GB2201293A

GB2201293A - Aerial sub-reflector mounting structure

Info

Publication number: GB2201293A
Application number: GB08800588A
Authority: GB
Inventors: Edmund Colin Johnston; Peter May
Original assignee: British Telecommunications PLC
Current assignee: British Telecommunications PLC
Priority date: 1987-01-15
Filing date: 1988-01-12
Publication date: 1988-08-24
Anticipated expiration: 2008-01-12
Also published as: GB2201293B; GB8700887D0; GB8800588D0

Abstract

An aerial sub-reflector mounting structure (4) comprises a tripod (5, 6, 7), bipod (8, 9) and monopod (10) in which each of the six legs is of variable length. This structure has the advantages that changes in the position or orientation of the sub-reflector (2) may be effected while the sub-reflector remains completely supported by the mounting structure. Preferably the legs of the structure comprise two threaded bars joined by bottle screws or turn buckles. <IMAGE>

Description

AERIAL SUB-REFLECTOR MOUNTING STRUCTURE This invention relates to an aerial sub-reflector mounting structure. In particular, it relates to a mounting structure which includes facilities which allow adjustments of position and orientation of the sub-reflector.

Figure 1 illustrates a typical known aerial including a main reflector 1 and sub-reflector 2 mounted at the end of a tower, or arm, 3 by means of a mounting structure 4.

Gross position adjustments of the sub-reflector are made at the base of the tower 3. The fine adjustments of the position and orientation are made at the sub-reflector mounting structure 4.

A known sub-reflector mounting structure 4 comprises two plates; the first is connected to the sub-reflector 2 and the second is connected to the end of the tower 3.

Each plate has four slots. The plates are oriented so that the slots of the first plate are at right-angles to the slots of the second, and the plates are connected by four threaded bars. Each threaded bar connects one slot in the first plate with the corresponding slot on the second plate by means of four nuts, two of which are tightened on either side of the slot on the first plate, and the other two of which are tightened on either side of the slot on the second plate. When all sixteen nuts have been tightened, the sub-reflector 2 is rigidly held at the end of the tower 3. To effect any changes in position or orientation of the sub-reflector the nuts holding the plates have to be loosened.Then to change position, the sub-reflector is moved from side to side or up and down, by sliding the bars in the slots, and the nuts re-tightened in new positions; to change orientation the nuts are re-tightened so that the two plates lie in planes at the requisite angle with respect to each other.

The disadvantage of this type of sub-reflector mounting structure is that to effect changes in position or orientation of the sub-reflector requires many of the nuts to be loosened so that the sub-reflector is not restrained from moving by the mounting structure while the adjustment is carried out. Another means of supporting the sub-reflector and positioning and orientating it correctly must be employed all the time the nuts are not tightened. Since the sub-reflector may weigh up to half a ton, this presents great practical difficulties in making fine adjustments to the position or alignment of the sub-reflector.

Another disadvantage with the known mounting structure is that when the sub-reflector is orientated at any angle that requires the first and second plates not to be parallel then the threaded bars are bent by the force exerted when the nuts are tightened.

According to the invention there is provided an aerial sub-reflector mounting structure comprising six struts, each in use interconnecting the sub-reflector and a support arm, wherein three of the struts are arranged as a tripod, another two of the struts are arranged as a bipod, and the remaining strut is a monopod; and wherein each of the six struts is of variable length.

Preferably each strut consists of two threaded members joined by a bottle screw. Advantageously each strut includes connectors at both ends about which the strut may rotate.

According to another aspect of the invention there is provided an aerial including a sub-reflector and a support, the support comprising three mutually perpendicular adjustable screw members connected in series, the free end of one screw member supporting the sub-reflector, so that the position of the sub-reflector may be varied independently in any one of three orthogonal directions by turning only one of the three screw members.

The invention will now be described by way of example with reference to the following figures in which: Figure 2 is a perspective schematic drawing illustrating an embodiment of the invention; Figure 3 is a perspective drawing illustrating a preferred embodiment of the invention; Figure 4 is a side view of the embodiment of figure 3; Figure 5 is a perspective schematic drawing illustrating a further embodiment of the invention; Figure 6a is a plan view of a further embodiment of the invention, and, Figure 6b is an end elevation of the embodiment of figure 6a, with some detail ommitted and the central portion sectioned along line A-A.

Referring now to figure 2, the sub-reflector 2 is supported at three points A, B and C. At point A the sub-reflector is supported by a tripod consisting of legs or struts 5, 6 and 7; each of these legs is of variable length, and each leg is free to rotate in any plane, about either of its ends. The tripod support controls three degrees of freedom and allows the location of point A on the sub-reflector to be set in its correct absolute position in space. Point A may be moved up, down and sideways to any position within reach of the maximum leg length.

At point B the sub-reflector is supported by a bipod consisting of legs or struts 8 and 9; both of these legs are of variable length, and both are free to rotate about either end in any plane. The bipod support controls two degrees of freedom; the orientation of the subreflector, about point A, and also its tilt along the direction A B.

At point C the sub-reflector is supported by a monopod consisting of leg 10; of variable length, free to rotate about either end. The monopod support controls, the only remaining degree of freedom, tilt about the line A'to B.

Each of the six 3,ags 5, 6, 7, 8, 9 and 10 is of variable length, and may be telescopic or otherwise variable in any desired fashion. Preferably the legs consist of two separate struts each with threaded ends connected by a bottle screw or turn buckle. Stainless steel (18/8) fittings, as already developed and widely used in marine applications, may be employed. The bottle screws may be manually adjustable or motorised, in which case they may be controlled by a computer.

where the sub-reflector 2 is mounted approximately parallel to the mounting frame 4 , as is here shown in Figure 4, the legs may all be of equal length (in the extended or unextended condition). They can thus be made interchangeable, reducing manufacturing costs.

It should be appreciated that either the bipod or tripod or both may be inverted without adversely affecting the adjustability of the mounting structure. It may sometimes be advantageous to fabricate the structure with the tripod and bipod inverted with respect to each other since this means that five and four attachment points have to be provided on the sub-reflector and support respectively as opposed to three and six as shown in figure 2.

Once the sub-reflector has been mounted and secured by the tripod, bipod and monopod, adjustment or readjustement of the position or orientation may be carried out at any time simply by adjusting the bottle screws on one or more of the legs. This has the advantage that once the sub-reflector has been mounted it is always secured and supported by the support assembly, even during adjustment of the position or orientation. The mounting structure also has the advantage that it can support the sub-reflector in a wide variety of positions and orientations without any of the legs -experiencing bending forces.

Referring now to figure 3, the sub-reflector 2 (not shown) in this embodiment is rigidly attached to a 'T'-shaped bracket 11, and the support arm includes a 'figure-of-eight' shaped member 12 upon which the sub-reflector is mounted by the mounting frame 4. The tripod, consisting of legs 5, 6 and 7, is connected at its apex, point A, at bottom of the stem of the ZT'. The legs of the tripod are positioned in the bottom two corners of the 'figure-of-eight' and on the cross member in the centre of the 1figure-of-eight1 respectively. The bipod is positioned with its apex, point B, and one of the top corners of the figure-of-eight, and its legs at the junction of the stem and branches of the 'T' and on one of the branches of the 'T' respectively. The monopod is connected at the other upper corner of the figure-of-eight and on the other branch of the BT.

Figure 4 shows a side view of the assembly shown in figure 3, and includes the sub-reflector 2 shown attached to the 'T'-shaped member 11 and more of the sub-reflector support tower 3 of which the 'figure-of-eight' member 12 forms a part.

In figures 3 and 4 the telescopic nature of the arms 5-9 is indicated by two parallel lines drawn along either side of the centres of the arms.

It will be appreciated that the ends of the legs defining the tripod or bipod need not actually meet at a point but may be spaced apart by a small distance without substantially affecting the operation of the invention.

Referring now to figure 5, it is possible to position point A at the centre of the sub-reflector. This has the advantage of making adjustment easier since the distance between the sub-reflector and the reflector cantle varied independently of the dish inclination, but it does not in general provide such a rigid and satisfactory mounting since the triangle defined by the points A, B & C is smaller.

Accordingly, in this embodiment the central mounting may be as shown in Figures 6a and 6b. A plate 20 is secured to the mounting frame 12 and a plate 21 to the' sub-reflector 2, the two being connected by a moveable mounting. The mounting comprises a rectangular box 22, with two stubs 23a, 23b welded on opposite long sides.

One stub (23a) is threaded and the other (23b) is of square cross section (although a round cross section will suffice if the nuts are tight enough to prevent the stub rotating). The stubs 23a, 23b pass through brackets 24a, 24b, on plate 20, and threaded stub 23a is locked in a desired position relative to plate 20 by two lock nuts 25a & 25b.

The subreflector 2 (which is solid with plate 21) may thus be moved in the x direction (indicated on Figure 6) rightwards by loosening nut 25b, screwing nut 25a along so as to pull stub 23a through bracket 24a to the desired position and then re-tightening nut 25b. Stub 23a acts as a guide and strengthening bar.

Box 22 contains two aligned holes 26a, 26b, through its short sides, through which a rod 27 runs. The rod 27 has a threaded end 27a and a square unthreaded end 27b and between the ends a stub 28 is mounted on a rose bearing 29. The threaded end is locked in a desired position relative to box 22 by two lock nuts 30a, 30b and the vertical stub 28 (and hence plate 21 and the subreflector 2) may thus be moved in the y direction by loosening one nut and screwing the other up as described above. Stub 28 is threaded and passes through a hole 31 in plate 21.

Stub 28 is locked in position relative to places21 by two locking nuts 32a, 32b one on either side of the plate.

The distance apart of plates 21 and 20 and hence the position in the z direction of the subreflector is adjusted as described above by loosening one nut and screwing the other up. It will, of course, be appreciated that plate 20 could be connected to the subreflector 2 and plate 21 to the mounting frame 12 without altering the working of the box.

The screwed stubs need not be mutually perpendicular as shown, but the perpendicular arrangement allows independant adjustment in the x, y & z directions by turning a single screw.

Claims

CLAINS

1. An aerial sub-reflector mounting structure comprising six struts, each in use interconnecting the sub-reflector and a support arm, wherein the three of the struts are arranged as a tripod, another two of the struts are arranged as a bipod, and the remaining strut is a monopod; and wherein each of the six struts is of variable length.

2. An aerial sub-reflector mounting structure as claimed in claim 1, wherein the extended length of all such struts are substantially equal so that the struts are interchangeable.

3. An aerial sub-reflector mounting structure as claimed in claim 1 or claim 2 wherein each strut consists of two threaded embers joined by a bottle screw or turn buckle.

4. An aerial sub-reflector mounting structure as claimed in claims 1, 2 or 3 wherein each strut includes connectors at both ends about which the strut may rotate.

5. An aerial sub-reflector mounting structure as claimed in any. one of claims 1 to 4 wherein the tripod and bipod are inverted with respect to each other.

6. An aerial including a sub-reflector mounting structure as claimed in any preceding claim.

7. An aerial as claimed in claim 5 wherein the sub-reflector includes a 'T'-shaped backing member, and - the support arm includes a 'figure-of-eight' shaped supporting member; and the sub-reflector mounting structure comprises a tripod with its apex connected to the bottom of the stem of the 'T' and its legs connected to the bottom two corners of the 'figure-of-eight' and to the central cross member respectively; the bipod is connected with its apex to one of the upper corners of the 'figure-of-eight' and its legs connected to the junction of the stem and branches of the 'T'*and one of the branches of the 'T' respectively; and the monopod is connected to the other corner of the 'figure-of-eight' and the other branch of the 'T'.

8. An aerial including a sub-reflector and a support, the support comprising three mutually perpendicular adjustable screw members connected in series, the free end of one screw member supporting the sub-reflector, so that the position of the sub-reflector may be varied independently in any one of three orthogonal directions by turning only one of the three screw members.

9. An aerial sub-reflector mounting structure substantially as described herein and with reference to Figures 2 to 4.

10. An aerial sub-reflector mounting structure substantially as described herein and with reference to Figures 6a and 6b.