Abstract: A radar system alternately transmits relatively short and long pulses. The video signals corresponding to the target returns from consecutive pulse transmissions are converted to digital format and then integrated except that radar return signals from targets within a first range resulting from long pulse transmissions are not used for integration.

Abstract: A linear sweep frequency modulator for a varactor tuned transistor microwave oscillator used in an FM/CW radio altimeter where the oscillator-frequency v. varactor bias characteristic is non-linear. A linear triangular wave is converted by means of a function generator to the non-linear wave required for varactor bias to cause linear frequency modulation of the oscillator. Linearity of modulation is tested by measuring variations in the period of a calibration signal derived from a delay line. Variations in the period of the calibration signal are measured by determining the difference between the average and the instantaneous calibration period and sampling the difference during each cycle of the triangular wave, once during the upswing thereof when the oscillator is at low frequency and once during the down swing thereof when the oscillator is at high frequency and separately integrating the up swing and down swing samples.

Abstract: A combustible gas detection system in which remotely located combustible gas sensors of the analog type are monitored by a central controller. The sensor analog data is converted to digital data and transmitted to the controller. The controller tests the integrity and validity of data received from the sensor, identifies the nature of any faults therein and vocally signals the cause of such faults. The controller computes the concentration of combustible gas at the sensor and automatically determines sensor calibration constants from received sensor data.

Abstract: The output frequency of a phase locked loop frequency synthesizer is measured by a counter which counts whole output cycles and a timer providing a signal proportional to a fractional output cycle during a sampling period. The counter output is stored into a latch at each sampling period. Calculated frequency is generated by an accumulator which is incremented a selectable integer N at the completion of each sampling period. The accumulator output is divided into a first part relating to whole cycles and a second part relating to fractional cycles. An adder takes the difference of the latch stored number and the accumulator output first part. The resulting difference, with the accumulator output second part restored thereto, comprises a coarse error signal in digital form. The digital coarse error signal is converted to analog and applied as one input to a summer. A second input to the summer is provided by the timer signal after being scaled proportionately to N in a multiplying D/A converter.

Abstract: An ion mobility detector has dual drift regions respectively on either side of a centrally located reaction region and respectively separated therefrom by dual shutter grids. Each drift region terminates in a Faraday cup. An ion accelerating electrical field gradient is provided between the Faraday cups so that negative ions are drawn into one drift region and positively charged ions are drawn into the other drift region.

Abstract: An improved oxygen sensing cell, especially of the polarographic type, is intended for use primarily in a gaseous environment. The cell has a cathode located at the bottom of the cell body. The cathode comprises a gold mesh electrode laminated to a thin-film sense membrane. The electrode is thus made immobile relative to the membrane, thereby improving the response time and providing for long-term sensor stability. The cell further has a guard electrode for the cathode. The guard electrode operates continuously and scavenges any oxygen molecules which are dissolved in the electrolyte and diffused towards the cathode. As a result, the dynamic range of the cell is substantially increased. The anode comprises a silver wire wound about a spool retained within the main cavity in the cell body. A p.c. board, as well as a compensation membrane, are resiliently retained at the top of the cell body. The body carries conductors for electrically connecting the p.c.

Abstract: A radio altimeter of the FM/CW type which is linearly frequency modulated by a triangular wave exhibits step error in the output indication at times near the peaks of the modulating wave. Step error is eliminated by gating the data which is processed to produce the altimeter output indication to inhibit processing during times the modulation wave is near peak values and to enable processing at other times. Accuracy is further improved by adjusting the duration of the time during which data processing is enabled so as to equal an integral number of cycles of processed data.

Abstract: A surface acoustic wave convolver (10) with parabolic horns (16, 18), a typical horn (16) having a compensating stub (16a) at the horn input end (16b) disposed centrally on the horn longitudinal axis (19) to maintain the phase coherence at the horn output end Z(16c) of a wave traversing said horn (16).

Abstract: A filter for tracking the ground signal return in an FM/CW radio altimeter. The filter has a variable band pass frequency response which is adjusted as a function of the altitude measured by the altimeter. The control means of the filter respond to altitude measurements in digital format.

Abstract: A beam forming network for a circular array antenna includes a sum pattern network for generating signal weights corresponding to a sum antenna pattern having omnidirectional sidelobes and a difference pattern network for generating signal weights corresponding to a difference antenna pattern with omnidirectional sidelobes. Means are provided to couple energy from the difference pattern network to the sum pattern network. The signal weights are split by signal splitters and delivered in pairs to output terminals, one of which is terminated in its characteristic impedance.

Abstract: A combustible gas detection system in which analog signals produced by a remotely located combustible gas sensor are converted to digital signals at the sensor and the digital signals control a coherent frequency shift keying modulator which impresses alternating signal currents, through an optically coupled isolator, on a transmission line connecting the sensor with a control station. The transmission line is a two wire link of ordinary quality which carries power from the controller to the sensor as well as signals from the sensor to the controller.

Abstract: An alarm modification kit for adding an electrical alarm signal feature to a mechanical recording type meterorological instrument. The kit includes a counterbalanced shutter arm adapted to be secured to the output shaft of the instrument which carries the recorder pen without disturbing the output shaft in its mountings. The free end of the shutter arm is T-shaped with a notch located centrally therein. A U-shaped photo source-sensor assembly is adjustably positioned astride the free end of the shutter arm so that the cross member of the arm moves transversely between the legs of the source-sensor, preventing generation of an electrical signal therefrom until the notch of the shutter arm is moved into alignment with the source-sensor.

Abstract: An antenna element is comprised of two rectangular microstrip patch dipoles spaced by dielectric a predetermined distance above a ground plane conductor. One edge of each dipole is electrically shunted to the ground plane conductor. The dipole feedpoints are separated by a quarter wavelength of the antenna resonant frequency. An isolated power splitter and phase shifter connects an antenna element port with the dipole feedpoints so that the signal at one feedpoint lags the signal at the other feedpoint by 90.degree.. The antenna element will end fire through the dipoles in the direction of the lagging signal feedpoint.A low profile circular array antenna is comprised of eight such antenna elements arranged on the ground plane conductor equally spaced with their phase centers on a common phase center circle.

Abstract: A thin film metallic loop is used to electrically short the gap between metallic portions of a surface acoustic wave device to eliminate substrate surface cracks. The loop is deposited on the substrate at the same time the structures defining the gap are deposited.

Abstract: In an amplitude modulation radio receiver a relatively narrow band filter is placed before the receiver detector and a relatively wide band filter is placed just prior to the IF amplifier stages. An IF stage controlled by receiver AGC is designed to have a saturation or clipping level about 6 dB above the normal IF level for that stage. As a result the selectivity characteristic for the receiver will be approximately rectangular and encompass the IF frequency channel if the bandpass of the narrow band filter is chosen to be the IF frequency channel.

Abstract: An electronic package is mounted by its leads in an inner hermetically sealed package in an atmosphere of dry nitrogen gas at about 50 torr gas pressure. Leads extend through hermetically sealed electric feedthroughs into an outer enclosure which is maintained at a vacuum of at least 1.times.10.sup.-4 torr. Electrical leads which extend substantially the entire length of the interior space of the outer enclosure pass out of the outer enclosure at first ends of the leads through hermetically sealed electrical feed-throughs and at second ends electrically communicate with and structurally support the leads from the inner enclosure so that the inner enclosure is disposed between the first and second ends. The surfaces of the inner enclosure and the interior surface of the outer enclosure are electropolished.The electronic package consists of a central core sandwiched between beryllium oxide heat spreaders on which are mounted heaters in the form of power transistors.

Abstract: The ion accelerator for an ion mobility detector cell is comprised of a ceramic tube coated inside with a thick film resistor composition across which a voltage potential difference is impressed to provide an ion accelerating electrical field gradient within the tube.

Abstract: A portable battery powered pump providing constant mass flow of air sample through a particular filter or vapor trap in which the pump drive motor speed is controlled by an amplifier having a reference voltage input and an inverse feedback signal related to sensed motor speed. Compensation for increased resistance to air sample flow is made by a motor current feedback signal applied to the amplifier to cause motor speed to increase with increased flow resistance.

Abstract: A tube closed at the end by plugs having axial bores therein and which support a hollow, porous walled cylinder concentrically within the tube to form a conduit interconnecting the plug bores while allowing a clearance space between the cylinder outer wall and the tube inner wall. A combined ejector-blowback valve is secured to one plug externally of the tube for inducing gas flow through the plug bores and cylinder in one valve position and for reversing flow through the plug bores and cylinder in a second valve position to dislodge and discharge adherent material. The probe is mounted with the end opposite the ejector-blowback valve extending into the gas stream to be sampled. Gas samples are withdrawn from the clearance space surrounding the cylinder. The probe is constructed substantially entirely of corrosion and temperature resistant ceramic material.

Abstract: An ion mobility detector in which selectivity and sensitivity is enhanced by converting through surface interactions sample gas or vapor to a form more readily ionized or by converting through surface interactions interferent gas or vapor to a form less readily ionized. To accomplish the conversion, samples may be passed through a catalytically reactive filter prior to injection into the detector reaction region; exposed to a reactive coating placed on the surface of a permeable membrane prior to diffusion therethrough into the reaction region or exposed to a reactive coating placed on the interior walls of the reaction region.