.

A system for cancelling or suppressing the amplitude of the carrier and sideband signals of a radio transmitter to facilitate analysis of spurious and noise outputs from the transmitter is disclosed. The system includes means for deriving a carrier cancelling signal from an actual sample of the transmitter output, signal processing circuitry and summing means. Also, an electromechanical signal controller is disclosed capable of continuously correcting the amplitude of the cancellation signal by ...

Underdamped audio phase shift oscillator connected across the audio voltage amplifier section of a radio receiver that sharply increases the selectivity or the response to signal of predetermined frequency and simultaneously relatively attenuates all other frequencies transmitted to output of receiver. The feedback circuit included in the phase shift oscillator is particularly useful in improving the selectivity of a radio receiver working in the continuous wave (C.W.) mode.

The channel impulse response of a communication channel is determined from measurement of the cross correlation between the channel output signal and a delayed locally generated pseudorandom noise sequence signal. The undelayed pseudorandom noise sequence signal is utilized as a probe signal and is added to any information signal prior to being supplied to the communication channel being monitored. The output of the channel is hard limited and polarity-coincidence compared to the time-delayed ps...