Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Patent
1993-11-05
1995-10-10
Hellner, Mark
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
342 75, H01Q 312
Patent
active
054574641
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method and means for monitoring alignment of a receiver of electro-magnetic radiation with a source of electro-magnetic radiation. More particularly, but not exclusively, the present invention relates to a method and means for monitoring and maintaining alignment of a satellite transmission receiver dish and a satellite transmitter when either or both the source and the receiver are not geostationary.
BACKGROUND TO THE INVENTION
Receivers for satellite television generally comprise a parabolic dish having a dipole at its centre to collect the high frequency electro-magnetic radiation transmissions from a satellite television transmitter in geostationary orbit. The effectiveness of reception by the receiver is heavily reliant upon maintenance of alignment of the dish with the transmitter. This poses a considerable problem where the satellite receiver dish is mounted to a vehicle or vessel, such as a ship, which is moving relative to the surface of the earth.
Amongst the systems which have been developed to overcome this problem are a simple gyroscopic mounting for use on sea-going vessels to compensate for rolling motion of the vessel, and a system which has been developed for use on buses which comprises a sensory device having three zones positioned to enable detection of two axes of skew of the signal received from the transmitter by comparing the time delay in reception of signal by each of the zones. Neither of these systems is suitably rapid, efficient and effective in operation.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a tracking system for enabling maintenance of alignment between a receiver of electro-magnetic radiation and a source of electro-magnetic radiation signals, the system comprising: a receiver; a sensor associated, in use, with the receiver to sense the strength of the signal received by the receiver; and an interrupter device, which in use, intermittently interrupts one or more discontinuous eccentric portions of the signal being received by the receiver thereby attenuating the received signal by an extent which is dependent upon the degree of misalignment of the receiver from the transmitter.
Preferably means are provided to synchronise operation of the sensor with operation of the interrupter device.
Preferably the interrupter device interrupts a pair of portions of the signal received.
Preferably the pair of portions are substantially radially opposing.
Yet more preferably, the interrupter device interrupts two pairs of portions, each pair lying substantially along a respective one of the transverse horizontal (side-to-side) and vertical (top-to-bottom) axes of the receiver.
Preferably the system further comprises an automatic comparator for comparing the received signal as attenuated by interruption of one of said pair of radially opposing with the received signal as attenuated by interruption of the other of said pair and providing an output signal corresponding to the difference between each compared pair of received signals.
Preferably the system further comprises an orthomode transducer and a pair of receiver elements.
The system suitably further comprises a corrective transport mechanism which acts to re-align the receiver with the transmitter in response to control signals which correspond to the output signals from the comparator.
Preferably the receiver is of cassograin-type and the interrupter device comprises a reflector onto which the dish of the receiver focuses and which directs the received signals as a beam of electro-magnetic radiation to the transducer of the receiver, the reflector having one or more eccentric apertures therein to interrupt portions of the signal, the reflector being rotated, in use, such that samples of attenuated signal strength may be taken when the interrupted portion is at different radial positions relative to the focused beam of electro-magnetic radiation.
Advantageously the reflector comprises two reflective plates one mou
REFERENCES:
patent: 3859658 (1975-01-01), Rabow
patent: 4010472 (1977-03-01), Mountcastle et al.
patent: 4156241 (1979-05-01), Mobley et al.
patent: 5089824 (1992-02-01), Uematsu et al.
Scott Brian C. L.
Scott David
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