Abstract: A thin film magnetic record/playback head having suitably thin layers of soft, high permeability magnetic material, such as permalloy, electrically insulated from each other by very thin layers of a magnetic material having suitably high resistivity, such as NiZn ferrite. The improved magnetic record/playback head is capable of reading and writing much higher bit densities (up to about 100 kfci) and at much higher frequencies (100 MHz or higher) than prior art devices while remaining fully compatible with existing electronic circuitry.

Abstract: A multitrack head assembly has a plurality of magnetic heads arranged side-by-side along a transducing gap line extending across an upwardly facing tape-engaging surface which includes a series of elongated coplanar ribs alternating with low-pressure channels on both sides of and orthogonal to the gap line. For continuous in-contact recording, each rib is aligned with a particular one of the magnetic heads and has a width that is greater than the width of the transducing gap of the head with which it is aligned; furthermore, each rib has a gently curved tape-engaging surface with a radius of curvature R.sub.1 in a direction orthogonal to the gap line and a radius of curvature R.sub.2 in a direction substantially parallel with the gap line, where R.sub.1 and R.sub.2 are not necessarily the same.

Abstract: Data deskewing apparatus includes two, byte organized random access memories for storing, aligning and then reading out channels of data which were originally skewed when read in from a multitrack magnetic recorder system. While write-in operations on skewed data are taking place in one of the random access memories (RAM), read-out operations on skew-corrected data, which had been written in on the previous cycle, are taking place in the other RAM. On the completion of a write in/read out cycle, the roles of the RAM's are interchanged, and the process repeated.

Abstract: An MR head includes two substantially identical MR elements, separated by a thin film non-magnetic electrically conductive spacer. A current applied to the MR head splits into two respective substantially equal currents that flow in the same direction through the substantially identical MR elements, to provide mutual bias and to serve as sense currents for detecting change in element resistance. The MR elements are biased to operate in a magnetically unsaturated mode. This results in a "bootstrapping" of short wavelength signals that effectively amplifies the reproduced signal over a broad region of the signal spectrum when the linear spacing between the MR elements is in the range of from one half to one times the half-wavelength of signals recorded on a magnetic recording medium.

Abstract: An array of an odd number of alternatingly polarized permanent magnets of equal pole strength, disposed in side by side relationship, provides a spatially varying magnetic transfer field for a master and slave tape wrapping a rotatable capstan. First and second terminator magnets, located, respectively, at opposite ends of the array, are similarly polarized with respect to each other, but opposite the polarization of the end magnets of the array. Furthermore, each terminator magnet has a magnetic moment that is less than the magnetic moment of each magnet in the array. Each terminator magnet serves (1) to suppress stray magnetic fields associated with the corresponding end magnet in the array, and (2), in combination with the odd number of alternatingly polarized magnets in the array, to suppress DC residual magnetization in the slave tape.

Abstract: Compensation for space charge build-up in an electro-optic modulator device is realized by recurrently recalibrating the device. During each recalibration interval, light transmitted through the device is intercepted and converted to an electric signal which is compared to a test signal of a magnitude corresponding to light of an intensity that would be transmitted through the device in the absence of space charge. The difference between the respective magnitudes of the test signal and the electric signal serves as a bias to supplement the normal modulating drive signal until the time of next recalibration. Recurrently, but at a rate lower than the recalibration rate, the device is short circuited, while flooded with light, to eliminate space charge build-up.

Abstract: A method of, and apparatus for, applying charge to a plastic, electrically conductive sheet having an image formed thereon by a photocopier, to neutralize the buildup of electrostatic charge on the plastic sheet. The amount of charge applied to the plastic sheet, to prevent electrostatic adhesion, is determined as a function of the amount of toner forming the image on the plastic sheet. According to one embodiment of the present invention, the amount of toner forming the image is determined as a function of the average transparency of the plastic sheet.

Abstract: Apparatus, for recording information on a flexible magnetic slave disk by contact transfer of information recorded on a flexible magnetic master disk, includes a U-shaped electromagnetic device terminating, respectively, in a first planar pole tip axially aligned with a second movably mounted planar pole tip, to define predominately a single closed-loop flux-conducting path extending through a contact-transfer zone between the pole tips. A linear actuator, coupled to the movable pole tip, serves for releasably mounting the master disk in intimate facing relationship with the slave disk in the contact-transfer zone between the planar pole tips. Control circuitry applies an alternating electrical signal to the U-shaped electromagnetic device to develop an alternating magnetic field in the closed-loop flux-contacting path that produces a corresponding alternating magnetic transfer field extending axially in the contact-transfer zone between the planar pole tips.

Abstract: A public switched telecommunications network including a beacon transmitter associated with a station in such network and transmitting periodic beacon signals containing information regarding the location of said beacon and station. A portable receiver is provided for receiving such information and reproducing such location information to permit the carrier of said receiver to locate said station. The location information may be visually or audibly reproduced. The station may be a public pay station and/or a cellular station. The receiver may be associated with a portable cellular transceiver for establishing communications with a cellular transceiver disposed adjacent the beacon.

Abstract: A magnetometer includes a magnetoresistive element and first and second high-permeable laminated flux collectors of height H partially overlapping, respectively, opposing lateral edges of the magnetoresistive element, wherein the flux collectors are separated laterally by a gap of length G which the magnetoresistive element spans. The two laminated flux collector and the magnetoresistive element cooperatively form an open-loop flux-conducting path of total height 2H+G, that is capable of collecting flux of a magnetic field being measured and, in response to the flux collected, developing a magnetometive force across the gap G that is functionally related to the height of the flux collectors.

Abstract: Electromagnetic drive circuitry, for recording information on a flexible magnetic slave disk by contact transfer of information recorded on a flexible magnetic master disk, includes a U-shaped electromagnetic device terminating, respectively, in a first planar pole tip axially aligned with a second movably mounted planar pole tip, to define a closed-loop flux-conducting path extending through a contact-transfer zone between the pole tips. The drive circuitry further includes signal-modulating circuitry for applying an alternating voltage of progressively decreasing amplitude to the electromagnetic device, to develop an alternating magnetic field of progressively diminishing strength in the closed-loop flux-conducting path that produces a corresponding alternating magnetic transfer field extending axially in the contact-transfer zone between the planar pole tips.

Abstract: In formatting a digital data stream for interleaved recording with included resynchronization sequences inserted into the data stream, rather than recurrently recording the resynchronization sequences at the boundaries of the interleave blocks or recording many resynchronization sequences throughout the data, the present invention teaches staggered recording of the resynchronization sequences throughout the page of interleaved code words in a pseudo-random fashion. This staggering of the resynchronization sequences throughout the interleave blocks "randomizes" the errors due to tape drop outs so that errors are more uniformly distributed among the positions in the code words, and attendantly, are more likely to be correctable.

Abstract: An electro-optic light modulator of the type including a body of an electro-optic material having opposed surfaces and a pair of planar conductive electrodes on at least one of the surfaces of the body. Polarity-reversing drive circuitry applies a voltage across the electrodes, the polarity of the voltage being reversed at a frequency of about 1 Hz or less with polarity reversal occurring either when the light modulator is turned off or when there is an insignificiant voltage drop across the electrodes. This low frequency of the reversal of the polarity of the voltage substantially eliminates drift of the voltage-transmissivity of the modulator, lowers leakage, and reduces damage to the electrodes during a given period of time of operation.

Abstract: Apparatus, for preventing false recognition of one or more address marks arranged at predetermined locations in a stream of information-bearing bits played back from a record storage medium, such as a disk, includes a timer, synchronized with the bit stream, for defining a corresponding series of intervals or "windows" relating, respectively, to when each of the address marks is expected to occur in the bit stream. An decoder, responsive to the timer, signals which address mark is expected to occur during each interval defined by the timer. Validation circuitry, responsive to the bit stream, the timer and the decoder, determines whether each address mark expected actually occurs in the bit stream within the corresponding time interval defined by the timer.

Abstract: The present invention comprises the hardware implementation of an algorithm for a run length limited (1,7) block code of rate 2/3, wherein 2 unconstrained bits are mapped onto 3 constrained bits. The encoded data stream has a minimum of 1 "zero" between adjacent "ones", and a maximum of seven "zeros" between adjacent "ones". Unlike earlier (1,7) block encoders, the encoder of the present invention is a 4 state machine whose internal state description requires only 2 bits, rather than the 3 bits as taught in the prior art. The 4 state encoder combines the 2 incoming data bits with present state information to generate the output encoded sequence, and the next state designation. Error propagation due to a single channel bit error is limited to 5 bits.The decoder of the invention utilizes three, 3 bit shift registers which hold 9 bits of the encoded data; each group of three bits is decoded into 2 bits corresponding to the original input bits by means of a logic array fed from the three shift registers.

Abstract: A bi-directional magnetic head assembly comprises a first write head adjacent to a read head, adjacent to a second write head. The three heads are in-line, so that the tape engages one or the other write head followed by the read head for either direction of tape motion. The central read head has slots on either side of its transducing region for skiving of entrained air and debris from the tape before the tape engages the transducing element of the read head for either direction of tape travel. On the other hand, each write head has only a single slot for skiving entrained air and debris; a slot being located in each write head structure outboard from the write transducing gap. In reading while writing during bi-directional operation, the write head first approached by the tape for a given direction of motion is the active, writing head. Because the slot is on the outboard side of each write head structure, skiving action occurs prior to the tape reaching the active write transducing gap.

Abstract: In order to diminish the effects of debris on recording and playback in a cartridge loaded recorder, adhesive material is placed inside the enclosed magnetic tape cartridge. The adhesive is placed on appropriate interior walls and other available surfaces of the cartridge, and is covered by a protective screen having holes through which the debris may pass. The size of the holes is large relative to the debris size. The adhesive material is located clear of the magnetic tape path, magnetic heads and guides, and if an inadvertent tape loop occurs in the cartridge, the protective screen insures that the magnetic tape cannot come into contact with the adhesive proper. Any losse debris, however, incident on the holes of the protective screen is captured and immobilized by sticking to the adhesive material.

Abstract: In the practice of the invention, a small magnet is attached to a slidable tab located on the leading edge of the cartridge. Before insertion of the cartridge into the recorder, the slidable tab is moved by the user to one of two positions. One position is the write protect position for inhibiting recording on the tape in the cartridge, and the other position permits recording on the tape. The associated recorder has two side by side Hall effect sensors. When the cartridge is positioned in the recorder, the magnet, depending upon the selected position of the cartridge tab, is directly opposite to, and activates, only one or the other Hall effect sensors. If no cartridge is in the recorder, neither Hall effect sensor is activated, indicating that no cartridge is in place. If the cartridge is in the recorder, and if the first sensor is activated, then the write protect circuit of the recorder is energized. If the second sensor is activated, then writing on the tape is permitted.

Abstract: In a capstanless tape transport, practice of the invention provides substantially constant tape tension when tape is spooled from a supply reel to a take up reel over the tape's entire length, for either direction of tape travel. The tape velocity is maintained constant by a closed loop velocity servo controlling the current applied to one of the reeling motors, and the tape tension is maintained substantially uniform by applying a current derived in an open loop manner to the other motor, such that the sum of the currents to the two reeling motors equals a constant.The invention may be implemented either utilizing analog control or digital control of the reeling apparatus.