Abstract: The present invention provides error checking for data dependent coding circuitry which checking is complicated by a considerable amount of circuitry which is activated only when the incoming data conforms to specific requirements (i.e., three or more consecutive logic zeros). Except for these occurrences, the output from the coding circuitry is straightforward representation of the nonreturn to zero input data. The present invention uses a straightforward detecting circuit to normally pass the data and a data compare circuit which compares the output of the detector with the output of the data dependent circuitry except for times when the specific condition of three consecutive logic zeros occurs. At that time, the data compare circuitry checks to make sure that both the code detector and the encoding circuit have detected the occurrence of this condition.

Abstract: An auto-equalizer for passing data pulses of the type which tries to restore the relative amplitude of the first and third harmonics of the data signal frequency while deemphasizing the amplitude of other higher harmonics. The present invention accomplishes the relative harmonic amplitude restoration by controlling the resistance in a tuned circuit element affecting the gain of a signal passing amplifier. The adjustment of the resistance directly affects the Q of the tuned circuit involved.

Abstract: A low power consumption, compact portable stereo radio transmitter and a receiver therefor, the transmitter having two audio processing channels each for receiving inputs from two stereo pickup stations and including amplifier circuits with selector switches providing a mode of even harmonic generation, a mode of odd harmonic generation, and a mode of undistorted amplification, a 38 KHz oscillator, flip flop coupled to the oscillator to provide a 19 KHz pilot signal, a difference amplifier and a balanced mixer to produce a double-sideband suppressed carrier signal centered on 38 KHz, and an amplifier for combining the balanced mixer output, the pilot signal and the two channel output and modulating a carrier signal. The receiver includes amplifier, detector, and decoder circuitry to receive the radio signals from the transmitter and produce stereo audio signals for driving a standard stereo amplifier.