LOW NOISE BLOCK (LNB) MOUNTING SYSTEM

Abstract: A mounting cradle (16) for coupling a low noise block (LNB) (12) to a boom arm (14) of a satellite dish antenna (10) is described. The mounting cradle (16) releasably engages the LNB (12) and allows the LNB (12) to rotate around the axis (28) of a waveguide (30) wihtin the LNB (12). A projection (54) on the surface (52) of the LNB (12) engages with one of a series of slots (26a-e) on the cradle (16) which are radially spaced at predetermined angular positions. The projection (54) is located wihtin a desired slot (26) and then secured in place. The mounting cradle (16) ensures that a probe located inside the waveguide (30) wihtin the LNB (12) can be aligned at a predetermined angle with respect to the cradle (16) and hence the boom arm (14) and dish antenna (10) to optimise reception of signals from a particular satellite.

Description: OW NOISE BLOCK (LNB) MOUNTING SYSTEM The present invention relates to satellite communication apparatus and particularly to a system for coupling a low noise block (LNB) to a boom arm of a dish antenna . The front end of a satellite receiver system includes a parabolic circular satellite dish, a boom arm, a mounting bracket and a LNB. An LNB is mounted on one end of the boom arm by a bracket, the other end of the boom arm being secured near the edge of the dish. The LNB includes a waveguide horn to receive signals from the dish. The horn is attached to a waveguide into which one or more probes are disposed for coupling broadcast signals from the waveguide to a circuit board. Such an arrangement is shown in the applicant ' s previous application, International Publication WO 92/22938. The boom arm positions the LNB waveguide horn at the focal point of the dish. In order to optimise reception of broadcast signals for a system in which the signals are linearly polarised, the LNB probes must be aligned with polarisation of the signals from the satellite. (The satellite skew angle) . To achieve this, the most common LNB ' s have a scale printed or cast onto the LNB horn, the scale being in degrees with the zero (0°) degrees mark representing the orientation of the waveguide probes. Each satellite has a specific "footprint", i.e. an area over which its broadcast can be detected. For geostationary satellites transmitting linearly polarised signals, the received polarisation orientation varies with the geographical location of the received site. To compensate for this, the LNB is rotated relative to the bracket on installation by a predetermined amount to the vertical, depending on the geostationary position of the satellite, the location of the received site and transmit offset angle of the satellite. For example, in the case of the Astra 2 series of satellites, the LNB is rotated between 5 and 21 degrees to the vertical depending on the exact location of the receiver site in the UK and Ireland, although -13° to the vertical is used as a nominal adjustment. Once the LNB is positioned within the bracket, it is then secured by conventional means, such as a screw thread. With the above arrangement rotational positioning of the LNB within the bracket is done by eye. An error in rotational angle can result in a loss of signal and also a reduction in cross-polar isolation. Accurate positioning of the waveguide probes with respect to the input satellite signals is crucial to the optimum performance of the receiving system. The bracket is normally a two-part assembly fixed together with 2 or 3 screws which can sometimes create difficulties in assembly. An object of the present invention is to provide an improved LNB mounting system which obviates or mitigates at least one of the aforementioned disadvantages . This is achieved by providing, between the LNB and the LNB mounting bracket, a plurality of predetermined discrete positions corresponding to predetermined angular rotations whereby the LNB can be rotated to engage with one of said positions to achieve a particular angular offset for optimising the reception of satellite signals. In a preferred arrangement the plurality of predetermined discrete positions are located in the LNB mounting bracket and positions engaging means in the form of an upstanding fin or projection is located on the LNB. In an alternative arrangement the discrete positions are disposed on the LNB and the fin is disposed on the bracket . According to a first aspect of the present invention there is provided a mounting cradle for supporting a LNB for use with a dish antenna, the cradle including cradle locating means for permitting, in use, the LNB to be disposed in a predetermined rotational alignment with respect to the cradle. Advantageously, the cradle locating means comprises at least two slots, each slot being disposed substantially parallel to a longitudinal axis of the cradle. Preferably, the at least two slots are arranged on an arc of a circle, the centre of which is coaxial with the axis of the waveguide in the LNB . In a preferred embodiment there are provided five slots substantially equally spaced apart on said arc. Where a plurality of slots are provided adjacent slots may be substantially equally spaced around the arc by approximately 4°. Preferably the cradle has fastening means for connecting the cradle to a boom arm of the dish antenna. In an alternative arrangement the cradle is formed integrally with the boom arm. The cradle may be fabricated from polypropylene or any other suitable material, for example a polymer. The cradle may include connection means for connecting the cradle to the LNB. The connection means may comprise an aperture formed through the cradle which, in use, may receive a threaded bolt therethrough which is received within a further aperture formed in the LNB. The cradle may provide a surface for receiving corresponding surface of the LNB. Conveniently the surface is cylindrical . The surface may include a drainage hole or channel which is longitudinally disposed thereupon. The cradle may further include at least one drainage aperture which communicates with the cylindrical surface. Where a drainage channel is provided the drainage channel may drain into the drainage aperture. The cradle may also include releasable engaging means for releasably engaging the LNB. The releasable engaging means may comprise at least one pair of resiliently deformable lugs, each lug of a pair being disposed apart in substantially opposing relationship to define a space for receiving the LNB. According to a second aspect of the present invention, there is provided a low noise block (LNB) for use with a dish antenna which LNB, in use, is supported by a mounting cradle, the LNB including LNB locating means for locating the LNB in a predetermined rotational alignment with respect to the cradle. Preferably the LNB locating means comprises a projection upstanding from a surface of the LNB. The LNB may include a horn and the projection is located on an outer surface of the horn. The LNB includes a housing with a waveguide having one or more probes located therein. The probe may be of the type disclosed in International Patent Application WO 92/22938 by the same applicant, the content of which is incorporated herein by reference. The horn may be of an elliptical type, for example as disclosed in U.S. Patent No. 5,552,797. The LNB may include connection means for connecting the LNB to the cradle . The connection means includes an aperture formed on the LNB and adapted to receive a threaded bolt . The projection may be located at an offset angle with respect to the probe. The offset angle depends on the three factors described above and in the UK the offset angle is nominally set to -13.5 degrees (Astra 2 series) , although the exact offset will depend on the geographical location of the receiver site. According to a third aspect of the present invention there is provided a dish antenna receiver system comprising a dish antenna, an antenna boom arm, a cradle and a LNB, the cradle and the LNB being coupled to said boom arm for locating the LNB and the cradle relative to the dish antenna, said cradle and LNB including position adjustment means for enabling the LNB and the cradle to be disposed in a predetermined rotational alignment with respect to one another. This is achieved by creating a plurality of predetermined angular offsets in said cradle for locating a projection on an outer surface of the LNB for engaging with one of said offsets. The dish antenna can be an elliptical type or a circular type. Conveniently, the dish has dimensions 520mm by 390mm. The cradle and receiver are positively located with respect to each other by the projection on the LNB being disposed in a slot on the cradle. According to a fourth aspect of the present invention there is provided a method of aligning a LNB monitor to a satellite dish antenna to optimise the signal reception for a particular satellite, said method comprising the steps of, locating the LNB in a LNB mounting cradle, providing a plurality of discrete predetermined offset positions between the LNB and the cradle, and rotating the LNB relative to the cradle to one of said predetermined offset positions. According to a fifth aspect of the present invention there is provided a mounting cradle for supporting a LNB when mounted to a dish antenna, the cradle including a LNB engaging surface, said surface having a plurality of spaced slots, each of said slots being adapted to receive a projection on the LNB for locating the LNB at a particular offset angle from the vertical to optimise satellite signals at the site of said dish antenna. The cradle may include resilient means for releasably engaging the LNB. Advantageously, in use, the surface of the receiver is received in close-fitting contact with the LNB engaging surface of the cradle. According to a sixth aspect of the present invention there is provided a cover for a mounting cradle and LNB, the cover including means for attaching to LNB and cradle . The cover may be fabricated from polypropylene. The cover may be in two or more sections including means for attaching the parts together. The means for attachment is provided by recessed edges on the sections for snap-fitting the sections together. Advantageously the cover may entirely enclose the LNB and/or the cradle. These and other aspects of the present invention will become apparent from the following description when taken in combination with the accompanying drawings in which: Fig. 1 is a diagrammatic representation of a dish antenna with a boom arm with mounting cradle, LNB and cover in accordance with an embodiment of the present invention; Fig. 2 is a diagrammatic representation of a mounting cradle in accordance with a preferred embodiment of the present invention; Fig. 3 depicts part of a cross-sectional view through the horn of Fig. 1 taken longitudinally through the centre of the horn; Fig. 4 is an enlarged diagrammatic representation of part of the underside of the mounting cradle when engaged with the horn showing with the fin located in the central slot, and Fig. 5 depicts part of a cross-sectional view through the LNB and mounting cradle with the fin located in an offset slot . Reference is made to Fig. 1 of the drawings which depicts a parabolic satellite receiving dish antenna, generally indicated by reference numeral 10, having a low noise block (LNB) receiver, generally indicated by reference numeral 12, mounted thereto by means of a boom arm 14 and mounting bracket hereinafter referred to as a cradle 16 . Reference is now made to Fig. 2 of the drawings which depicts the mounting cradle 16 in accordance with a preferred embodiment of the present invention. The mounting cradle 16 has four main parts; a pair of resilient lugs 18 for securing the LNB 12 to the cradle ,- a box- like end 20 for securing the cradle 16 in boom arm 14; a cylindrical surface 22 for supporting the LNB 12 when located in the cradle 16, and LNB position setting means 24 provided by a series of five slots 26a-e for engaging with a projection on the surface of the LNB 12 so as to ensure that the LNB 12 is offset by a predetermined angular amount to align the probes within the LNB with the polarisation of signals from the satellite. Referring also to Figs. 3, 4 and 5 the five slots 26a-e are disposed parallel to the longitudinal axis 28 of the cradle 16. The slots 26a-e are separated circumferentially, each on a radius whose centre is nominally the axis 28 of the waveguide 30 (Fig. 3) located within the LNB 12 when the LNB 12 is mounted to the cradle. As best seen in Fig. 5, the locating slots 26a- e are defined by ribs 32 to produce a raised apex 33 on each side of the slots 26a-e. There are five slots on radius of 27.5mm, each slot is radially separated from its adjacent slot (s) by 4°. Reference is now made to Fig. 4 of the drawings, which shows the locating slots 26a-e located adjacent a slot 34 and securing screw 35 for coupling the cradle 16 to the LNB 12 as will be described. An aperture is formed in the cradle 16 by a slot 34 which is wide enough to accept the self-retaining securing screw. When the securing screw 35 is slackened it is retained in the slot but allows the LNB 12 to be rotated relative to the cradle 16 over all slot positions 26a-e. A recess 37, best seen in Fig 2, is located above the slot 34 and is dimensioned to receive a securing screw housing 38 (Fig. 3) located on the LNB horn 40. Connection of the cradle 16 to the boom arm 14 is achieved by coupling a box-like end 30 into a steel tube 42 of similar cross-sectional on the end of the boom arm 14. The cradle is secured by means of a screw 44 locating within slot 46. One end of the cradle has the cylindrical surface 22 which matches the outer surface of the LNB waveguide 30. Drainage is provided on the surface 22 by a drainage hole 48, located at the middle of the curved surface. Resilient lugs 18 are located on either side of the surface 22 and are also shaped to match the outer surface of the LNB waveguide 30 of the LNB 16. Referring back to Fig. 2, corner sections radially adjacent to locating slots 26a-e are removed to leave recessed surfaces 50 to allow adequate clearance to the horn outer surface 52 and allow the LNB 12 to be fitted to the cradle 16 as shown. A fin 54 is upstanding from the horn surface 52 and may be radially offset with respect to the position of a probe within the waveguide 30. The offset, as described above, depends on 3 factors and in this case the offset can be from +8 degrees to -8 degrees. As shown in Figs. 4 and 5, the fin 54 has a width which matches the width of each of locating slots 26a-e. The screw housing 38 located behind the fin 54 has a square section which fits into the recess 37 on the mounting cradle 16. The housing 38 receives the securing screw 44 shown in Fig 1. Reference is again made to Figs. 4 and 5 of the drawings which depict in detail the means for locating and securing the LNB 12 to the cradle 16. A raised scale 58 is located adjacent to the locating slots 26a-e; the scale indicates the angular offsets provided by each of the locating slots 26a-e. The central slot 26a is labelled 0° degrees with the accompanying slots 26b, c,d and e labelled +4, +8, -4 and -8 degrees respectively. In a pre- installation phase the LNB 12 is located in the cradle 16 by placing the waveguide 30 onto the surface 46 with the resilient retaining lugs 18 engaging the waveguide 30. The fin 54 is located in the central slot 26a and screw housing 38 is located in recess 37 and securing screw 35 is then tightened. The cradle 16 and LNB 12 are then mounted on the boom arm 14 by fitting the box-like end 20 into the tube 42 and securing the screw 44 in the slot 46. In use, an installer optimises the signal by slackening the screw 35, and rotating the LNB 12 relative to the cradle 16 to move the fin 54 across the slots 26a- e to the desired slot location and, at the desired slot, retightening the screw 34 to secure fin 54 into a slot, for example slot 26e, to give an angular offset of -8°. A protective polypropylene cover 60 (Fig. 1) is located over the LNB 12 and part of the mounting cradle 16. The cover 60 is shaped to match the outer surfaces of the assembled LNB 12 and mounting cradle 16. For ease of mounting, the cover 60 is fabricated in two separate sections 60a, 60b with each section having opposing recessed edges to form a snap-fit. Section 60b has a cut-out 64 to allow the cradle 16 to be mounted on the boom arm 14 and, additionally, to facilitate realignment of the LNB 12 with respect to the cradle 16 when installed on the boom arm 14. Various modifications may be made to the embodiment hereinbefore described without departing from the scope of the invention. For example, the number and spacing of the slots can be varied to suitable particular satellite/receiver systems and spaced notches could be located on the horn or waveguide to engage with a single slot or fin on the cradle. The invention may be applied to many different types of LNB - bracket/cradle configurations and may be used with a variety of antenna systems not just those using circular or elliptical dish antennas . It will be appreciated that the principal advantage of the present invention is that the probe located inside the waveguide section within the receiver can be aligned at a predetermined angle with respect to the cradle and hence the boom arm and, dish antenna to optimise reception of signals from the particular satellite broadcasting the linearly polarised signals. This allows both rapid and accurate installation of the receiver, facilitating use by a semi-skilled person. A further advantage is that the 'notch' engagement provides tactile feedback to an installer to provide a more accurate indication of the degree of rotation which has been made. Yet another advantage lies in the ease of assembly and installation compared to the prior art : adjustment is simply achieved by slackening a retained screw, rotating the LNB through a number of notches or slides to the desired position and then retightening the screw.

Claims: CLAIMS 1. A mounting cradle for supporting a low noise block (LNB) for use with a dish antenna, the cradle including cradle locating means for permitting, in use, the LNB to be disposed in a predetermined rotational alignment with respect to the cradle. 2. A mounting cradle as claimed in claim 1 wherein the cradle locating means comprises at least two slots. 3. A mounting cradle as claimed in claim 2 wherein the at least two slots are disposed substantially parallel to a longitudinal axis of the cradle. 4. A mounting cradle as claimed in claim 2 or claim 3 wherein the at least two slots are arranged on an arc of a circle, the centre of which is coaxial with the axis of a waveguide in the LNB. 5. A mounting cradle as claimed in any one of claim 4 or claim 5 wherein there are provided five slots substantially equally spaced apart on said arc. 6. A mounting cradle as claimed in claim 4 or claim 5 wherein adjacent slots are substantially equally spaced around the arc by approximately 4°. 7. A mounting cradle as claimed in any preceding claim wherein the cradle includes fastening means for connecting the cradle to a boom arm of the dish antenna. 8. A mounting cradle as claimed in any one of claims 1 to 6 wherein the cradle is formed integrally with a boom arm. 9. A mounting cradle as claimed in any preceding claim wherein the cradle is fabricated from a polymer. 10. A mounting cradle as claimed in any preceding claim wherein the cradle includes connection means for connecting the cradle to the LNB. 11. A mounting cradle as claimed in claim 10 wherein the connection means comprises an aperture formed through the cradle which, in use, receives a threaded bolt therethrough which is received within a further aperture formed in the LNB . 12. A mounting cradle as claimed in any preceding claim wherein the cradle includes a surface for receiving a corresponding surface of the LNB . 13. A mounting cradle as claimed in claim 12 wherein the surface is cylindrical. 14. A mounting cradle as claimed in claim 12 or claim 13 wherein the surface includes a drainage hole or channel which is longitudinally disposed thereupon. 15. A mounting cradle as claimed in claim 13 or claim 14 wherein the cradle includes at least one drainage aperture which communicates with the cylindrical surface. 16. A mounting cradle as claimed in claim 15 wherein the drainage channel drains into the drainage aperture. 17. A mounting cradle as claimed in any preceding claim wherein the cradle includes releasable engaging means for releasably engaging the LNB. 18. A mounting cradle as claimed in claim 17 wherein the releasable engaging means comprises at least one pair of resiliently deformable lugs. 19. A mounting cradle as claimed in claim 18 wherein each lug of a pair is disposed apart in substantially opposing relationship to define a space for receiving the LNB. 20. A low noise block (LNB) for use with a dish antenna which LNB, in use, is supported by a mounting cradle, the LNB including LNB locating means for locating the LNB in a predetermined rotational alignment with respect to the cradle . 21. A LNB as claimed in claim 20 wherein the LNB locating means comprises a projection upstanding from a surface of the LNB . 22. A LNB as claimed in claim 20 or claim 21 wherein the LNB includes a horn and the projection is located on an outer surface of the horn. 23. A LNB as claimed in any one of claims 20 to 22 wherein the LNB includes a housing with a waveguide having one or more probes located therein. 24. A LNB as claimed in claim 23 wherein the housing includes apparatus for receiving at least two signals which are orthogonally polarised, said apparatus comprising a waveguide into which said at least two orthogonally polarised signals are received for transmission therealong, said waveguide having; a first probe extending from a wall of the waveguide into the interior of the waveguide, said first probe being adapted to receive said orthogonal signal travelling in the same longitudinal plane thereof, reflector means extending from the wall of the waveguide, said reflector means located downstream of said first probe and lying in said longitudinal plane for reflecting signals in said first orthogonal plane back to said first probe means and allowing said signal in said second orthogonal plane to pass along the waveguide, second probe means located downstream of said first reflector means and extending from said wall of said housing into the interior of said waveguide and lying in said longitudinal plane, reflecting and rotating means located downstream of said second probe means for receiving, rotating and reflecting said second orthogonally polarised signal back along said waveguide such that said rotated and reflected signal is received by said second probe means, the first and second probes having respective first and second outputs located on the outside of the waveguide, the first and second outputs lying in substantially the same longitudinal plane. 25. A LNB as claimed in any one of claims 22 to 24 wherein the horn is elliptical. 26. A LNB as claimed in any one of claims 20 to 25 wherein the LNB includes connection means for connecting the LNB to the cradle. 27. A LNB as claimed in claim 26 wherein the connection means includes an aperture formed on the LNB and adapted to receive a threaded bolt. 28. A LNB as claimed in any one of claims 21 to 27 wherein the projection is located at an offset angle with respect to the probe. 29. A LNB as claimed in claim 28 wherein the offset angle is nominally set to -13.5 degrees. 30. A dish antenna receiver system comprising a dish antenna, an antenna boom arm, a cradle and a LNB, the cradle and the LNB being coupled to said boom arm for locating the LNB and the cradle relative to the dish antenna, said cradle and LNB including position adjustment means for enabling the LNB and the cradle to be disposed in a predetermined rotational alignment with respect to one another, said cradle including a plurality of predetermined angular offsets for locating a projection on an outer surface of the LNB for engaging with one of said offsets. 31. A dish antenna receiver system as claimed in claim 30 wherein the dish antenna is an elliptical dish antenna. 32. A dish antenna receiver system as claimed in claim 30 wherein the dish antenna is a circular dish antenna. 33. A dish antenna receiver system as claimed in claim 30 or claim 31 wherein the dish has dimensions 520mm by 390mm. 34. A dish antenna receiver system as claimed in any one of claims 30 to 33 wherein the cradle and the LNB are positively located with respect to reach other by the projection on the LNB being disposed in a slot on the cradle. 35. A method of aligning a LNB to a satellite dish antenna to optimise the signal reception for a particular satellite, said method comprising the steps of, locating the LNB in a LNB mounting cradle, providing a plurality of discrete predetermined offset positions between the LNB and the cradle, and rotating the LNB relative to the cradle to one of said predetermined offset positions. 36. A mounting cradle for supporting a LNB when mounted to a dish antenna, the cradle including a LNB engaging surface, said surface having a plurality of spaced slots, each of said slots being adapted to receive a projection on the LNB for locating the LNB at a particular offset angle from the vertical to optimise satellite signals at the site of said dish antenna. 37. A mounting cradle as claimed in claim 36 wherein the cradle includes resilient means for releasably engaging the LNB. 38. A mounting cradle as claimed in claim 36 or claim 37 wherein, when supported, a surface of the LNB is in close-fitting contact with the LNB engaging surface of the cradle. 39. A cover for a mounting cradle and a LNB, the cover including means for attaching to the LNB and the cradle. 40. A cover as claimed in claim 39 wherein the cover is in two or more sections including means for attaching the sections together. 42. A cover as claimed in claim 41 wherein the means for attachment has recessed edges on the sections for snap- fitting the sections together. 43. A cover as claimed in any one of claims 39 to 42 wherein the cover entirely encloses the LNB and/or the cradle .

Inventors: GRICE DEREK ARTHUR HENRY, WILSON SIMON PAUL, GRICE, DEREK, ARTHUR, HENRY, WILSON, SIMON, PAUL
Applicants: CAMBRIDGE IND LTD, GRICE DEREK ARTHUR HENRY, WILSON SIMON PAUL, CAMBRIDGE INDUSTRIES LIMITED, GRICE, DEREK, ARTHUR, HENRY, WILSON, SIMON, PAUL
Application year: 1999
Main classification: H01Q1
IPC codes: H01Q1, H01Q3