GB2368467A

GB2368467A - Satellite signal receiving unit

Info

Publication number: GB2368467A
Application number: GB0026080A
Authority: GB
Inventors: John Arthur Drew
Original assignee: STANFORD COMPONENTS Ltd
Current assignee: STANFORD COMPONENTS Ltd
Priority date: 2000-10-25
Filing date: 2000-10-25
Publication date: 2002-05-01
Anticipated expiration: 2020-10-25
Also published as: GB0026080D0; GB2368467B

Abstract

A satellite signal receiving unit 10, comprises a dish assembly 30 and a mounting assembly. The dish assembly 30 includes an elliptical reflector dish 36 and a projecting support arm 38 for locating an antenna 42 at the focus of the reflector dish 36. The mounting assembly includes mounting members 14, 20 and 26 that are pivotable relative to one another about mutually inclined axes and that serve to mount the dish assembly 30 on a stationary support surface 12 with the axis of the dish 36 set at desired angles of azimuth and elevation. The dish assembly 30 is rotatable relative to the mounting members 26 about an axis 34 parallel to the axis of the dish, so that the angle between the major axis of the reflector 36 and the horizontal is adjustable to enable the reflector 36 to be aligned with the plane of polarisation of the incoming signal, without affecting the setting of the angles of azimuth and elevation. A spirit level 44 is provided to ensure that the major axis of the relector dish is set at an angle corresponding to the plane of polarisation of the incoming signal.

Description

SATELLITE SIGNAL RECEIVING UNIT

Field of the invention The present invention relates to a satellite signal receiving unit and in particular to a satellite signal receiving unit designed for digital television signal reception.

Background of the invention A satellite receiving unit comprises a dish assembly that includes a reflector dish and a support arm that projects forward of the reflector dish to mount an antenna or LNB at the focus of the dish. The dish assembly is mounted on a building by means of a suitable mounting assembly which allows it to be held with its axis pointing at a satellite. The mounting assembly allows the axis of the reflector dish (i. e. its direction of maximum sensitivity) to be pivoted about two orthogonal axes so that it may be pointed in any desired direction. If the azimuth and elevation settings are to be independent of one another, one axis should be generally vertical to allow the azimuth angle (compass bearing) to be set correctly and the second axis should be generally horizontal to allow the elevation angle (the angle between the satellite and the horizon) to be set correctly. For ease of reference, these two axes will be termed herein the azimuth axis and the elevation axis, respectively.

It is known to provide an adjustment within the antenna or LNB to allow it to be rotated about an axis generally parallel to the axis of the dish. This is because the incoming signal is plane polarised and whereas the plane of polarisation is nominally horizontal, it does vary by a few degrees from the horizontal, depending on the geographical location of the receiver. The adjustment provided on the

antenna is intended to compensate for the skew of the polarisation of the incoming signal.

The reflector dishes used in analogue television signal receiving units are generally circular and they are sensitive over a relatively wide range of angles. As a result, slight misalignment of the reflector dish can be tolerated. By contrast, the elliptical reflector dishes used for digital television reception are far less tolerant of misalignment in azimuth or elevation and this problem is made worse if the skew of the plane of polarisation is set incorrectly.

Because of the greater directional sensitivity of digital satellite dishes, and difficulty in setting the skew angle, digital reception has proved unreliable and numerous call-outs to service engineers have been caused by improper alignment of newly installed receiving units.

Object of the invention The present invention therefore seeks to provide a digital satellite signal receiving unit in which the elliptical reflector dish can readily be mounted securely and aligned correctly in terms of azimuth, elevation and skew.

Summary of the invention In accordance with the present invention, there is provided a satellite signal receiving unit, comprising a dish assembly and a mounting assembly, the dish assembly including an elliptical reflector dish and a projecting support arm for locating an antenna at the focus of the reflector dish, and the mounting assembly including mounting members that are pivotable relative to one another about mutually inclined axes and that serve to mount the dish

assembly on a stationary support surface with the axis of the dish set at desired angles of azimuth and elevation, characterised in that the dish assembly is rotatable relative to the mounting members about an axis parallel to the axis of the dish whereby the angle between the major axis of the reflector and the horizontal is adjustable to enable the reflector to be aligned with the plane of polarisation of the incoming signal, without affecting the setting of the angles of azimuth and elevation.

In the prior art receiving units, it was assumed that the wall surface for mounting the satellite dish would lie in a vertical plane. As the axes of rotation of the mounting members are all referenced to this surface, it was then assumed that the major axis of the elliptical reflector would be horizontal and that the skew angle could be set by simply rotating the antenna relative to the dish.

In practice, many of these assumptions prove to be incorrect. On account of minor irregularities in the surface of the wall, the azimuth axis of even a well constructed mounting assembly may end up inclined to the vertical in the vertical plane normal to the wall. Such an error in the attitude of the azimuth axis does not affect the horizontal attitude of the major axis of the dish if pointed perpendicular to the wall, but if the dish is turned to point to the right or left then the error in the azimuth axis would result in the dish being mounted askew (its major axis would not be horizontal). Furthermore, rotating the LNB relative to the elliptical dish to compensate for skew means that the dimension of the reflector in the plane of sensitivity of the LNB is less than the full width of the reflector.

The present invention mitigates these problems in that it provides an adjustment that allows the major axis of the reflector dish to be inclined to the horizontal at the same

angle as the polarisation of the incoming signal without having to assume that the wall is vertical. Furthermore, by setting the major axis of the dish at the same angle to the horizontal as the skew of the plane of polarisation of the satellite signal, the bracket permits the use of an LNB having no skew adjustment and ensures that full use is made of the maximum width of the reflector dish.

It is preferred to provide a spirit level on the dish assembly to ensure that the major axis of the elliptical reflector dish is set at an angle corresponding'to the plane of polarisation of the satellite signal.

It is advantageous to mount the spirit level in a location, such as on the antenna support arm, that remains visible when the dish is in its desired final position.

In one embodiment of the invention, the mounting of the spirit level on the support arm may be adjustable so that the spirit level may be inclined relative to the major axis of the dish by an amount corresponding to the desire skew angle. In this way, it can be ensured that when the spirit level is horizontal, the major axis of the dish will be inclined at the desired skew angle relative to the horizontal.

In an alternative embodiment, a calibration scale may be provided about the axis of rotation of the dish assembly whereby, after the spirit level has been used to find the horizontal setting of the major axis of the dish, it may be rotated using the calibrated scale to the desired skew angle.

Brief description of the drawing The invention will now be described further, by way of example, with reference to the accompanying drawing, which

is a schematic plan view of a satellite receiving unit of the invention.

Detailed description of the preferred embodiment A satellite receiving unit 10 is shown in plan in the drawing mounted on a vertical wall 12. The receiving unit 10 is formed of a mounting assembly, comprising various mounting members that can move relative to one another, and a dish assembly 30. The mounting assembly supports the dish assembly on the wall and holds it in a position in which it points at the satellite.

The mounting members in the illustrated embodiment comprise a wall plate 14 that is fixed to the wall 12 using appropriate fixings, such as expansion bolts 16. Two horizontal flanges (18) project from the plate 14 and capture between them a pivotable arm 20. In common with all the other mounting members of the described preferred embodiment, the arm 20 is made of sheet metal.

The arm 20 is pivotable about two spigots 22 that project from the flanges 18 and it can be locked in any desired position by means of clamping bolts 24. The opposite end of the arm 20 carries a universal joint generally designated 26. The universal joint 26 comprises a first member 26a that defines two forks having pivot axis that are orthogonal to one other. A first of the forks is pivoted on the end of the arm 20 about an axis parallel to the axis of the spigots 22 and can be locked in any desired position by means of clamping bolts 28. The second fork defined by the member 26a is connected to a U-shaped second member 26b which can pivot relative to the member 26a about an axis perpendicular to that of the spigots 22 and clamped in any position by means of a bolt 27. The base or cross-piece of the U-shaped member 26b acts as the surface onto which the dish assembly 30 is mounted.

The dish assembly 30 comprises a backing plate 32 that is mounted on the member 26b by a single bolt 34 such that the entire dish support assembly can rotate about the axis of the bolt 34, the axis of which is perpendicular to both of the pivot axes of the universal joint 26. An elliptical reflector dish 36 is held by small bolts or screws (not shown) on the backing plate 32. A support arm 38, secured to the backing plate 32 by means of a bolt 40, projects forward of the reflector dish 36 to its point of focus. The free end of the support arm 38 carries an antenna B 42 and at its end near the reflector dish 36 the arm 38 carries a spirit level 44.

The universal joint 26 and the pivotable arm 20 provide sufficient degrees of freedom to enable the directional sensitivity pattern or axis of the dish 36 to be pointed in any desired direction. In particular, by rotation about the clamping bolt 28 the dish can be made to point in any desired azimuth direction and by rotation about the axis of the bolt 27 the elevation may be set. The fact that the arm 20 can also pivot about the spigots 22 gives further freedom in the mounting of the dish in that the arm 20 can lie to the right or to the left of the mounting pate and, if desired, the dish may be mounted to look round the corner of a building.

The above description assume that the arm 20 is horizontal and is pivotable about a vertical axis. This however need not be the case as the mounting plate could be secured to a horizontal surface and the arm 20 rotated to extend vertically. When mounted in this manner, rotation about the axis of the bolt 28 would permit the elevation to be set and rotation about of the axis of the bolt 27 would permit the azimuth angle to be set.

It will be clear from the foregoing description that the mounting members 14,20 and 26 can support the dish

assembly 30 on virtually any fixed surface of a building while permitting the axis of the dish to be pointed at the satellite.

The signal received from the satellite is polarised and it is additional necessary to be able to set the reflector dish 36 so that its major axis lies parallel to the direction of polarisation. While the direction of polarisation is generally horizontal, it varies with the geographic location of the receiving unit on account the curvature of the earth. Hitherto such variation or skew of the plane of polarisation of the incoming signal was compensated for by rotating the antenna 42 by a few degrees relative to the major axis of the elliptical reflector dish 36. This however resulted in the antenna 42 not making use of the full available width of the reflector dish 36. In the present invention, the entire dish assembly 30 can be rotated about the axis of the bolt 34 to align the major axis of the dish reflector 36 with the axis of polarisation of the incoming signal without at the same time having any effect on the setting of the angles of azimuth and elevation.

To ensure correct setting of the skew angle, a spirit level 44 is mounted on the support arm 38 so that it rotates with the reflector dish 36 and with the antenna 42. When mounted in the illustrated position at the base of the arm 38, the spirit level 44 can readily be seen by the person installing the receiving unit even after the reflector dish has been mounted in its desired position.

To allow the major axis of the reflector dish 36 to be set at the desired skew angle, it is possible to provide an adjustment on the spirit level so that it lies at an angle to the dish. Alternatively the spirit level may be set parallel to the major axis of the dish 36 and a calibration scale can be provided about the axis of the bolt 34 allowing the dish assembly 30 to be rotated by the desired skew angle after the horizontal position of the dish has been determined.

Claims

1. A satellite signal receiving unit, comprising a dish assembly and a mounting assembly, the dish assembly including an elliptical reflector dish and a projecting support arm for locating an antenna at the focus of the reflector dish, and the mounting assembly including mounting members that are pivotable relative to one another about mutually inclined axes and that serve to mount the dish assembly on a stationary support surface with the axis of the dish set at desired angles of azimuth and elevation, characterised in that the dish assembly is rotatable relative to the mounting members about an axis parallel to the axis of the dish whereby the angle between the major axis of the reflector and the horizontal is adjustable to enable the reflector to be aligned with the plane of polarisation of the incoming signal, without affecting the setting of the angles of azimuth and elevation.

2. A receiving unit as claimed in claim 1, wherein a spirit level is provided on the dish assembly to ensure that the major axis of the elliptical reflector dish is set at an angle corresponding to the plane of polarisation of the satellite signal.

3. A receiving unit as claimed in claim 2, wherein the spirit level is mounted in a location that remains visible when the dish is in situ.

4. A receiving unit as claimed in claim 3, wherein the spirit level is mounted on the antenna support arm.

5. A receiving unit as claimed in any of claims 2 to 4, wherein the spirit level is adjustably mounted relative to the major axis of the reflector dish so that the spirit level may be inclined relative to the major axis of the dish by an amount corresponding to the desire skew angle.

6. A receiving unit constructed substantially as herein described with reference to and as illustrated in the accompanying drawings.

6. A receiving unit as claimed in any of claims 2 to 4, wherein a calibration scale is provided about the axis of rotation of the dish assembly.

7. A receiving unit constructed substantially as herein described with reference to and as illustrated in the accompanying drawings.

Amendments to the claims have been filed as follows

1. A satellite signal receiving unit, comprising a dish assembly and a mounting assembly, the dish assembly including an elliptical reflector dish and a projecting support arm for locating an antenna at the focus of the reflector dish, and the mounting assembly including mounting members that are pivotable relative to one another about mutually inclined axes and that serve to mount the dish assembly on a stationary support surface with the axis of the dish set at desired angles of azimuth and elevation, wherein the dish assembly is rotatable relative to the mounting members about an axis parallel to the axis of the dish whereby the angle between the major axis of the reflector and the horizontal is adjustable to enable the reflector to be aligned with the plane of polarisation of the incoming signal, without affecting the setting of the angles of azimuth and elevation, and wherein a spirit level is provided on the dish assembly to ensure that the major axis of the elliptical reflector dish is set at an angle corresponding to the plane of polarisation of the satellite signal.

2. A receiving unit as claimed in claim 1, wherein the spirit level is mounted in a location that remains visible when the dish is in situ.

3. A receiving unit as claimed in claim 2, wherein the spirit level is mounted on the antenna support arm.

4. A receiving unit as claimed in any of claims 1 to 3, wherein the spirit level is adjustably mounted relative to the major axis of the reflector dish so that the spirit level may be inclined relative to the major axis of the dish by an amount corresponding to the desire skew angle.

5. A receiving unit as claimed in any preceding claim, wherein a calibration scale is provided about the axis of rotation of the dish assembly.