GB2188147A - Aerial alignment - Google Patents

Abstract

A method of aligning aerials and an apparatus for use in such a method is disclosed. The apparatus has a body (41) which may be attached to an aerial, and an arm (42) bearing a target (54, 55) which arm is jointed to the body. The method requires a remote observation point to be selected, and the arm to be arranged with respect to the body so that when the aerial, with the apparatus attached, is correctly aligned, the observer can determine from the target that the arm is pointed directly at him. <IMAGE>

Description

SPECIFICATION Aerial alignment This invention relates to a method of aligning aerials and apparatus suitable for use in such a method. Particularly, but not exclusively the method and apparatus may be used to align aerials consisting of an arrangement having a rod-like receiver/radiator positioned substantially vertically in front of a parallel rod-like reflector.

This type ofaerial is used, for example, atfrequen- cies ofthe order of 900MHz in celiular radiotelephone systems to communicate with mobile transceivers. Six such aerials, each capable of communicating over a 600 sector, may be located on a high building for tower, or mast in orderto provide omni-directional (360 ) coverage over one cell of a cellular network. Clearly the aerials must be oriented correctly not only with respect to each other so that coverage is complete and non-overlapping within a particular cell; but also with respect to the reference direction (usuallygrid North) bywhichthecellsare laid out, in order to prevent gaps occurring between the ceils.

Up to the present time aerials have been aligned using a magnetic compass. Wherethere is enough space on the roof of the building a sighting from, say, ten feet is taken along the line between the radiatingand reflecting-rods using a hand-held compass. A suitable correction to take into account the variation from magnetic North and deviations due to local fields is made, and the entire aerial arrangement rotated accordingly.

Where there is not sufficient space to enable a siting to be taken, a collar is fitted between the radiating and reflecting rods. This collar bears a compass and, again after a suitable adjustment has been taken into account, the entire aerial arrangement is rotated until the desired compass reading is attained.

The accuracy of these methods is limited and depends, among other things, an the distance between compass and aerial. Given the limited space available and the dangerous working conditions accuracy of better than +7 is considered good, and errors of upto ill0arecommonlyfound.

The accuracy of the orientation of the aerials is usually checked by travelling throughoutthe network cell with a mobile transceiver and measuring the transmitted field strength. When areas are located where the field strength fails to reached the required minimum the offending aerials are identified and teams sent to re-orient them. Clearly this proce dure is inefficient.

Two alternative methods of checking the accuracy oftheorientation have also been used. Inthefirst,a rigid arm bearing a vertical rod at its remote end is strapped to the aerial, in order that a remote observer can judge whether the aerial is pointing towards the desired position. In the second, a rigid arm bearing gun-sights is mounted onto the aerial in order that an observer at the aerial can judge whetherthe aerial is aimed at a suitable target. Both those methods suffer from the limitation that they require the geography of the locality to provide an accessible vantage point, in the desired direction of orientation, from which: in the first case, the oberver may seethe aerial; and in the second case, the target may be seen from the aerial.

According to the present invention there is prov idedanapparatusforaligning aerials, comprising a body and an elongate arm rotatably interconnected such thatthe arm may be rotated in the horizontal plane relative to the body; the body bearing fixing meansforattachmentto an aerial, and bearing scale means by which the angular relationship between the body and arm may be measured; the arm bearing parallax effect target means by which its orientation may be determined by a remote observer.

Also according to the present invention there is provided a method of aligning aerials using an apparatus as defined above comprising the steps of: selecting an observation point in the locality of the aerial; determinging the direction of the observation point from the aerial with respect to a reference direction; arranging the arm at an angle relative to the body in accordance with the determination such that, if the body were attached to the aerial, the arm would point in the direction of the observation point when the aerial was correctly aligned with respect to the reference direction; attaching the body to the aerial; adjusting the alignment of the aerial until an observer at the observation point, after consideration of the parallax effect of the target means, signals that the arm of the apparatus is oriented in the direc- tion ofthe observation point.

The invention will now be described byway of example with reference to the accompanying drawings in which: Figure la shows a perspective view of an aerial arrangement having a rod-like receiver/radiatorand parallel reflector; Figure ib shows a plan view of the aerial arrange mentor Figure la; Figure2 shows the arrangement of six aerials on a building providing omni-directional coverage in one cell of a cellular network; Figure3shows a preferred embodimentofappar- atusaccordingtothe present invention; Figure4shows various views of a simplified version ofthe apparatus shown in Figure 3.

The same reference numerals have been used throughout the Figures two indicate corresponding features.

Referring nowtoFigure 1a,there is shown an aerial arrangement having a receiving/radiating element 10 and a main reflecting element 11 around which are arranged subsidiary reflecting elements 12. In use all the elements ofthe arrangement are joined to provide a rigid structure, so that the entire arrangement may be secured to a building or aerial mast. The central direction of reception of the aerial is from the direction indicated by the arrow 13. However, reception is not from a narrow angle but over a range of angles of, say, 60 . The aerial may also be used for transmitting over the same 600 sector.

Figure 1 b shows a plan view ofthe aerial arrangement of Figure la.

Figure 2 shows a plan viewed a building 19 on which six aerials a,b,c,d,e and fare mounted in order to provide omni-directional coverage over a cell 20 of a cellular network. Adjacent cells 21,22,23,24,25 and 26 ofthe network are indicated.

Figure 3 shows a preferred embodiment of an apparatus according to the present invention. The apparatus comprises a body 41 and a elongate arm 42.The body41 hastwo slots 43 and 44which in use may be fitted to the reflecting and radiating elements of an aerial respectively, and fixed by quick release clamps such as are indicated at45 and 46. The arm 42 is rotatablyfixed to the body by means of a hinge 47 so that the arm may be rotated in a horizontal plane with respect to the body. The hinge 47 may comprise a bolt and wing-nut as shown, which may betightended to clamp the arm at a particular angle with respectto the body. The body is provided with an angular measurement scale 48, and the arm is provided with a pointer so the angle between the arm and the body may be easily determined.A short way from the body the arm has a further hinge 50 which allows rotation inthevertical plane, (an angular measurement scale 51 could again be provided so thatthe angle subtended may easily be set). A bolt and wing-nut 52 may be used to clamp the arm at any desired angle. Immediately after the hinge 50 a mounting 53 holds a sighting plate 54 above the arm.

At the remote end of the arm 42 (perhaps 75cm from the body) another sighting plate 55 is mounted.

Referring nowto Figure4a preferred method of aligning aerials according to the invention will be de scribed. Figure 4a shows a simplified plan viewof the apparatus of Figure 3, and Figure 4b shows the apparatus when the arm 42 has been rotated in the horizontal plane about hinge 47. Figure 4c shows a simplified side-view ofthe appartus of Figure 3, and Figure 4d shows the apparatus when the arm 42 has been rotated in the vertical plane about hinge 50.

The first step in the preferred aligning method is to consult a map of the location ofthe aerial. A position is selected from where an observer may conveni entlysee the aerial in situ, perhaps using binoculars.

The direction ofthe observer from the aerial is then calculated from the map. The apparatus shown in Figure 3 is taken and the arm 42 is rotated in the hori zontai plane as shown in Figure 4b such that, when the body is attached to the elements of the aerial,the arm 42 will be directed towards the observation point when the aerial is correctly oriented. The apparatus of Figure 3 is then mounted on the aerial.

An observer at the selected position will watch the aerial and be in communication with those working to orient it, perhaps bywalkie-talkie. The sighting boards 54 and 55 mounted on the arm 42 aretri angular in shape and are arranged such thattheir apexes point directly at each other, as shown in Figure 4e, when the arm is viewed directly end on.

The observer give directions to those working to or ientthe aerial to rotate the arm 42 in the vertical plane until he can see both sighting boards 54 and 55. Then he will give further directions to rotatethe aerial until, by consideration of the parallaxeffectbe- tween the sighting boards 54 and 55, it appears to be correctly oriented, at which time from his viewpoint the apexes of sighting boards 54 and 55 will be coincident (as shown in Figure4e).

Various improvements and embeliishments may be added to the apparatus of Figure 3 without ex ceeding the scope of the invention, for example, the apparatus may be madeto be collapsible; thearm may fold back against the body by rotating about hinge 50; and the sighting boards 54 and 55 may be collapsibly mounted so that they fold flat againstthe arm. The sighting boards 54 and 55, as described, are triangular in shape, however, in practice any suitable target arrangement may be used. Also, it may be useful to mount gun-sights onto the arm to assist in orienting it.

Furthermore various improvements and refinements may be provided to the method of aligning aerials without exceeding the scope ofthe invention.

For example, the relative positions in space of the aerial and observation points may equallywell, be measured using range-finding apparatus. Also the relative elevations of the observation point and aerial and the distance between them may be calculated, or measured, so that the arm 42 may be subtended in the vertical plane to the correct viewing angle before the apparatus of Figure 3 is mounted on the aerial.

Claims (9)

1. An apparatus for aligning aerials, comprising a body and an elongate arm rotatably interconnected such that the arm may be rotated in the horizontal plan relative to the body; the body bearing fixing meansforattachmentto an aerial, and bearing scale means by which the angular relationship between the body and arm may be measured; the arm bearing parallax effect target means by which its orientation may be determined by a remote observer.

2. An apparatus as claimed in claim 1 in which the body and arm are rotatably interconnected such that the arm may also be rotated in the vertical plane relative to the body.

3. An apparatus as claimed in claim 1 or 2 in which the parallax effect target means compriss a first triangular plate mounted above the arm adjacent to the rotatable interconnection, and a second triangular plate mounted at the end ofthe arm remote from the body; the two triangles bearing arranged such that an apex of the first triangle appears coincident with an apex of the second triangle when the arm is viewed end-on by a remote observer.

4. An apparatus as claimed in any preceding claim inwhich the arm may be folded towards the body and the target means folded against the arm when the apparatus is not in use.

5. An apparatus as claimed in any preceding claim for aligning aerials of the type having afirst substantially vertical tubular element, and a second tubular element disposed in parallel to the first; the fixing means ofthe body of the apparatus comprising two slots and two clamps, and when attached to the aerial the first and second elements are located one in each slot and locked in place one by each clamp.

6. A method of aligning aerials using an apparatus as claimed in any preceding claim comprising the steps of: selecting an observation point in the locality of the aerial; determining the direction of the observation point from the aerial with respect to a reference direction; arranging the arm at an angle relative to the body in accordance with the determination such that, if the body were attached to the aerial, the arm would point in the direction of the observation pointwhen the aerial was correctly aligned with respect to the reference direction; attaching the bodyto the aerial; adjusting the alignment ofthe aerial until the observer at the observation point, after consideration of the parallax effect of the target means, signals that the arm of the apparatus is oriented in the direction of the observation point.

7. A method as characterised in claim 6 when using an apparatus as claimed in claim 2 to 5 and in which after arranging the arms at an angle in accordance with the determination, the arm is arranged at an angle in the vertical plane such that when the body is attached to the aerial the target means is conveniently displayed to an observer at the same relative elevation as the observation point.

8. An apparatusforaligning aeriaisashere- inbefore described with reference to Figures 3 and 4 ofthe accompanying drawings.

9. A method of aligning aerials as hereinbefore described using an apparatus as claimed in claim 8.