Abstract: An AM stereo transmitter with bandwidth limiting utilizes the detection of high frequency energy in the modulating signal to control the difference channel input to the stereo encoder.

Abstract: A re-regulation circuit operates in the environment of a vehicle alternator/charging system and cooperates with the standard regulator to prevent momentary loss of load from reducing the field excitation to such an extent that the alternator AC output is too low for proper functioning of such AC-dependent circuits as the tachometer circuit. Re-regulation is prohibited in the event of a true fault in the system. The temporary condition is not indicated to the user as a true fault.

Abstract: A door operator system includes up and down limit switches actuated to the closed position when the door reaches the up and down travel limits. A processor circuit within the operator is connected to the limit switches for ascertaining the position of the door. Bias circuits apply a bias to the processor when the limit switches are open. An indicator system comprising a pair of light emitting diodes connected across respective limit switches indicates the door position. A series impedance element common to both LED circuits prevents actuation of the control circuit by the light emitting devices.

Abstract: An automatic deviation control circuit for an angle modulated data transmitter is disclosed wherein the deviation level of modulated data is controlled by a modulation cancelling deviation error detection feedback loop. After the modulation is cancelled from a sample of modulated carrier by a predetermined value of deviation, residual modulation is detected, sampled following a predetermined number of like-level data bits, and applied to the modulation path gain to increase or decrease the deviation such that the residual modulation is minimized.

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: In an AM stereo system wherein a low frequency pilot tone is added to the difference channel signal before modulation of the carrier, "image shifting" and audio distortion in a receiver, due to residual pilot tone signal, are removed by separating out a portion of the pilot tone after it has been filtered and phase shifed for enabling the stereo mode of operation. The separated signal is then inverted and delayed appropriately for each of the PLL and audio circuits.

Abstract: An improved portable battery powered electrical device is disclosed which includes a battery pack having normally inactivated battery terminals so that inadvertent short circuiting thereof will not produce an undesirable high amplitude short current thereacross. A normally open switch interrupts the current path in the battery pack which is actuated to energize such battery terminals only when the battery pack is fully interconnected and mated to the associated portable housing. Fuse means are included to prevent the use of unauthorized battery packs without the foregoing safeguard provisions.

Abstract: A method and corresponding apparatus for maintaining constant bandwidth over a frequency spectrum in a microwave, dielectric resonator waveguide filter. Bandwidth is determined by the product of the resonant center frequency and the interresonator coupling coefficient. To maintain constant bandwidth while changing center frequency, the interresonator coupling coefficient must be chosen such that it varies inversely with changes in center frequency. The interresonator coupling coefficient is a function of the physical dimensions of the waveguide and the dielectric resonators, the dielectric constant and the spatial location of the resonators within the waveguide. Once the physical and spatial parameters have been established, the center frequency of the filter may be adjusted by altering the thickness of the resonators without changing the filter bandwidth.

Abstract: A method and corresponding apparatus for maintaining constant bandwidth over a frequency spectrum in a microwave, dielectric resonator waveguide filter. Bandwidth is determined by the product of the resonant center frequency and the interresonator coupling coefficient. To maintain constant bandwidth while changing center frequency, the interresonator coupling coefficient must be chosen such that it varies inversely with changes in center frequency. The interresonator coupling coefficient is a function of the physical dimensions of the waveguide and the dielectric resonators, the dielectric constant and the spatial location of the resonators within the waveguide. Once the physical and spatial parameters have been established, the center frequency of the filter may be adjusted by altering the thickness of the resonators without changing the filter bandwidth.

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 interdigital microstrip transmission line filter (100) includes three electrically conductive strips (104, 106 and 108) each coupled to grounded portions (110 and 120) on one end and coupled to respective capacitive loading pads (112, 116 and 114) on the other end. Input and output pads (130 and 140) may be coupled to signals from other circuitry located off or on the same substrate (150). Grounded portion (110) extends between capacitive loading pads (112 and 114) for minimizing undesired coupling between non-adjacent strips (104 and 108). As a result, the unique microstrip filter (100) has a frequency response that is substantially devoid of passband transmission zeros.

Abstract: An improved adaptive loop filter for modulatable frequency synthesizers containing digital phase comparators is described. The unique adaptive loop filter provides a wide bandwidth during a signal acquisition mode and a narrow bandwidth during a signal tracking mode. The adaptive loop filter includes a current limiter coupled to the error signal from the digital phase comparator for generating a current-limited output signal; a filter coupled by a resistor to the current limiter output signal and including a series-coupled resistor and capacitor for filtering the current limiter output signal to provide a steering line voltage; an amplifier coupled to the junction between the filter resistor and capacitor for generating a feedback signal; a resistor for coupling the feedback signal to the current limiter output signal for substantially reducing the duration of voltage transients; and a reference filter for coupling the steering line voltage to the steering input of a voltage-controlled oscillator.

Abstract: A data communications system is described that covers a geographic area divided into a plurality of non-overlapping zones and includes a general communications controller (GCC), a plurality of channel communications modules (CCM) and associated transmitters and receivers, and a plurality of portable radios. Message signals carrying alphanumeric information are communicated between the GCC and the portable radios by way of a radio channel. Each CCM takes a signal strength measurement every time it receives a message signal from a portable radio. The GCC gathers the signal strength measurements from the CCM receivers receiving the same message signal and computes an adjusted signal strength for each zone. The GCC then selects the zone having the largest adjusted signal strength for determining the location of the portable radio that transmitted the message signal.

Abstract: A synthesizer radio frequency (RF) signal receiver (FIG. 1) for single sideband radios is described that can eliminate interference due to internally generated spurious signals, commonly referred to as "whistler spurs". The unique receiver includes first and second mixers (102 and 106), which are intercoupled by a 75 mHz crystal filter (104) having a 20 kHz passband, and which are each coupled to signals from voltage controlled oscillators (120 and 140). The first IF frequency provided by the first mixer (102) varies about 75 mHz, and the second IF frequency provided by the second mixer (106) is fixed at 11.4 mHz. The second mixer (106) is coupled to 11.4 mHz stages (108) which have a 2.7 kHz passband. The 11.4 mHz stages (108) are followed by another mixer (110) and audio stages (112) for demodulating audio signals from the received RF signal, which are then applied to a speaker (114).

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 digital communication system including an encoder and decoder for the transmission of digital information over a transmission medium, the system having automatic frame synchronization and error correction requiring a minimum of tansmission bits and decoding time. The encoder processes a data stream and generates a transmission bit stream of N bits using convolutional encoding, autosynchronization sequence combining, and bit interleaving. The multi-phase sequential decoder decodes the received coded data, corrects transmission errors and automatically achieves frame synchronization from P selected phases of the received data. This is accomplished by selecting the phase of the received data with the best metric, bit de-interleaving, removing the autosynchronization sequence and comparing the received data of the selected phase with the extended code word subsets from the node having the best metric.