Rca Inc.

Rca Licensing Corporation

John J Gibson

Todd J Christopher

Michael D Ross

Frank B Lang

A variable preemphasis/deemphasis network is disclosed which is coupled between audio input and output terminals. The network exhibits a family of transfer function response characteristics which vary between a full deemphasis characteristic H(f) and a full emphasis characteristic 1/H(f) in response to a control signal and exhibits complementary transfer function response characteristics in response to reciprocal valued control signals. The network includes a signal filter which determines the shape of the transfer function response characteristic, and a gain controlled amplifier which determines which one of the family of transfer function response characteristics is exhibited in response to the control signal.

Variable preemphasis/deemphasis network

A circuit for separating FM signals from a composite signal utilizes a comb filter having successive frequency response nulls which span the frequency spectrum of the FM signal to be separated. The comb filter response is phase linear and defines the pass-band of the desired signal. A nonideal or phase nonlinear bandpass filter can be cascaded with the comb filter to attenuate out of band signals. The cascade combination of the comb filter and nonlinear bandpass filters is a cost effective substitute for the conventional, complicated phase linear bandpass filter having a boxcar frequency response traditionally used to separate FM signals.

Low distortion filters for separating frequency or phase modulated

A companding system for a television audio apparatus includes a compressor and an expander for stereo difference signals. The compressor provides variable preemphasis of high frequency signal components and the expander provides complementary variable deemphasis. At the receiver, unwanted signals are generated by a mixer that demodulates the stereo difference signal. The unwanted signals can cause mistracking of the expander relative to that of the compressor. A filter to eliminate the effect of these unwanted signals is placed in the expander control circuit, rather than the difference signal path. This eliminates the need and expense of an equalizing filter in the sum signal path.

Filter arrangement for an audio companding system

An FM signal is demodulated by the technique of sequentially sampling the signal and combining the samples to approximate the standard formula for the instantaneous frequency deviation ##EQU1## where the dots indicate the first derivative of the samples. The FM signal is assynchronously sampled at approximately four times the carrier frequency rate. Alternate samples are substantially equivalent to orthogonal components x and y of the FM signal. At least four successive samples are successsively stored so that at least four of the lastmost samples are always available for processing. Particular x samples are summed to create averaged samples x.sub.n and differenced to create approximations of derivatives x.sub.n of the x signal components and particular y samples are similarly summed and differenced to create averaged values y.sub.n and derivatives y.sub.n. These values are used in the equation for F.sub.n. In terms of successive samples, S, the equation for F.sub.n becomes

Demodulator of sampled data FM signals from sets of four successive

Under certain conditions a video disc player can be responsive to externally applied interference signals to provide a defect in the display of the information recovered from the disc. Apparatus is provided between the pickup circuits and the normal defect compensation apparatus of the player to detect the presence of the external signals and to activate the normal defect compensation apparatus. The apparatus includes a product generator which multiplies the combined extraneous signal and normally recovered signal with an amplitude limited version of the same signal in order to enhance the probability of detection of extraneous signals even when the amplitude thereof is small relative to the normally recovered signal.

Video disc player with RFI reduction circuit including a signal product

In a video disc system, geometric variations are recorded on the surface of the record and are representative of recorded picture and sound information. In a video disc playback apparatus for recovering picture and sound information from such a prerecorded record, a playback stylus is utilized to detect the geometric variations. Sound interference in the video signals may be produced by the non-linear characteristics of the playback stylus. A non-linear aperture correction circuit interposed between the playback stylus and the demodulator circuitry of the playback apparatus effects a substantial control of the intermodulation products.

Non-linear aperture correction circuit

In a video disc playback apparatus, a playback stylus is utilized for the recovery of information from prerecorded disc records. In one system, geometric variations are recorded on the surface of the record and are representative of recorded picture and sound information. As these geometric variations pass beneath the stylus, the capacitance between the stylus electrode and the surface of the disc varies in accordance with the recorded representations. The capacitive variations are converted to electrical signal variations in the playback apparatus. In such a video disc playback apparatus, sound interference in the video and video interference in the sound can be produced by the non-linearity of the aforementioned pickup stylus. Use of a non-linear aperture corrector between the pickup circuitry and the demodulator circuitry of the playback apparatus reduces these interferences.

Video disc playback apparatus with non-linear aperture correction

An antenna system particularly suitable for permitting low cost reception of broadcasted circularly polarized television low and high VHF signals is provided by arranging all of the broadcast antennas so that the low and high VHF television frequency signal waves are radiated in opposite directional senses of circular or elliptical polarization. The low cost receiving antenna for receiving both of these bands comprises a pair of linear elements with the first of the pair of elements adapted to receive linearly polarized waves in a first linear polarization and a second of the elements adapted to receive linearly polarized waves in a second orthogonal polarization. A combining means includinga delay is provided for combining the signal waves received at one of the pair of elements with delayed signal waves received at the other of the receiving elements where the delay is on the order of one-quarter wavelength at a frequency within the low VHF frequency band.

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Princeton, NJ, United States of America

John J Gibson