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Showing papers on "Stub (electronics) published in 1980"


Journal ArticleDOI
TL;DR: The transmission-line modelling method presents a new approach to the solution of lumped networks by providing discrete models for components and the concept of numerical parasitic components as a means of assessing errors is introduced.
Abstract: The transmission-line modelling (t.l.m.) method presents a new approach to the solution of lumped networks by providing discrete models for components. Errors become due to the modelling process only and not due to the approximate solution of an approximate calculus model. The correspondence between stub models and existing implicit methods is shown and the concept of numerical parasitic components as a means of assessing errors is introduced. The paper then describes the entirely new explicit routines resulting from transmission-line modelling and explains their use in non-linear circuits. Finally, examples of mixed implicit and explicit working are given for the solution of non-linear transistor circuits.

154 citations


Journal ArticleDOI
TL;DR: In this paper, a half-moon microstrip radial transmission line circuit element with a 180/spl deg/ circular stub or "half-moon" structure, having a reflection coefficient of unity magnitude and phase which varies slowly with frequency is presented.
Abstract: A microstrip radial transmission line circuit element namely a 180/spl deg/ circular stub or "half-moon" structure, having a reflection coefficient of unity magnitude and phase which varies slowly with frequency is presented. Theoretical reflection coefficient data are shown to agree well with experimental microstrip (epsilon/sub r/=2.35, h =250 mu m) data in X band. Applications of the half-moon microstrip element in the design of broad-band bias or tuning networks are discussed.

44 citations


Journal ArticleDOI
TL;DR: In this article, the design of three types of loaded-line p-i-n diode digital phase shifter circuits is presented, and the three configurations considered are 1) main line mounted, 2) stub mounted, and 3) switchable stub length.
Abstract: The design of three types of loaded-line p-i-n diode digital phase shifter circuits is presented. The three configurations considered are 1) main line mounted, 2) stub mounted, and 3) switchable stub length. Expressions for various design parameters are derived. Calculations show that for the 22.5/spl deg/ phase bit the maximum bandwidths for three circuits are 22.7, 19.2, and 18.4 percent, respectively. Starting from the p-i-n diode parameters, optimum designs of these circuits for obtaining minimum insertion loss, maximum bandwith, and minimum size are also discussed. It is found that the switchable stub length type configuration is suitable when nearly ideal p-i-n diodes are used while stub mounted type configuration is suitable for nonideal diodes. Experimental and theoretical performance (bandwidth and insertion loss) of stub mounted type circuits are compared and found to be in good agreement.

40 citations


Journal ArticleDOI
L.Y. Chow1
TL;DR: The 3-D Green's function is constructed based on the same image model of charges and currents as in 2-D, and the imaginary part of the input impedance agrees with that calculated from the TEM approach.
Abstract: A spatial Green's function in 2-D for straight and infinite microstriplines has been shown to be accurate at frequencies that the dynamic effects cannot be neglected. It is reasonable, therefore, to expect that a similarly accurate spatial Green's function in 3-D can be constructed for finite and curved microstriplines. Based on the same image model of charges and currents as in 2-D, this paper constructs the 3-D Green's function. The Green's function is then applied, through Harrington's moment rnethod, to calculate the input impedance of a few microstriplines, viz., a matched microstripline, straight and hairpin open-ended stubs. The input impedance of a microstrip stub always has a small resistive component indicating the radiative loss. This resistive component agrees with that calculated from the Lewin's formula. Finally, as expected, the imaginary part of the input impedance agrees with that calculated from the TEM approach.

36 citations


Journal ArticleDOI
TL;DR: In this article, a theory for dielectric-filled edge-slot (DFES) antennas is developed for conformal mounting on conducting bodies of revolution (BOMs).
Abstract: A theory has been developed for dielectric-filled edge-slot (DFES) antennas which belong to a class of circumferential slot antennas that are suitable for conformal mounting on conducting bodies of revolution. The specific antenna considered consists of a disk of dielectric substrate mounted between the two halves of a conducting cylinder and is excited at its center by a coaxial stub. It can be tuned for a desired operating frequency with the help of a number of axially oriented passive metallic posts located inside the dielectric region. For analysis, the antenna is modeled as a symmetrically excited E -type radial waveguide loaded with the metallic posts and terminated by an equivalent admittance appropriate for the radiating aperture. Circuit parameters for the metallic posts in the radial waveguide are obtained by detailed field analysis using mode matchng techniques. These are then used, along with the equivalent transmission line circuit for the antenna, to obtain the input reflection coefficient as a function of frequency for various DFES antennas. The results of computations based on the theory developed are compared with available measured values.

33 citations


Patent
Gens Tore Teodor1
08 Feb 1980
TL;DR: In this paper, an arrangement for attaching a tank fitting to a plastics fuel tank for motor vehicles is described, in which an elastic sleeve is clamped whose inner end by means of an inner clamping means sealingly engages against the fitting, and whose outer end is folded over outwardly and pressed sealingly against the pipe stub.
Abstract: An arrangement for attaching a tank fitting to a plastics fuel tank for motor vehicles. Through an outwardly directed pipe stub in the tank wall the fitting is inserted and fastened to the tank. Between fitting and pipe stub an elastic sleeve is clamped whose inner end by means of an inner clamping means sealingly engages against the fitting, and whose outer end by means of an outer clamping means surrounds the pipe stub. The inner clamping means is part of a stiffening member bearing against the inside of the pipe stub by means of an upper support ring. The outer end of the sleeve is folded over outwardly and pressed sealingly against the pipe stub by means of the outer clamping means and aganist the reinforcing action of the stiffening member. The arrangement enables a simple and sealed attachment of heavy tank fittings, e.g. a fuel pump.

17 citations


Patent
Tomoki Uwano1
03 Jun 1980
TL;DR: In this paper, a simple capacitive susceptance stub is connected to the transmission line near the coupling point of the resonator, which is used to adjust the load impedance of the oscillator.
Abstract: A solid-state MIC oscillator in the form of a planar transmission circuit has a band rejection filter as a load circuit of an oscillation device. The band rejection filter is a resonator coupled to a transmission line which connects the oscillation device with an oscillator load. The load impedance of the oscillation device is adjusted to the oscillating condition by the position of the resonator. A simple capacitive susceptance stub is connected to the transmission line near the coupling point of the resonator. Variation of the oscillator frequency characteristics versus temperature caused by variation of the oscillator load is improved in an excellent manner due to the provision of the simple capacitive susceptance stub.

17 citations


Patent
Leon C. Brown1, Stanley L. Pond1
30 May 1980
TL;DR: In this article, the spiral thread of a screw-like stub member mounted on the housing of a corona charging apparatus is engaged to change its position relative to a photoconductor surface.
Abstract: A corona wire, either directly or through an auxiliary element, engages the spiral thread of a screw-like stub member mounted on the housing of a corona charging apparatus to provide a simple, low cost and easily assembled corona wire adjuster. The stub member is mounted on the housing such that it may be rotationally driven much like a screw, but, unlike a screw, will not move into or out of the housing as it is rotated. Rotation of the stub member causes the corona wire to move in a direction parallel to the stub member axis in response to the thread engagement and thereby change its position relative to a photoconductor surface.

16 citations


Patent
06 Oct 1980
TL;DR: In this paper, a microstrip transmission line is constructed with a printed circuit board, the microstrip stub being short in comparison to the wavelength at the resonant frequency of the filter and assuming the characteristics of an inductive impedance.
Abstract: Impedance matching between a helical resonator of a helical resonator filter and a circuit connected thereto is accomplished by the provision of a microstrip transmission line including a microstrip stub printed on a printed circuit board, the microstrip stub being short in comparison to the wavelength at the resonant frequency of the filter whereby the microstrip stub assumes the characteristics of an inductive impedance. A first electrical end of the microstrip stub is connected to a first terminal of the helical resonator and to a first terminal of the circuit, and a second electrical end of the microstrip stub is connected to a second terminal of the helical resonator and to a second terminal of the circuit.

15 citations


Patent
17 Sep 1980
TL;DR: In this paper, a pole is raised vertically until its lowermost end portion is clear of the ground so that a lower end portion of the pole can be sized, as necessary, for reception by a mechanism joining the pole and stub.
Abstract: A method and apparatus for lengthening or shortening a pole supporting lines, such as electric power and telephone lines. The method includes the providing of a stub adapted to be joined in abutting end-to-end relationship with the lower end of the pole to form a lower extension and support for the pole. The pole is raised vertically until its lowermost end portion is clear of the ground so that a lower end portion of the pole can be sized, as necessary, for reception by a mechanism joining the pole and stub. If necessary, the length of the pole is also shortened to provide a desired combined length. After the lower end has been sized, the pole and stub are joined to each other so that they constitute, in effect, a substantially rigid continuation of each other. The pole and stub are then vertically lowered into the ground to a required depth and the ground is consolidated around the base of the stub. The apparatus includes appropriate structure for accomplishing the preceding method.

13 citations


Patent
07 Jul 1980
TL;DR: In this article, a microwave antenna is associated with an integrated amplifier and frequency converter circuit for operating frequencies of from 1 Ghz to 40 Ghz, and the circuit may be tuned by variation of a voltage regulated supply which is impressed onto the center conductor of a coaxial output cable.
Abstract: A microwave antenna has associated therewith an integrated amplifier and frequency converter circuit for operating frequencies of from 1 Ghz to 40 Ghz. The circuit may be tuned by variation of a voltage regulated supply which is impressed onto the center conductor of a coaxial output cable. The frequency selective tuning elements are strip lines etched on one side of a double sided printed circuit board. The receiver is designed as an integral part of a quarter spherical reflector which illuminates a resonant cavity in which a stub antenna is mounted. The stub antenna is also directly connected to an input transistor of the amplifier/converter circuit.

Patent
08 Apr 1980
TL;DR: In this article, an end-opening transmission line filter, which is short-circuited for the higher harmonic, is provided in the output side. But this filter cannot be used to eliminate a higher harmonic sufficiently.
Abstract: PURPOSE:To eliminate a higher harmonic sufficiently by providing an end opening transmission line filter, which is short-circuited for the higher harmonic, in the output side. CONSTITUTION:In case the length l of end opening stub 26 provided on the transmission line is l<1/4 wave length, the stub is capasitive; and in case of l=1/8 wave length, the susceptance of stub 26 is equal to the characteristic admittance of the transmission line which stub 26 has. Then, matching in the output side can be taken by changing the characteristic admittance by changing the line width of stub 26. Meanwhile, the 1/8 wave length line for the fundamental wave becomes 1/4 wave length for the second higher harmonic, and the susceptance which stub 26 has is infinite. Consequently, stub 26 operates as a removal filter for the second higher harmonic. A 1/12 wave length stub is used for the third higher harmonic. Further, this unit is made into a MIC, and plural stubs are provided, so that it becomes small-size and can be operated efficiently.

Patent
21 Jan 1980
TL;DR: In this article, an antenna coupler samples the power transferred between the transmitter and the load, and at two equal distance points from the load connects a tuning stub to the transmission lines that ensures matched impedance conditions.
Abstract: An antenna coupler samples the power transferred between the transmitter and the load, and at two equal distance points from the load. The coupler, based upon the value of the samples, connects a tuning stub to the transmission lines that ensures matched impedance conditions between the transmitter and the load.

Journal ArticleDOI
TL;DR: In this article, optoelectronic switching in a pulseforming microstrip line was demonstrated, which utilizes the energy in a laser pulse for triggering, and pulses 1 ns in width and 1 2 V in amplitude were produced using a 10ns dye laser pulse of 1 kW amplitude.
Abstract: We have demonstrated optoelectronic switching in a pulse‐forming microstrip line, which utilizes the energy in a laser pulse for triggering. Electrical pulses 1 ns in width and of 1–2 V in amplitude were produced using a 10‐ns dye laser pulse of 1‐kW amplitude. The possibilities of further pulse shortening appear very promising.

Patent
09 Dec 1980
TL;DR: A power brush apparatus for cleaning airplanes or the like is described in this paper, which includes an elongate hollow handle with a drive member coaxially mounted and journaled within the hollow handle and which drive member is connected at one end to a drive motor in a driving connection and at the opposite end to the stub shaft arranged in a housing at an angle of about 45° with respect to the longitudinal length of the handle.
Abstract: A power brush apparatus for use in cleaning airplanes or the like which includes an elongate hollow handle with a drive member coaxially mounted and journaled within the hollow handle and which drive member is connected at one end to a drive motor in a driving connection and at the opposite end to a stub shaft arranged in a housing at an angle of about 45° with respect to the longitudinal length of the handle and a brush of the rotatable type is secured for rotation to the terminal end of the stub shaft

Patent
27 Mar 1980
TL;DR: In this article, the U-bend fixture is used to secure a tubular handle end between brackets formed as U-shaped tubes or rods, which may be the side posts of a pushcart.
Abstract: The fixture secures a tubular handle end (6) between brackets formed as U-shaped tubes (3) or rods, which may be the side posts of a pushcart. Housing parts (1b, c) hold the curved end of the U-bend. The complementary parts have a concave profile (2b, c) corresponding with the U-tube (3), whilst one part (1b) has a projection (5b) inserted into the handle end (6) and expandable into this. The projection is longitudinally slotted and expands by fitting a tapered screw (8b) which also secures the parts together.

Patent
Kuhn Friedrich1
09 Oct 1980
TL;DR: The lateral stretch roller assembly as discussed by the authors consists of a number of rollers, arranged side by side at angles relative to one another, carried at both ends by supports arranged between each pair of adjacent rollers via swivel bearings.
Abstract: The lateral-stretch roller assembly is for preventing folds in a continuously moving length of wide paper or similar material or to laterally deflect a number of narrower strips after passing cutters. It comprises a number of rollers, arranged side by side at angles relative to one another. The rollers are carried at both ends by supports arranged between each pair of adjacent rollers via swivel bearings which allow their angular displacement. The bearings may be arranged in the ends of the rollers and run on stub shafts fixed to both sides of each support.

Patent
Antonio Scudellari1
31 Oct 1980
TL;DR: In this article, the authors introduce a minimum redundancy into a microstrip stub for microwave circuits allowing reversibility of adjustment, always operating in the same manner, that is by only removing or by only adding conductive material.
Abstract: Introduction of a minimum redundancy into a microstrip stub for microwave circuits allowing reversibility of adjustment, always operating in the same manner, that is by only removing or by only adding conductive material.

Patent
23 Sep 1980
TL;DR: In this article, a microwave frequency divider operating in 8-16 GHZ range is presented, where the input signal is supplied to the resonant circuit by a pair of microstrip lines functioning as a two stage quarter wave transformer.
Abstract: A microwave frequency divider operable in 8-16 GHZ range. A circuit resonant at a subharmonic frequency is formed by a pair of input microstrip transmission lines coupled to a pair of output microstrip transmission lines. Each input line is terminated by a varactor diode. The input signal is supplied to the resonant circuit by a pair of microstrip lines functioning as a two stage quarter wave transformer. A metal plate positioned over the resonant circuit and closely spaced from it functions to extend the upper end of the frequency range. A bias supply line for the diodes has a portion passing through a resistive foam block to remove spurious signals. A movable stub is positioned along the bias supply line to extend the lower end of the frequency range.

Patent
05 May 1980
TL;DR: In this paper, the resonator is formed with a primary line which is slightly less than a ltiple of a half wavelength long, a tee, and a matching stub, and the primary line and the stub are adjustable to make the total length a multiple of one half wavelength.
Abstract: The resonator is formed with a primary line which is slightly less than a ltiple of a half wavelength long, a tee, and a matching stub. The primary line and the stub are adjustable to make the total length a multiple of one half wavelength. A mechanical link can be connected across the two adjustable lengths so as to maintain a total length of a multiple integral of one half wavelength.

Patent
11 Apr 1980
TL;DR: In this paper, the length of the interconnections between inner conductors and shields of certain ports and the stub, and the lengths of the port and stub lines are defined such that power input to a first port divides equally and in phase between two other ports with matched impedances and no power is at present at the fourth port.
Abstract: Coaxial, impedance-matched, four-port 180° hybrid junctions for multioctave bandwidth operation include a gap in the outer shields of a port and a stub line at their interface for forming a uniform electric field within the gap. This gap and the interconnections between inner conductors and shields of certain ports and the stub, and the lengths of the port and stub lines are such that power input to a first port divides equally and in phase between two other ports with matched impedances and no power is at present at the fourth port. Similarly power fed into the fourth port divides equally, but 180° out of phase, between the two other ports with matched impedances and no power is present at the first port.

Patent
10 Jan 1980
TL;DR: An intrinsically safe device for measuring methane conc. in gas extraction and gathering pipes, which enables direct delay-free continuous measurement and is simple to construct, was presented in this article, where a conventional measurement chamber was connected to an evaluation unit via an electrical measurement conductor.
Abstract: An intrinsically safe device for measuring methane conc. in gas extraction and gathering pipes, e.g. in mining applications, enables direct delay-free continuous measurement and is simple to construct. A conventional measurement chamber (1) is connected to an evaluation unit via an electrical measurement conductor (16). It is also connected via a gas tight screw connector to a cylindrical stub pipe (6) projecting into the gas pipe (4) into which it is screwed. The stub pipe is sealed at its lower end, has peripheral borings (7) near the end which incline upwards, and contains a baffle (8).

Patent
29 Sep 1980
TL;DR: In this paper, a simple but effective filter attenuating one or more frequencies other than the fundamental frequency of a magnetron is provided in the magnetron, which consists of stubs each of which extends along one side of an output probe connected to an anode vane.
Abstract: A simple but effective filter attenuating one or more frequencies other than the fundamental frequency of a magnetron is provided in the magnetron. The filter comprises one or more stubs each of which extends along one side of an output probe connected to an anode vane of the magnetron. Each stub forms a slot which has an effective electrical length of a quarter wavelength at the frequency to be attenuated by the filter. The probe may be a metal strip and the stub, may be a lug formed by cutting in the strip a mainly longitudinal slot which opens into a side edge of the strip.

Patent
06 Feb 1980
TL;DR: An unsheathed grease-filled cable stub has the grease removed from around the insulated wires by subjecting the cable stub to radiant heat over the length of the stub and over a major portion of its circumference while the stub is supported on a flexible open mesh of material that overlies a trough.
Abstract: An unsheathed grease-filled cable stub has the grease removed from around the insulated wires by subjecting the cable stub to radiant heat over the length of the stub and over a major portion of its circumference while the stub is supported on a flexible open mesh of material that overlies a trough. The heated grease melts and flows downwardly for collection into the trough, the grease also flowing through the supporting mesh. The heating temperature of the cable stub is kept low enough to prevent damage to the insulation of the wires.

Journal Article
TL;DR: In this paper, a discussion and comparison of three analysis models for non-prismatic beam programs is presented, including the Vierendeel Truss Model, the simplist of the three, and the Finite Element Model, which is comprised of two-dimensional quadrilateral elements.
Abstract: This paper presents discussion and comparison of three analysis models. The Non-Prismatic Beam Model, the simplist of the three, uses the method of numerical integration for analysis of the stub-girder system as a variable cross section beam. In the numerical procedure, distributed and concentrated external loads are replaced by equivalent concentrated loads spaced equally along the beam at specified pivot points. The Vierendeel Truss Model, which lends itself especially well to the stub-girder system due to its structural nature, analyzes the system by the stiffness method for plane frames. The Finite Element Model is comprised of two-dimensional quadrilateral elements. In comparing the three models, the non-prismatic beam program provides consistently unconservative results when compared to the more accurate Viernendeel Truss Program and Finite Element Program; however, the simplicity of the program and its capabilities for use as a design tool make the non- prismatic beam program a desirable resource. Also included in this paper is a discussion of three parametic studies- stub-girder stiffness ratio, stub-girder length ratio, and stub length ratio, and of design procedure.

Patent
12 Jun 1980
TL;DR: In this article, a coiled section of a plastic sheathed stub cable is placed on a support, which is orbited about a longitudinal axis of a straight section of the stub cable.
Abstract: A coiled section (16) of a plastic sheathed stub cable (10) is placed on a support (43) which is orbited about a longitudinal axis of a straight section (13) of the stub cable. The straight section of cable is positioned coaxially within an aperture formed in a casing part (12) which is mounted in a rotating nest (16). The juncture (70) between the apertured casing and the cable sheath is heated (81), whereafter a bead (91) of bonding material is extruded around the juncture. A molding die (106) is moved into the extruded bead to force portions of the bead into the juncture to form a homogeneous weld with the cable sheath and casing parts while uniformly shaping the remaining portions.


01 Jun 1980
TL;DR: The capability of a marine mammal transmitter to provide data to a satellite receiver to calculate accurate position information was demonstrated using the NIMBUS random access measurement system (RAMS), but emphasis is being shifted to TIROS which has a similar acquisition system but will require modifications to the transmitter package.
Abstract: This TM series is used for documentation and timely communication of preliminary results, interim reports, or similar special purpose information. Although the memos_ are not subject to complete formal review^ еаг^сЕрг^стглл control, or detailed editing, they are ж Bound professional work. One or more conditions of the original document may affect the quality of the image, such as: Discolored pages Faded or light ink Binding intrudes into the text This has been a cooperative project between the NOAA Central Library and the Climate SUMMARY The capability of a marine mammal transmitter to provide data to a satellite receiver to calculate accurate position information was demonstrated using the NIMBUS random access measurement system (RAMS). However, NIMBUS is nearing the end of its design life, and emphasis is being shifted to TIROS which has a similar acquisition system but will require modifications to the transmitter package. The NIMBUS sensor requires 980 m sec to complete an up-link, while the TIROS system will require only 360 m sec, which should improve system performance because of the uncertain dolphin breathing cycle. The TIROS-N quarterwave stub antenna communicated accurate position locations during low power level operations based on data processed by the Local User's Terminal (LUT) and Service ARGOS. This style of antenna is essential for use with a small, portable package, and is ideally suited for use on the marine mammal transmitter package. The antenna gain and radiation pattern (3.5 dBi gain from approximately 30° above the horizontal plane) and vertical polarization enhance the applicability. However, for marine mammal transmitter applications, a spring at the base of the antenna is required to provide flexibility and protection to the animal, and the antenna must serve as a seawater sensor requiring it to be insulated from the seawater environment except at the sensory location. These problems appear to have been solved for the NIMBUS system, and the TIROS system will be designed accordingly.

Journal ArticleDOI
TL;DR: A simple method to transfer and mount the anterior region of worms upright on the standard flat specimen stub, which minimizes the tilting operation required to obtain a proper en face view.
Abstract: Following conventional methods, one usually encounters great technical difficulty in mounting, orientating, and aligning microscopic-size nematodes for en face study using the scanning electron microscope (SEM). Since these specimens are too small to be handled even with extra fine forceps and inevitably become brittle after dehydration, it is a frustrating experience to attempt to transfer and mount the anterior region of worms upright on the standard flat specimen stub. The present report describes a simple method which should alleviate the above problems. The technique involves mainly the use of a special aluminum stub (Figs. 1 and 2). Basically this is a circular stub (13 mm in diameter) with a pyramid-like structure 4 mm high on top. It has two slopes (10 mm in length) inclining 45 ~ to the horizontal. Mounting specimens at such an angle minimizes the tilting operation required to obtain a proper en face view. The stub was molded from an aluminum rod by lathing. After dehydration in absolute alcohol, the specimens are transferred under a microscope, using a hair or pipette, into a bag made of nybolt (Swiss Bolting Cloth Co.) with 5-20 gm mesh size. The bag is made by melting the edges of a nybolt cloth with a hot needle. Air bubbles trapped in the bag are removed by vacuum suction. The specimens within the bag are then critical point dried either in freon 13 or CO2. The bag is then cut and the specimens are emptied onto a petri dish. A small piece of one sided adhesive tape, held by a pair of forceps, is applied under the microscope to the posterior region of worm and the tape is then stuck onto the slanting sides of the stub (with double-faced adhesive tapes) held in a holder. The anterior end of worm protrudes above the " p e a k " of the stub. By using this method, one can quickly mount many specimens on both slopes and number them accordingly. Since the specimens are actually aligned in a row and in a similar direction, they can be scanned systematically with little effort in searching and tilting. The sloping sides provide a firm support for the worm body and thus eliminate worm movements during scanning. Be-

Patent
15 Oct 1980
TL;DR: In this article, an optical transceiver with a light source coupled to a light detector coupled to the termination of an optical fiber is presented. But the detector is disposed adjacent to the low index region of the fibre stub and is provided with an aperture in register with the core.
Abstract: Simultaneous bidirectional transmission of light signals via an optical fibre termination along a fibre coupled to the termination is achieved. The method includes directing outgoing signals into the fibre via a first region of the termination and receiving incoming signals from the fibre via a second region of the termination. There is an optical transceiver device, including an optical fibre stub, whereby the device may be coupled to an optical fibre. The device has a relatively high refractive index core and a relatively low refractive index region surrounding the core, a light source coupled to the core, and a light detector coupled to the low index region. The detector is disposed adjacent the low index region of the fibre stub and is provided with an aperture in register with the core. The aperture provides a path for light signals directed from the source through the core.