Abstract: A three level signal is converted to a two level signal for transmission through a bi-level digital device by separating the opposite polarity parts of the three level signal. One part is inverted at an inverter and devices such as monostables are used to form two pulse trains in which the pulse lengths are different. The pulse trains are combined at a mixer and then transmitted through the device. Also disclosed is a decoder for decoding the pulses after transmission through the device.

Abstract: An FM diversity receiver system and method are disclosed which include two antennas and a switch for switching the receiver from one antenna to the other. A fade control signal is produced which is related to the received FM signal, in which fade control signal both multipath and non-multipath disturbances are manifested. Disturbances in the fade control signal are compared with a threshold voltage and, when the disturbance exceeds the threshold voltage, antenna switching is momentarily prevented to prevent antenna switching in response to electrical noise impulses, such as ignition noise, which are shorter than the period during which antenna switching is momentarily prevented. If the fade control signal disturbance continues to exceed the threshold voltage after the momentary period of disablement, the threshold voltage is reset to a level related to the maximum level of the fade control signal disturbance, after which antenna switching takes place.

Abstract: The invention relates to a high frequency mixer stage comprising a field-effect transistor tetrode having two gate electrodes, with one gate electrode being supplied with the high frequency input signal. According to the invention, the mixer stage becomes a frequency changer by means of inductive load at the second gate electrode of the tetrode.

Abstract: In an apparatus for receiving a burst signal intensity-modulated by a signal obtained by Manchester-code converting each code of an input signal into a pair of codes, the received burst signal is converted by a partial response circuit into an AC signal and then AC-amplified. From the received burst signal is extracted a timing signal of the same frequency as the clock frequency of the Manchester-coded signal. In a decision circuit, the AC-amplified output is decided by the timing signal, through using a decision level close to zero, at the timing of each of former and latter codes of the Manchester-coded pair codes. A coding rule violation is detected in a plurality of successive decision output codes to detect a reception abnormality such as asynchronism and a signal collision. The decision output is decided at the timing of the latter one of the Manchester-coded pair codes, thereby regenerating transmitted information.

Abstract: A method of predistortion alignment of a single sideband transmission system in which the receiver becomes a part of the signal path which is predistorted, to providing improved overall intermodulation distortion. A convenient method of performing the alignment under field conditions is disclosed.

Abstract: In radio communication system using angular modulation, the presence and quantity of cochannel interference is detected. According to the invention, when desired signal and undesired signal are received simultaneously, an envelope of the received IF output signal involves low frequency spectrum component similar to that of fading and high frequency spectrum component with several KHz. The low frequency spectrum component and high frequency spectrum component are then calculated, and the interference ratio D/U is obtained by processing said components.

Abstract: In a radio system wherein a read signal generator generates a read signal constituted by a plurality of bits, the read signal is supplied to a memory circuit for storage of data to read out the data, and the read out data determines the frequency generated by a synthesizer, the memory circuit and a holding circuit are packaged on an independent substrate, and the read signal generator comprises a first read signal generator generating about half the bits which is held in the holding circuit and a second read signal generator generating the remaining bits.

Abstract: A system for the automatic establishment of a shortwave telegraphy signal connection between two transmitter-receiver stations within a frequency range subdivided into several channels. Both stations use their receiver to determine objective measurement values reflecting the transmission conditions over the individual channels. Active and passive channel analysis of the actual quality of the signal transmission is determined at each channel. The transmitter of the calling station is automatically tuned to the channel which corresponds to the best channel quality stored in its memory. A predetermined time after transmitting the call signal, the calling station switches to reception and upon reception of an acknowledgment signal from the counter station automatically begins the message transmitting-and-receiving operation. If after a predetermined time no acknowledgment signal is received, the transmitter automatically switches to the channel stored in its memory with the next best channel quality value.

Abstract: A transmitted signal includes a pilot signal at a given frequency and an information signal occupying a different band of frequencies. A noise reduction system for a signal receiver detects modulation on the pilot signal and generates a signal having a frequency that varies in response to the detected modulation. The system includes an apparatus for combining the received signal with the generated signal to produce a signal at another frequency with reduced frequency noise.

Abstract: In a double superheterodyne tuner, the first local oscillator frequency is set to a value higher than the first intermediate frequency, which is set to a value between three and five times the upper limit of the receiving frequency range. With this arrangement spurious signals of at least third or less order can be prevented from occuring in the first intermediate frequency range. The tuner comprises an input filter which attenuates interference signals whose harmonics equal a desired frequency. The second intermediate frequency may be selected such that it is obtained by subtracting the second local oscillator frequency from the first intermediate frequency which is higher than the second local oscillator frequency. As a bandpass filter for passing the first intermediate frequency may be used a coaxial dielectric filter so as to reduce interferences by undesired channel signals.

Abstract: An improved multifrequency trunked, two-way communications system is provided in which a plurality of conventional single channel radio units are provided access. The system includes a predetermined number of information channels that are shared by a plurality of trunked stations. A trunked controller assigns one of the information channels to a requesting trunked mobile unit. The requesting trunked mobile unit is enabled to operate on the assigned channel in response thereto.The improved communications system includes a radio access link which enables the single channel radio units to operate on an assigned information channel in the same manner as the trunked remote stations. The radio access link provides the plurality of conventional remote stations automatic access to the trunked system without requiring any modification of the conventional remote stations, and likewise without modification of the trunked remote stations and trunked controller.

Abstract: An R.F. circuit with at least one R.F. transmission line including a strip conductor (15) and a ground plane (13) on an insulating substrate (3) and having two diodes (24, 25) respectively D.C.-connected to two portions (38,39) of the ground plane (13). The two portions are mutually D.C.-isolated by a slot (37) to enable the diodes (24, 25) to be biased. The substrate (3) is mounted in a housing (1, 2) of conductive material, and the two portions (38, 39) of the ground plane (13) are mutually R.F.-coupled via the conductive material. One of the portions (39) is electrically-connected to an adjacent housing member (2) and the other portion (38) is separated therefrom by a thin insulating layer. The slot (37) inhibits coupling of R.F. energy out of the circuit into the slot (37), suitably being very narrow, e.g. 20 .mu.m, so as to form a further transmission line with a very low characteristic impedance and also to have a high attenuation along its length for operation at mm-wavelengths.

Abstract: Apparatus for processing speech in radioelectric transmitter/receiver equipment is adapted to transmitting and receiving speech. The apparatus comprises a compression circuit for compressing the dynamic range of the speech signal, said compression circuit being formed by at least one variable transmission attenuator for maintaining the level of speech modulation substantially constant throughout speech transmission. An expander re-establishes on reception the level of speech before it was compressed. An expander control device is responsive to the attenuation value applied by the transmission attenuator and transmitted over an auxiliary radioelectric frequency channel of the equipment. The compression circuit is an incremental compression circuit with a time anticipated action.

Abstract: Systems for preventing channel blockage on aircraft voice communication frequencies caused either by a pilot beginning a transmission while someone else is transmitting on the same channel (i.e., "stepping on" or "blocking" the first transmission), or by a "stuck microphone" condition resulting from undesired activation of the microphone switch circuit. In accordance with the invention, a "step-off" device (SOD) and a "stuck microphone reliever" (SMR) are combined in a single device, termed an "anti-blocking device" (ABD). The entire device may be provided in retrofit form and draws all its operating power from the radio push-to-talk switch line, with no internal modification to the radio required. The step-off device portion of the anti-blocking device senses when a selected radio frequency is in use, and when in use, prevents transmission even when the microphone switch circuit is operated.

Abstract: A simplex radio transmitting and receiving apparatus, has a transmission blocking means which prevents selection of the transmitting mode of the apparatus if a signal of predetermined strength is being received by the apparatus at the time the press-to-talk key is operated. An over-ride circuit enables the blocking means to be disabled in an emergency or if another transmitter has been left operating in error. The over-ride circuit can be activated by, for example, repeated operation of the press-to-talk key, and ceases to operate when the key is released to return the apparatus to its receiving mode. Also disclosed is a transmission control means which can be used to modify existing transceivers to operate in accordance with the invention. In a further feature of the invention, means are provided to detect the higher power consumption of the transceiver in the transmit mode and thereby to give a warning of an unduly extended transmission, e.g. by faulty equipment.

Abstract: An improved method and apparatus for measuring the strength of a radio frequency (RF) signal subject to Rayleigh fading is described. The strength of the RF signal is sampled two or more times during a predetermined time interval and the sampled signal strength having the largest magnitude is selected. The selected signal strength is a reasonably accurate measure of the signal strength since the true average strength of a Rayleigh fading signal is close to its peak signal strength. The inventive method and apparatus is particularly well adapted for use in a scanning receiver located in a base station radio of a cellular radiotelephone communications system.

Abstract: The invention relates to switches enabling the connection by an optical method of at least one of the circuits of a set of input circuits to at least one circuit of a set of output circuits. It consists in illuminating a photosensitive medium with parallel input beams coming from a set of input circuits. The input beams are then diffracted on strata inscribed on the medium to reach one of the circuits of a set of photoreceptor circuits. The strata are inscribed by interference of two inscribing beams of which the wavelength differs from that of the input beams; the wavelength of these input beams not lying within the range of spectral sensitivity of the photosensitive medium.

Abstract: An R.F. balanced mixer comprises on an insulating substrate (3) with opposed major surfaces a balanced first transmission line having a pair of conductors (18, 19) on a first major surface and an unbalanced second transmission line having a strip conductor (15) on one major surface and a ground conductor (13) on the side of the substrate (3) remote from the strip conductor (15). Two diodes (24, 25) are electrically connected between the pair of conductors (18, 19) of the first line and the strip conductor (15) of the second line to form an arrangement operable as a 180.degree. hybrid junction, the first line coupling an R.F. signal to the diodes (24, 25) and the second line coupling an L.O. signal to and an I.F. signal from the diodes (24, 25). To reduce the impedance of the I.F.

Abstract: The interpolation device for the voice coded in DELTA transmission and transmitted on a fixed frequency or with frequency jumps carrier, comprises in parallel on a classic reception network, a jamming detection device being able to be constituted by a high-pass filter in order to detect the components outside the modulated signal band, a detector circuit with threshold fixing the level of the outside band components characterizing a jamming and possibly a monostable circuit. It comprises, furthermore, a rumbling generator that transmits to the input of the DELTA decoder a rumbling sequence in place of the sequence detected on a stage when this sequence is reckoned as jammed by means of a switch controlled by the output of the monostable circuit.

Abstract: A receiver including an FET frequency mixer is disclosed. A local oscillator generates a local oscillator signal which is applied to a first amplifier whose gain is varied as a function of a control signal applied thereto. The output of the first amplifier is applied to a first gate electrode of the FET frequency mixer. A high-frequency signal received by the receiver is applied to a second amplifier whose gain is also controlled by the control signal. The output of the second amplifier is applied to a second gate electrode of the FET frequency mixer. The control signal is generated as a function of the output of the FET mixer.