US3860931A - Ship-borne gravity stabilized antenna - Google Patents
Ship-borne gravity stabilized antenna Download PDFInfo
- Publication number
- US3860931A US3860931A US418908A US41890873A US3860931A US 3860931 A US3860931 A US 3860931A US 418908 A US418908 A US 418908A US 41890873 A US41890873 A US 41890873A US 3860931 A US3860931 A US 3860931A
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- antenna
- ship
- axes
- arrangement
- antenna arrangement
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q1/00—Details of, or arrangements associated with, antennas
- H01Q1/12—Supports; Mounting means
- H01Q1/18—Means for stabilising antennas on an unstable platform
Definitions
- ABSTRACT [52] US. Cl 343/709, 343/765, 343/872,
- a ship-borne antenna system for a maritime satellite communications service should have a high gain in order to minimise the satellite power requirements (and hence satellite costs) for the satellite-to-ship communications link.
- the gain increases, the beamwidth narrows and the allowable limits of the antenna orientation converge. Any ship at sea will, in anything other than a flat calm, roll and pitch to some extent and clearly if the degrees of roll and pitch are greater than the beamwidth of the antenna system the antenna orientation will need to be controlled if an adequate communications capability is to be maintained.
- the beam-edge gain relative to isotropic is 6 dB, and the corresponding figures for a 1 m diameter dish and a 2% m diameter dish are 18 dB and 26 dB respectively.
- the beamwidths (to the 3 dB points) of these antennae are 64, and 6 respectively. Trawlers are known to roll to more than i 35 and hence some control on the antenna orientation would be required even when using a modest 6 dB gain single helix antenna.
- the invention provides a gimballed-platform-mounted antenna arrangement for semi-stabilizing the orientation of the antenna of said arrangement on a ship, said arrangement being semistabilized in use by means of its having a long natural period of oscillation and a high moment of inertia as hereinbefore defined.
- a long period of oscillation is hereby defined as a period of oscillation longer than the longest significant period of the periodic components of motion the ship in the sea.
- a high moment of inertia is hereby defined as a moment of inertia sufficiently large that the amplitude of angular periodic motion induced in the antenna arrangement by translational periodic motion of the ship in the sea is at most of comparable magnitude to the amplitude of angular periodic motion induced in the antenna arrangement by angular periodic motion of the ship in the sea.
- the natural period of oscillation may be at least two, and preferably two and a half, times the longest significant period of oscillation of the ship in the sea so that the degree of coupling from the motion of the ship to that of the arrangement will be reduced.
- the invention comprises a structure of mass M kg including a directional receiving antenna, said structure being pendulously mounted upon the ship by hearing means having two axes intersecting at a pivotal centre, the arrangement being such that about each axis the total Coulomb friction torque T Nm of the bearing means is related to the moment of inertia I kgm of the structure by the expression T/! s 7.5 X 10" N/kgm and the center of gravity of the structure is displaced below the pivotal center by a distance L, where L 2 X 10 I/M m.
- the structure may include means for directing the antenna to a predetermined orientation, the directing means preferably including azimuth directing means for directing the antenna in azimuth and elevation directing means for directing the antenna in elevation.
- the azimuth directing means can, in use, be operatively associated with a compass of the ship so that the azimuthal setting of the antenna is maintained, thus to compensate for yaw and changes of course of the ship.
- FIG. 1 is a diagrammatic representation of the phase relationship between transverse, translational, and angular periodic motions of a ship and angular periodic motion induced thereby in a pendulous structure mounted on the ship;
- FIG. 2 is a diagrammatic representation of the relationship between antenna beamwidth and required stability for a pendulously mounted antenna
- FIG. 3 is a schematic representation in front elevation of an antenna arrangement according to the invention.
- FIG. 4 is a partial side elevation corresponding to FIG. 3;
- FIG. 5 shows a tested gimballed platform assembly for an antenna arrangement according to the invention.
- FIG. 6 is a partial cross-section through the assembly of FIG. 5.
- Pitch is an angular fluctuation about a beam-wise axis.
- Surge is a longitudinal translational fluctuation, that is to say movement along a line ahead/astern.
- Roll is an angular fluctuation about a longitudinal axis and sway. is a beam-wise translational fluctuation.
- the ship as indicated at 10 is at one extreme of its sway movement, i.e., it is at its maximum displacement from its general line of progress in the plane indicated at 11. At this point, its acceleration is in the direction of arrow 12.
- Sway which arises when the ship is in a beam-sea with the waves meeting it sideon, is caused partly by the tendency of the ship to slide down the wave and partly by the circular motion of the water in the wave, and occurs in association with rolling of the ship so that by the time the ship passes through the plane 11, it has taken up an attitude as indicated at 13.
- the ship has reached its other extremity of sway as indicated at 14, it is again substantially vertical. At this other extremity it is subject to an acceleration in the direction of arrow 15.
- the pendulous structure is pivotally mounted about the roll-centre of the ship, that is to say the line about which the ship rolls, the roll of the ship will cause the pendulous structure to have an additional beam-wise translational fluctuation.
- the amplitude of fluctuations induced in the pendulous structure by the sway of the ship can be reduced by providing a frictional damping torque at its pivot. This would, however, increase the coupling between angular movement of the pendulous structure and angular movement of the ship so that the amplitude of fluctuation induced in the pendulous structure by the roll of the ship would be increased. It is therefore necessary to seek some means, other than controlling the pivot friction, which will limit the sway-induced fluctuation without simultaneously increasing the. rollinduced fluctuation. In the present invention, this is accomplished by arranging the pendulous structure of the gimballed-platform-mounted antenna arrangement to have a high moment of inertia and a long period of oscillation as hereinbefore defined.
- the required limitation on the amplitude of fluctuation of a gimballed-platform-mounted antenna arrangement can be determined by considering FIG. 2.
- the line 20 represents the actual orientation of a communications satellite relative to the ship and the line 21 represents the orientation of the antenna, at one extreme limit of its angular oscillation.
- the angle A is the allowable angular stability of the antenna
- the angle B is the beamwidth of the antenna to the 3 dB points
- angle C is an angular tolerance obviating the need for continuous resetting of the antenna pointing direction.
- a fast ship steaming on a great circle route can travel every hour through a distance large enough for the orientation of a geo-stationary satellite relative to the ship to change by as much as 1 per hour. It is assumed that it is reasonable to require that the direction of the antenna be re-set every hours and thus an angular tolerance of 5 must be included in estimating the required stability of the antenna. In other words, it is assumed that the angle C equals 5.
- the beamwidth of a l m diameter dish antenna is and it follows from this that the required stability for such an antenna is i 5.
- An antenna arrangement with parameters of these values will achieve the desired stability of i 5 when borne on a cargo ship of 14,000 tons dead weight, beam-on to the prevailing sea in a Beaufort 9 wind.
- a system with parameters of these values will also attain the desired stability when mounted on a trawler in similar sea and wind conditions. It is expected that the desired stability could be maintained under the above described adverse conditions, for more than 99 percent of the time.
- the parameter ML/I is easily arranged to have the correct value since the parameter L, being simply the distance between the center of oscillation and the center of gravity of the system, may be varied at will.
- the parameter T is therefore the critical factor.
- a needle roller bearing of nominal diameter about 4 cm will give a value of TH equal to the limiting value above and since the loads imposed on the bearing by a system with parameters of the above values can be adequately supported by a needle roller bearing having a diameter of only about 0.5 centimeters, it follows that one can arrive at a suitable design by using needle roller bearings of diameters between these limits.
- FIGS. 3 and 4 show schematically an antenna semi-stabilized orientation arrangement having parameters which satisfy the foregoing requirements.
- the antenna structure indicated generally at 23, is in the form of a l m diameter dish 24 pivotally mounted at 25 at the upper end of an up-standing arm 26.
- Elevation directing means in the form of a remotely controlled electric motor indicated at 35a is provided for rotating the dish 24 about the pivot 25 to enable its elevation to be set and re-set.
- a support 27 is rigidly secured to the lower end of the arm 26.
- the antenna assembly comprising the dish 24, arm 26 support 27 and motor 35a is mounted upon a platform 28 and azimuth directing means in the form of a remotely controlled electric motor 35b is provided for rotating the antenna assembly about an axis normal to the interface between the support 27 and the platform 28.
- the interface between the support 27 and the platform 28 will be substantially horizontal so that the azimuth directing means will be operable to rotate the antenna assembly about a generally vertical axis.
- the azimuth directing means is coupled to the ships compass and thereby controls the bearing of the antenna to compensate for yaw and changes of course.
- the platform 28 is gimbally mounted by means of a universal joint assembly 29 upon some rigid part of the structure of the ship indicated at 30.
- the part 30 may be a mast or may be part of the bridge structure.
- the universal joint assembly 29 has a pair of orthogonal axes arrange to lie respectively parallel to the major horizontal axes of the ship, i.e., the longitudinal (ahead/astern) axis and the beam-wise axis.
- a gimbal mounting such as a universal joint may be regarded as having axes intersecting at a pivotal center," by which is meant a point about which a structure mounted on the joint is constrained to rotate.
- Extending outwards from the platform 28 are four limbs 31 arranged in two orthogonal planes.
- a weight 32 is secured to the outer end of each limb 31.
- the four weights 32 are of substantially equal mass and serve a two-fold purpose: they are of sufficient mass and suitably disposed to give the arrangement a pendulous structure pivotally mounted on the universal joint assembly 29 and having a long period of oscillation; and their masses and their distances from the pivotal centre of the universal joint assembly 29 are such that the arrangement has a high moment of inertia.
- the dish 24 is substantially counter-balanced by a counterbalance mass 33 so that changes in the elevation of the dish will not significantly alter the moment of inertia of the arrangement or the centre of gravity of the struc ture.
- Each of the weights 32 is of mass 25 kg and they are arranged so that the centre of gravity of the arrangement lies approximately three-fourths mm below its pivotal center. Such an arrangement has a moment of inertia of approximately 30 kg m and a period of oscillation of approximately 45 s.
- the arrangement is covered by a radome indicated at 34 which prevents wind forces disturbing the setting of the antenna and protects the arrangement from the maritime environment.
- the radome may be constructed of any material which is structurally adequate and transparent to electromagnetic radiation of the working frequency, which in the present case is about 1.6 GHz.
- the described arrangement is such that the antenna may be stabilized to within i 5 for ships ranging from trawlers to tankers in virtually in all sea conditions.
- This degree of stability would enable the ship to use an antenna as large as a l m diameter dish, which is considered to be a sensible upper size limit for antenna to be fitted in a suitable position to the majority of oceangoing vessels.
- stabilization to within about :t 7? should be achievable, and this would allow the use of a quad helix antenna having a beam-edge gain of 16 dB.
- Use of a quad helix antenna would have the advantage that the size of the radome, and hence the cost of the assembly, can be reduced.
- the period of such motions will either be so short (e.g., vibration from the ships engines) as to have an insignificant effect upon the stability of the arrangement or so long (e.g., tidal movements of the sea) as to feed energy into the system at a rate which can be dissipated by the pivot friction.
- the moment of inertia of the structure is sufficiently large for the effect of, for instance, variations in the bearing friction and the resilience of the motor leads 36 to be negligible.
- FIG. 5 shows a gimballed platform assembly which has been tested.
- the platform comprises a bearing housing 37 and four weighted arms 38 extending therefrom.
- the upper face of the housing 37 is adapted to receive and carry a support such as that indicated at 27 in FIGS. 3 and 4.
- a weight 39 is screwed on to the end of each arm 38 and is locked in a desired position thereon by means of a lock nut 40.
- Each weight 39 is lead-filled and has a mass of approximately 30 kg.
- the arms 38 are arranged in two coaxial, mutually orthogonal pairs and the weights 39 of each pair are about 1.4 m apart.
- the platform is supported by means of a universal joint within the housing 37 upon a stanchion 11 which is adapted to be rigidly secured to some part of the superstructure of a ship.
- One link of the joint is secured to the upper end of the stanchion 11 and the other is secured against the underside of a spacer 42 shown in FIG. 6.
- spacers of different vertical dimension can be employed to vary the position of the platform and antenna assembly vertically relative to the pivotal center of the universal joint, so that the arrangement is adjustable to cater for antennae of differing size and form or, where desired, to balance the platform alone.
- a spacer was used which located the center of gravity of the assembly 075 mm below the pivotal center of the universal joint.
- the joint employed was a proprietary item having needle roller bearings of about ll mm nominal diameter. The moment of inertia of the tested assembly was a little over 29 kg m.
- the stanchion 11 was secured on the flying bridge of an unstabilized ship of approximately 1,450 tons deadweight fitted with a gyro-horizon device giving an accurate reference to a true horizontal plane.
- the platform was instrumented using low-friction angular position transducers and the outputs therefrom were arranged to be combined with the outputs of the gyro-horizon device to yield information on the instantaneous rolland pitch of the platform relative to the true horizontal plane.
- the instantaneous angles of roll and pitch of the platform were subsequently combined vectorially to give the absolute angle or tilt of the platform at each instant.
- the tilt angles were subjected to statistical analysis and a histogram was plotted.
- the histogram shows that the platform tilt angle exceeded i 5 for only 0.15 percent of the time during which results were recorded, although it should be noted that this is, of course, strongly dependent upon the temporal variation of the sea conditions during that time.
- a truer indication of the stabilizing effect is given by the fact that, in pitch, the ship exceeded i 5 for 0.13 percent of the time while the pitch (that is, fore and aft) angle of the platform exceeded 5 for only 0.05 percent of the time. Further, whilst the pitch angle of the ship exceeded i 10 for 0.015 percent of the time, the pitch angle of the platform exceeded 10 for only 0.001 percent of the time. It is apparent that the platform was markedly more stable than the ship.
- a system for semi-stabilizing orientation of a directional receiving antenna of an antenna arrangement of a ship comprising: a structure having a mass of M kg and including said antenna balanced about a point fixed with respect to said structure; bearing means which define axes of rotation for said structure, which axes intersect at a pivotal center; and a radome covering said structure; said structure being, in use, gimbally mounted pendulously upon said ship by said bearing means with the center of gravity of said structure located below said pivotal center and spaced therefrom by a distance which, in meters, does not exceed 0.002 times the minimum value of the quotient I/M, where Ikg m is the moment of inertia of said structure about any of said axes, and said bearing means has a maximum total Coulomb friction torque about any of said axes which, in Newton-meters, is not greater than 0.00075 X l.
- An antenna arrangement according to claim 1 including means for adjusting the location of said center of gravity relative to said pivotal centre.
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Abstract
Description
Claims (5)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US418908A US3860931A (en) | 1973-11-26 | 1973-11-26 | Ship-borne gravity stabilized antenna |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US418908A US3860931A (en) | 1973-11-26 | 1973-11-26 | Ship-borne gravity stabilized antenna |
Publications (1)
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US3860931A true US3860931A (en) | 1975-01-14 |
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US418908A Expired - Lifetime US3860931A (en) | 1973-11-26 | 1973-11-26 | Ship-borne gravity stabilized antenna |
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Cited By (18)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3968496A (en) * | 1974-03-04 | 1976-07-06 | International Standard Electric Corporation | Stabilized antenna platform |
US4143378A (en) * | 1977-04-18 | 1979-03-06 | The United States Of America As Represented By The Secretary Of The Department Of Transportation | Pendulum antenna |
US4491388A (en) * | 1982-05-28 | 1985-01-01 | Wood Douglas E | Support carriage for a solar concentrator |
US4512448A (en) * | 1981-09-25 | 1985-04-23 | Thomson-Csf | System for equilibrating an imbalance couple and use of such a system for equilibrating an airborne radar antenna |
US4596989A (en) * | 1983-02-14 | 1986-06-24 | Tracor Bei, Inc. | Stabilized antenna system having an acceleration displaceable mass |
US4609083A (en) * | 1983-03-31 | 1986-09-02 | Stuhler William B | Reactive attitude stabilization system |
US4920349A (en) * | 1983-08-03 | 1990-04-24 | Centre National D'etudes Des Telecommunications | Antenna mounting with passive stabilization |
US5111212A (en) * | 1990-01-30 | 1992-05-05 | Questus Corporation | Radar antenna mount |
US5313219A (en) * | 1992-01-27 | 1994-05-17 | International Tele-Marine Company, Inc. | Shipboard stabilized radio antenna mount system |
US5410327A (en) * | 1992-01-27 | 1995-04-25 | Crescomm Telecommunications Services, Inc. | Shipboard stabilized radio antenna mount system |
US5512912A (en) * | 1994-01-28 | 1996-04-30 | Amsc Subsidiary Corporation | Marine antenna mount |
US5517205A (en) * | 1993-03-31 | 1996-05-14 | Kvh Industries, Inc. | Two axis mount pointing apparatus |
US5922039A (en) * | 1996-09-19 | 1999-07-13 | Astral, Inc. | Actively stabilized platform system |
US20050035263A1 (en) * | 2001-10-19 | 2005-02-17 | Cesar Colavecchi | Devices that are used to support the poles of parasols, antennae and other elements |
RU2449433C1 (en) * | 2011-02-04 | 2012-04-27 | Валерий Викторович Степанов | Device for nondirectional antenna stabilisation |
RU2479897C2 (en) * | 2011-04-26 | 2013-04-20 | Открытое акционерное общество "Конструкторское бюро "Аметист" (ОАО "КБ "Аметист") | Antenna post for radar station |
US20170025839A1 (en) * | 2015-07-23 | 2017-01-26 | At&T Intellectual Property I, Lp | Antenna support for aligning an antenna |
US10897072B2 (en) * | 2018-09-28 | 2021-01-19 | Robert N. Iannuzzi | Balance platform for mobile antenna |
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US1260181A (en) * | 1917-06-06 | 1918-03-19 | John Garnero | Self-leveling table. |
US1569325A (en) * | 1922-08-08 | 1926-01-12 | Drahtlose Telegraphie Gmbh | Radio direction finder |
US2477574A (en) * | 1947-07-21 | 1949-08-02 | Sperry Corp | Gyro vertical |
US2599381A (en) * | 1950-01-21 | 1952-06-03 | Collins Radio Co | Axis converter |
US2901208A (en) * | 1957-01-11 | 1959-08-25 | Collins Radio Co | Stabilized load |
US3789414A (en) * | 1972-07-19 | 1974-01-29 | E Systems Inc | Pendulum stabilization for antenna structure with padome |
-
1973
- 1973-11-26 US US418908A patent/US3860931A/en not_active Expired - Lifetime
Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
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US1260181A (en) * | 1917-06-06 | 1918-03-19 | John Garnero | Self-leveling table. |
US1569325A (en) * | 1922-08-08 | 1926-01-12 | Drahtlose Telegraphie Gmbh | Radio direction finder |
US2477574A (en) * | 1947-07-21 | 1949-08-02 | Sperry Corp | Gyro vertical |
US2599381A (en) * | 1950-01-21 | 1952-06-03 | Collins Radio Co | Axis converter |
US2901208A (en) * | 1957-01-11 | 1959-08-25 | Collins Radio Co | Stabilized load |
US3789414A (en) * | 1972-07-19 | 1974-01-29 | E Systems Inc | Pendulum stabilization for antenna structure with padome |
Cited By (19)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3968496A (en) * | 1974-03-04 | 1976-07-06 | International Standard Electric Corporation | Stabilized antenna platform |
US4143378A (en) * | 1977-04-18 | 1979-03-06 | The United States Of America As Represented By The Secretary Of The Department Of Transportation | Pendulum antenna |
US4512448A (en) * | 1981-09-25 | 1985-04-23 | Thomson-Csf | System for equilibrating an imbalance couple and use of such a system for equilibrating an airborne radar antenna |
US4491388A (en) * | 1982-05-28 | 1985-01-01 | Wood Douglas E | Support carriage for a solar concentrator |
US4596989A (en) * | 1983-02-14 | 1986-06-24 | Tracor Bei, Inc. | Stabilized antenna system having an acceleration displaceable mass |
US4609083A (en) * | 1983-03-31 | 1986-09-02 | Stuhler William B | Reactive attitude stabilization system |
US4920349A (en) * | 1983-08-03 | 1990-04-24 | Centre National D'etudes Des Telecommunications | Antenna mounting with passive stabilization |
US5111212A (en) * | 1990-01-30 | 1992-05-05 | Questus Corporation | Radar antenna mount |
US5313219A (en) * | 1992-01-27 | 1994-05-17 | International Tele-Marine Company, Inc. | Shipboard stabilized radio antenna mount system |
US5410327A (en) * | 1992-01-27 | 1995-04-25 | Crescomm Telecommunications Services, Inc. | Shipboard stabilized radio antenna mount system |
US5517205A (en) * | 1993-03-31 | 1996-05-14 | Kvh Industries, Inc. | Two axis mount pointing apparatus |
US5512912A (en) * | 1994-01-28 | 1996-04-30 | Amsc Subsidiary Corporation | Marine antenna mount |
US5922039A (en) * | 1996-09-19 | 1999-07-13 | Astral, Inc. | Actively stabilized platform system |
US20050035263A1 (en) * | 2001-10-19 | 2005-02-17 | Cesar Colavecchi | Devices that are used to support the poles of parasols, antennae and other elements |
RU2449433C1 (en) * | 2011-02-04 | 2012-04-27 | Валерий Викторович Степанов | Device for nondirectional antenna stabilisation |
RU2479897C2 (en) * | 2011-04-26 | 2013-04-20 | Открытое акционерное общество "Конструкторское бюро "Аметист" (ОАО "КБ "Аметист") | Antenna post for radar station |
US20170025839A1 (en) * | 2015-07-23 | 2017-01-26 | At&T Intellectual Property I, Lp | Antenna support for aligning an antenna |
US10784670B2 (en) * | 2015-07-23 | 2020-09-22 | At&T Intellectual Property I, L.P. | Antenna support for aligning an antenna |
US10897072B2 (en) * | 2018-09-28 | 2021-01-19 | Robert N. Iannuzzi | Balance platform for mobile antenna |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: BRITISH TELECOMMUNICATIONS Free format text: THE BRITISH TELECOMMUNICATIONS ACT 1981 (APPOINTED DAY) ORDER 1981;ASSIGNOR:POST OFFICE;REEL/FRAME:004976/0307 Effective date: 19871028 Owner name: BRITISH TELECOMMUNICATIONS Free format text: THE BRITISH TELECOMMUNICATIONS ACT 1981 (APPOINTED DAY) ORDER 1981;ASSIGNOR:POST OFFICE;REEL/FRAME:004976/0248 Effective date: 19871028 Owner name: BRITISH TELECOMMUNICATIONS PUBLIC LIMITED COMPANY Free format text: THE BRITISH TELECOMMUNICATION ACT 1984. (APPOINTED DAY (NO.2) ORDER 1984.;ASSIGNOR:BRITISH TELECOMMUNICATIONS;REEL/FRAME:004976/0259 Effective date: 19871028 Owner name: BRITISH TELECOMMUNICATIONS PUBLIC LIMITED COMPANY Free format text: THE TELECOMMUNICATIONS ACT 1984 (NOMINATED COMPANY) ORDER 1984;ASSIGNOR:BRITISH TELECOMMUNICATIONS;REEL/FRAME:004976/0276 Effective date: 19871028 Owner name: BRITISH TELECOMMUNICATIONS PUBLIC LIMITED COMPANY Free format text: THE BRITISH TELECOMMUNICATIONS ACT 1984. (1984 CHAPTER 12);ASSIGNOR:BRITISH TELECOMMUNICATIONS;REEL/FRAME:004976/0291 Effective date: 19871028 |