Parabolic antenna (TV)

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Parabolic antenna for receiving satellite broadcasts

A parabolic antenna for satellite broadcasting reception , often Satellite dish called, receives broadcast programs such as radio, television or other services such. As Internet access via satellite , from a broadcast satellite on a geostationary orbit is broadcast. Due to the great distance of about 36,000 km, the signals on earth are very weak. To receive them, in Central Europe z. B. for the Astra satellites in Ku-band parabolic antennas with a diameter of usually 85 cm (60 cm without bad weather reserve) required.

construction

Parabolic antenna and solar cells on a hut in East Timor

The antenna consists of the parabolic mirror and the receiving head with horn antenna , integrated frequency converter and IF amplifier ( Low Noise Block Converter , LNB). The parabolic mirror bundles the signal waves at its focal point through reflection . The receiving head, which processes the signals, is located there. Depending on the version, one or more coaxial cables transmit the received signals to a satellite broadcast receiver (receiver) or a distribution system ("satellite system").

The parabolic mirror

The size of a parabolic antenna is specified with the diameter of the parabolic mirror. The most common types of antennas have a diameter of 60 to 120 cm. The area and thus the received energy grows quadratically with the diameter because of the more precise focusing . For example, the reception area of ​​an 85 cm antenna is twice as large as that of a 60 cm antenna. Unlike the terrestrial transmission frequencies in the VHF or UHF band, the radiation in the Ku band is noticeably attenuated by moisture. The signal strength can decrease by more than 6 dB.

Offset antenna

The offset antenna (used almost exclusively today) is in principle part of a rotationally symmetrical parabolic mirror antenna. The mirror surface is no longer circular, but oval. In contrast to the rotationally symmetrical parabolic antenna, the offset antenna does not "look" directly at the satellite, but rather shows a considerable angular deviation (offset angle, usually 25 °). The LNB needs the same angular deviation in the other direction so that it is still in the focal point of the antenna mirror.

As an advantage of this antenna shape, the LNB no longer hangs in the beam entrance, so no received energy is lost. The reflector also has somewhat more favorable dimensions. Since the reflector of the offset antenna is more vertical than with a symmetrical parabolic antenna aligned in the same direction, snow and dirt do not collect in the reflector as easily.

Due to the offset angle (here called α) as the differential angle in comparison with a rotationally symmetrical parabolic antenna, the effective area of ​​the parabolic reflector is approximately cos (α) smaller, which is compensated for by the elliptical shape of the offset antenna.

material

Today, parabolic mirrors are mostly made of painted steel or aluminum. For this purpose, the manufacturers use lacquers or powder coatings. Adhesive foils and synthetic resin lacquers are unsuitable because they introduce additional attenuation in the reception path. The paint is always matt, otherwise the sunlight would be reflected in a concentrated manner onto the LNB when the sun is behind the satellite. Plastic mirrors are rarely used because of their higher price. They have a metal grille built into the plastic that reflects the radiation. In contrast to aluminum mirrors, the fastening screws do not go through the mirror surface, but the plastic goes from the mirror shape to a holder on the back. The plastic can be any color or it can be transparent, so that the antenna is hardly noticeable on facades. There are also wire mesh antennas. Their advantage is that they offer less (but not negligible) resistance to the wind, their disadvantage is the risk of rust if the paint is damaged. They are usually painted black to be inconspicuous.

The receiving head (LNB)

Mounted LNB

The receiving head is located in the focal point of the parabolic mirror. The Ku band (10.7 to 12.75 GHz) is used in Europe to receive satellite programs with relatively small antennas . The satellite signals are amplified by low noise block converters ( LNB , rarely also LNC ). This converts the signal into a frequency range of 950 to 2150 MHz, which can be received by a satellite receiver.

When satellite technology was introduced, LNBs were initially mainly produced, which covered the frequency range from 10.95 to 11.7 GHz, which was common at the time, on the max. 48 analog programs could be transmitted. Later the 10.7 to 10.95 GHz range was also used for satellite reception. The entire range from 10.7–11.7 GHz is now known as the low band. The first satellite to use frequencies between 10.9 and 10.95 GHz was the Astra 1C, and the first satellite to use frequencies between 10.7 and 10.9 GHz was the Astra 1D.

Over time, the number of programs grew and the whole Ku-band was used. The 'new' frequency range between 11.7 and 12.75 GHz is known as the high band. For this purpose, LNBs were developed that covered the entire frequency range. To differentiate, these are called universal LNBs . Mainly digital programs are broadcast on the high band. However, this is historical and has no technical background. Both analog and digital receivers can be connected to a universal LNB.

The switch from analog to digital television DVB-S , which began in 1996, was completed around 2002/2003; German programs alone were temporarily broadcast in analog form for the provision of basic services, but this was discontinued on April 30, 2012 .

Special designs

Torus antenna for receiving several satellite positions

Multifeed holder

It is usually common practice to aim parabolic antennas directly at the satellite. However, since neighboring satellites can also be received with one antenna, a multifeed holder ” is used to attach two (or more) LNBs to one antenna, with several LNBs firmly positioned in different focal points of the satellite antenna (one LNB per satellite). Since at least one LNB is not aligned with the focal point in this case, such antennas are also called "cross-eyed mirrors" . The torus antennas are a special case .

Rotatable antennas

If the use of several LNBs is too complex, an antenna mast with a motor and a polar mount bracket is used that, when rotated , moves along the celestial equator on which the geostationary satellites are located. However, such systems are only suitable for one participant. A rotating, stationary satellite antenna can cover approx. 30 different satellite positions with television programs with a clear view to the south in Central Europe. In this way, the theoretically usable bandwidth is multiplied to more than 100 GHz. Special antenna rotors are available from around 40 €, the installation requires some skill. Rotatable systems with a mirror size of 1 m currently receive more than 6,000 radio and television programs in Central Europe, almost half of which are freely receivable.

Control commands for multifeed and rotating systems are transmitted using DiSEqC commands.

"Invisible" antennas

Flat antenna (panel antenna), corresponds approximately to a 60 cm mirror

For aesthetic or legal reasons, it can make sense to hide a parabolic antenna. For example, normal antennas can be hidden under plastic tables on the balcony or in empty rain barrels in the garden, the plastic of which allows the microwaves to pass through.

There are also various special designs, for example as a chair in which the backrest serves as a parabolic antenna when nobody is sitting on it. Another well-known alternative design is the flat antenna ( panel antenna ). Such special designs are not suitable for multifeed holders, but motor solutions do exist in some cases.

cabling

A coaxial cable with F connectors is used to wire the parabolic antenna .

Multi-party satellite solution

Parabolic antennas on a house facade

While the decision in favor of a parabolic antenna can be made quickly in single-family houses, this is often difficult in apartment buildings. It is not uncommon for individual antennas to be attached to such objects only in special cases. In order to avoid the accumulation of individual antennas, as shown in the picture, various solutions for satellite broadcast reception systems (also referred to as "satellite systems") have been developed, which get by with a common antenna (see also Digital Satellite Equipment Control ):

Compulsory fees in Germany and Austria

In January 1991, the Federal Ministry of Post and Telecommunications stated that it was no longer necessary to register parabolic antennas for the reception of radio and television programs from telecommunications satellites as part of a fee-based individual license with the authorities. The installation and operation of parabolic mirrors was thus free of permits and fees.

In 1991, the Austrian Post and Telegraph Administration also issued a general authorization or approval for the reception of radio and television broadcasts via satellite.

Legal right of a tenant to a parabolic antenna

Germany

The landlord does not need to tolerate any exposed cables or antennas on the house facade. In addition, as the owner of the house, the landlord has an interest in a uniform and undamaged facade design, because that preserves the value of the house. The landlord has the right to decide on the basis of his or her right to decide where the satellite antenna is to be installed, provided the antenna is firmly installed with screws. Even if the rental agreement does not allow a parabolic antenna to be installed on the house facade, a tenant has a legal right to have one installed if he can demonstrate a particular interest in receiving additional channels that are not received via the existing offer including additional offers ( pay TV ) can be. This can apply to foreign tenants or journalists, for example.

The Federal Constitutional Court has (decision of March 31, 2013 1 BvR 1314/11)

"Confirms the principles to be observed in civil disputes about the installation of parabolic antennas by tenants. The civil courts have to make a case-by-case assessment, in which the owner's interests of the landlord in the - also optically - undiminished preservation of the house and the information interests of the tenant in the use of generally accessible sources of information are to be adjusted. The interest of foreign tenants in receiving radio programs from their home country, including the special situation of linguistic and cultural minorities, must also be taken into account. "

Austria

According to OGH GZ 5Ob199 / 03f, you do not have to be restricted to certain offers (e.g. cable television). However, there are certain restrictions for tenants with regard to the diameter and mounting of the parabolic antenna, but these do not affect the actual right to access a parabolic antenna with the desired service (satellite).

Since the external appearance of the house is changed, and general parts may also be used, the owner of the apartment and possible landlord needs the consent of the other owners. If the appearance is compromised, they don't have to put up with it. In problematic cases, court settlements may be reached in non-litigation proceedings.

literature

  • Bernhard Krieg: Satellite TV Little theory, a lot of practice. 1st edition, Elektor Verlag GmbH, Aachen 1987, ISBN 3-921608-47-3 .
  • Herbert Zwaraber: Practical setup and testing of antenna systems. 9th edition, Dr. Alfred Hüthig Verlag, Heidelberg, 1989, ISBN 3-7785-1807-0 .
  • Gregor Häberle, Heinz Häberle, Thomas Kleiber: Expertise in radio, television and radio electronics. 3rd edition, Verlag Europa-Lehrmittel, Haan-Gruiten 1996, ISBN 3-8085-3263-7 .

Web links

Commons : Satellite Dishes  - Collection of images, videos and audio files

Individual evidence

  1. Österreichisches Jahrbuch , Volume 63, Österreichischer Bundespressedienst, printing and publishing house of the Österr. Staatsdruckerei, 1992, p. 521
  2. BGH VIII ZR 118/04 (PDF; 23 kB)
  3. Prohibition of "satellite dishes" by the landlord only after carefully weighing up interests in individual cases . Press release No. 35/2013 of the Federal Constitutional Court of May 14, 2013.
  4. ^ Housing law for the owner ( Memento from February 21, 2013 in the Internet Archive ) (PDF; 1.4 MB), Tyrol Chamber of Labor