Abstract: A point of sale terminal is disclosed that provides all of the usual point of sale terminal functions, but that is entirely field portable. Data pertinent to each purchase can be input to the terminal via a keyboard assembly, a touch-screen display or a signature-capture screen assembly, or via an antenna and radio link from an associated bar code scanner. Data may be communicated at any time to a remote host computer, also via a separate antenna and radio link. The communication links with the host computer and the bar code scanner operate independently and simultaneously, using mutually compatible modulation schemes such as a spread spectrum scheme for the host computer link and a narrowband or spread spectrum scheme for the bar code scanner link. The terminal thereby functions as a portable repeater or node in a data communications network.

Abstract: A point of sale terminal is disclosed that provides all of the usual point of sale terminal functions, but that is entirely field portable. Data pertinent to each purchase can be input to the terminal via a keyboard assembly, a touch-screen display or a signature-capture screen assembly, or via an antenna and radio link from an associated bar code scanner. Data may be communicated at any time to a remote host computer, also via a separate antenna and radio link. The communication links with the host computer and the bar code scanner operate independently and simultaneously, using mutually compatible modulation schemes such as a spread spectrum scheme for the host computer link and a narrowband or spread spectrum scheme for the bar code scanner link. The terminal thereby functions as a portable repeater or node in a data communications network.

Abstract: A frequency shift keying modulating circuit produces a first frequency according to a surface acoustic wave transducer natural resonant frequency and a second frequency according to the surface acoustic wave in combination with a reactive element. The frequency selected is determined by the state of a PIN switching diode in parallel with the reactive element.

Abstract: A point of sale terminal is disclosed that provides all of the usual point of sale terminal functions, but that is entirely field portable. Data pertinent to each purchase can be input to the terminal via a keyboard assembly, a touch-screen display or a signature-capture screen assembly, or via an antenna and radio link from an associated bar code scanner. Data may be communicated at any time to a remote host computer, also via a separate antenna and radio link. The communication links with the host computer and the bar code scanner operate independently and simultaneously, using mutually compatible modulation schemes such as a spread spectrum scheme for the host computer link and a narrowband or spread spectrum scheme for the bar code scanner link. The terminal thereby functions as a portable repeater or node in a data communications network.

Abstract: A transceiver has an RF oscillator stage shared by the receiving and transmitting modes. The RF oscillator has a feedback loop incorporating a SAW delay line. A switching arrangement selectively couples the antenna to the transmission circuit and optionally couples the antenna to the receiving circuit. The RF oscillator stage is isolated from switching perturbations by small capacitors at the input and at the output of the oscillator.

Abstract: A circuit is provided which gauges the amount of significant high-frequency spectral energy in the very recent history of the program material and ignores the effects of short noise bursts and other transients associated with FM reception in the moving vehicle. The circuit provides an output voltage which can be used to adjust the attack characteristics of an audio processor.

Abstract: A closed-loop attenuator for an FM stereo receiver provides attenuation to the L+R audio signal in a controlled and predictable reaction to an ultrasonic noise (USN) voltage presented to an input amplifier. This is accomplished through a closed-loop circuit configuration including a multiplier which modulates the current output of the input amplifier in accordance with the output of a master differential amplifier and supplies the modulated current to a gain stage connected to the input of the master differential amplifier. The output of the master amplifier is mirrored by a slave differential amplifier which applies the actual audio signal attenuation. The closed-loop configuration confines this linear control action to a very narrow range. Outside of this range, the circuit provides either full attenuation or no attenuation.

Abstract: An audio processor for adaptively rejecting undesired noise and interference in an audio input which includes a variable Q, 10 kHz switched capacitor notch filter. The Q of the notch filter is varied by a control loop responsive to the 10 kHz content of the audio signal. The notch filter includes a summer section that is clocked at a predetermined frequency, and an integrator section which is clocked at a multiple of the predetermined frequency in order to prevent center frequency variation with changes in Q of the notch filter.