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Swivel Antenna

Probably many people know that television satellites are in a geostationary orbit, which is a circular orbit located above the Earth’s equator (0 latitude), on which, an artificial satellite rotates around the planet with an angular velocity equal to the angular velocity of the Earth’s rotation around its axis, and constantly dwells on the same point on the earth’s surface. The satellites are located on the so-called polar arc (photo 1) at an altitude of approximately 36,900 km above sea level, the satellite’s altitude is not chosen randomly, but based on calculations of centrifugal force so that the satellite does not fall to the ground and does not fly into open space. So, a rotary antenna is a motorized antenna, designed in such a way that when moving it describes exactly the same arc as the one on which the satellites in space are located. Due to the Earth’s gravitational force and the centrifugal force that counteracts it, the satellites are stationary relative to the earth’s surface, so it’s enough to install a device (motor) to move the antenna along the given satellite positions. There are two main types of motors – actuator and suspension. Many fans of satellite television do not stop receiving one or two satellites, but sometimes our capabilities are limited and we cannot afford to connect several antennas, especially if the installation is done outside the window. In this case, you can install a rotary antenna. So what is this antenna? Before answering this question, I would like to talk a little about such an invisible component of satellite television as a satellite. Actuator – a device that is an electric motor operating on a direct voltage of 36 volts. Rotating through the worm mechanism, it produces translational movements back and forth, causing the antenna to rotate. Actuators are mounted on the so-called polar suspension of the antenna. As a rule, these are antennas, starting from a diameter of 1.2m or more. In addition to the actuator, a positioner is also installed, on which the power and control functions of the actuator are assigned. A motor suspension is a device in which the polar suspension and the electric drive are connected together. This allows them to be installed on azimuthal antennas. But, unfortunately, there are limitations in the diameter of the antennas. Usually, motor suspensions work correctly with antennas not exceeding 1.3m. The power supply of the motor suspension does not come from the positioner, but from the satellite receiver via a television cable with a DC voltage of 13-18V. More details about the operation of these devices can be found in the article Motor suspension or actuator. In addition to installing the motor, it is also necessary to fine tune the antenna and fix the satellites. Two main stages can be distinguished – tuning the polar axis of the antenna and setting the exact positions of the satellites while storing them at the position of the auto-suspension or in the receiver menu. The polar axis begins to adjust from zero. As a rule, this is the topmost satellite. In Moscow and the region such is the Eutelsat W4 36 degrees east longitude. So, once having tuned the antenna, you can control it already from the receiver or positioner remote control, depending on the type of motor you have chosen and the positioner model. I would also like to make a small emphasis on the function of the disceks (DiSEqC) of positioners and satellite receivers. For the convenience of users, a system of disek 1.2 was developed, which allows you to automatically move the antenna when switching channels from one satellite to another. The system works according to the following principle: when you select a channel on a satellite receiver, it gives a command to the motor suspension or positioner to move to the desired satellite. Today, all modern receivers support this feature. As for the positioners, there are positioners with both the function of disks, and manual – controlled from the remote control. Back to our companions. No matter how great the capabilities of a system with a rotary antenna are, it will still not be able to catch all the satellites in the world, since some of the satellites remain on the other side of the Earth, beyond the horizon. In Moscow and the Moscow Region, reception of satellites is possible starting from 30 degrees west longitude and 105 degrees east longitude. There are some features of receiving satellites on antennas with a motor suspension and an actuator. In a system with a motor suspension, the turning angle will be larger; the motor suspension can move the antenna 180 degrees. A standard system with an actuator allows for an antenna turn of the order of 100 degrees depending on the parameters and antenna manufacturer. This is usually not critical, since in most cases, receiving extreme satellites is still not possible due to tall buildings or trees that are in the signal path. In addition to the Earth’s gravitational forces, the satellites are also affected by the gravitational forces of the moon and the sun, which leads to their displacement from a given orbit. This in turn causes satellites to drift relative to the signal receiving point on the earth’s surface.

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