A satellite dish is a type of antenna that receives or transmits electromagnetic signals to and from another location typically a satellite. A satellite dish is a type of microwave antenna. Satellite dishes come in varying sizes and designs, and are commonly used to receive satellite television. Many of the offset type of satellite dishes are sections of a larger parabolic dish.
Types of Satellite Dish Antenna
There are a number of dish antenna types. The first and simplest is the Prime Feed Focus Dish, which is a Parabolic Dish Antenna and the second is Offset Dish Antenna. One of the important technologies and equipment used in transmitting and receiving audio and video signals. Satellite dishes come in different models and sizes. People can also categorize the equipment based on its special uses. To know more about this equipment, it is best to have knowledge or backgrounds on the various kinds of satellite dishes.Details are given below:
- Parabolic Dish Antenna
A parabolic antenna is a high-gain reflector antenna used for radio, television and data communications, and also for radiolocation (radar), on the UHF and SHF parts of the electromagnetic spectrum. The relatively short wavelength of electromagnetic (radio) energy at these frequencies allows reasonably sized reflectors to exhibit the very desirable highly directional response for both receiving and transmitting. With the advent of TVRO and DBS satellite television, the parabolic antenna became a ubiquitous feature of urban, suburban, and even rural, landscapes. Extensive terrestrial microwave links, such as those between cellophane base stations, and wireless WAN/LAN applications have also proliferated this antenna type. Earlier applications included ground-based and airborne radar and radio astronomy. The largest “dish” antenna in the world is the Arecibo Observatory’s radio telescope at Arecibo, Puerto Rico, but, for beam-steering reasons, it is actually a spherical, rather than parabolic, reflector.
A typical parabolic antenna consists of a parabolic reflector illuminated by a small feed antenna.The reflector is a metallic surface formed into a paraboloid of revolution and (usually) truncated in a circular rim that forms the diameter of the antenna. This paraboloid possesses a distinct focal point by virtue of having the reflective property of parabolas in that a point light source at this focus produces a parallel light beam aligned with the axis of revolution.The feed antenna is placed at the reflector focus. This antenna is typically a low-gain type such as a half-wave dipole or a small waveguide horn. In more complex designs, such as the Cassegrain antenna, a sub-reflector is used to direct the energy into the parabolic reflector from a feed antenna located away from the primary focal point. The feed antenna is connected to the associated radio-frequency (RF) transmitting or receiving equipment by means of a coaxial cable transmission line or hollow waveguide. Practical considerations of antenna effective area and sidelobe suppression reduce the actual gain obtained to between 35 and 55 percent of this theoretical value. For theoretical considerations of mutual interference (at frequencies between 2 and c. 30 GHz – typically in the Fixed Satellite Service) where specific antenna performance has not been defined, a reference antenna based on Recommendation ITU-R S.465 is used to calculate the interference, which will include the likely sidelobes for off-axis effects.
- Offset Dish Antenna
The Offset Dish Antenna, has its LNB not mounted centrally, but to the side of the dish. Because the LNB no longer obstructs the signal path, the dish has a better performance than the Prime Feed Focus dish. This allows the dish diameter to be smaller. Another advantage of this type of dish is that it can be positioned almost vertically, whereas the Prime Feed Focus dish needs to be positioned more obliquely. The problem that it could collect rain and snow and give disturbance to the signals is therefore less likely to happen.
The Dual Offset Dish Antenna is an improvement on the Offset Dish antenna and has an even better performance. Its efficiency is about 80%. The main feature of this antenna is that it has two dishes: a larger receiving dish and a smaller dish facing the opposite direction which collects the signals from the larger dish and directs it to the LNB.
The Flat Antenna is the most compact type and visually the least obtrusive. This type is best suited for receiving signals from DTH satellites in central footprint areas. The LNB is built-in.
- TVRO (BUD)
A C-band dish (often abbreviated to BUD, for “big ugly dish”) is a colloquial name for a TVRO satellite dish used to receive satellite television signals from FSS-type satellites on the microwave C band. BUDs are usually 6½ to 12 feet or two to 3.5 meters in diameter, and have been a source of much consternation (even local zoning disputes) due to their reputation as an eyesore. BUDs were originally marketed in the late 1970s, with the earliest dishes being made of solid fiberglass and later models being made of wire mesh and solid steel or aluminum. BUD systems of the time came at a high cost, usually several thousand dollars. They work by receiving a low-power C-Band (~5GHz) frequency-modulated analogue television signal directly from the original distribution satellite — the same signal received by cable-company headends. Because analogue channels took up an entire transponder on the satellite, and each satellite had a fixed number of transponders, dishes were usually equipped with a polar mount and actuator to sweep the dish across the horizon to receive channels from multiple satellites. Switching between horizontal and vertical polarization was accomplished by a small electric servo motor which moved a probe inside the feedhorn throat at the command of the receiver (commonly called a “polarotor” setup). Higher-end receivers did this transparently, switching polarization and moving the dish automatically as the user changed channels.
BUDs were most popular in rural areas, beyond the broadcast range of most local TV stations. The mountainous terrain of West Virginia, for example, makes reception of over-the-air television broadcasts (especially in the higher UHF frequencies) very difficult. From the 1970s to the early 1990s DTH systems weren’t available, and cable TV systems of the time only carried a few channels, resulting in a boom in sales of BUDs in the area, which led to the systems being termed the “West Virginia state flower”. The term was regional, known mostly to those living in West Virginia and surrounding areas. Support for BUDs dried up when strong encryption was introduced around 1994. Many long-disconnected BUDs still occupy their original spot. Due to the number of systems in existence, their lack of usefulness, and because many people consider them an eyesore, used BUDs can be purchased for very little money.
Dish Antenna Sizes
Dish antennae come in various sizes, each with their specific characteristics and purposes. The size of the dish required depends upon whether you live in a central footprint area or in an outlying area. There are three sizes: small – 60 to 70 cm diameter, medium – 90 cm and large – 1.20 to 1.50 meters. There are also smaller sized dishes, with a 45 cm diameter, but these are specifically designed for DTH satellites, which because of their high transmission power permit smaller dish antennae.
Small-sized dish – 60 to 70 cm
o Wide opening angle (comparable with wide angle lens) and therefore quite easy to install and tune.
o Not very selective, with possibility of interference if the number of satellites is increased.
o Not very sensitive, but sufficiently sensitive to receive MPS satellites in central receiving areas.
o Thanks to its small size, it can be mounted almost anywhere, such as on a balcony.
o A relatively cheap alternative for satellite reception. For a reasonable price a complete installation including a dish antenna, LNC and satellite tuner can be purchased.
Medium-sized dish – 90 cm
o Acceptable, practical intermediate size between large and small dishes.
o Capable of receiving from many satellites.
o Rotor required.
o Stations which are more difficult to receive do not come through so well.
o The price is between the prices of the small and the large dishes. By purchasing a good quality LNC and a good satellite tuner, the various stations can be received at remarkably good quality.
Larger dish – 8ft. to 16ft.
o Small opening angle (comparable with a telephoto lens) and therefore must be installed and tuned by an expert.
o Very selective, and therefore little chance of interference.
o Only effective with a rotor.
o Much more sensitive than the small dish (hence better quality). Is also suitable to receive satellites which orbit further below the horizon and therefore transmit weaker signals.
o Wind resisting construction required due to the size.
o A large dish with a corresponding high quality LNB and a good satellite tuner will cost considerably more than a small dish.
Dish Antenna need for Private Use
A small dish can only be used to receive satellites in orbit not too far away from the south line. Outside that line the distance to the satellites soon gets much bigger and consequently the reception quality worsens. For this reason small dishes are always fixed and are only tuned once. A larger solid or mesh dish antenna has a larger focus which can be aimed much more accurately at a cluster of satellites that orbit closely together, and therefore is more selective than a small dish. Consequently, a large dish will be less troubled than a small antenna by interference problems of the various signals. On the other hand, a mini-dish is comparatively cheap and can always be replaced by a larger dish (and another LNB). Such a small dish can be installed easily, if need be on a windowsill, and is less sensitive to various influences, such as weather conditions.
As of 2018, there are many satellites over India. Most of the satellite channels have converted to digital so need an upgrade to be received and many are large networks, ethnic, and religious. Satellite@Internet India provides satellite data for people who want to receive premium FTA channels on a C-band mesh or solid dish. The dishes themselves can be modified to receive free-to-air C or Ku band signal. The stock LNBs fitted to typical C-band dish will usually need to be replaced with one of a lower noise temperature to receive digital broadcasts. With a suitable replacement LNB (provided there is no warping of the reflector) a C-band big dish can be used to receive free-to-air (FTA) signals. Several companies market LNBs, LNBFs, and adaptor collars for big-dish systems. For receiving FTA signals the replacement should capable of dual C/Ku reception with linear polarization, for DTH it will need a high band Ku LNBF using circular polarization. Older mesh dishes with perforations larger than 5mm are inefficient at Ku frequencies, because the smaller wavelengths will pass through them. Solid fiberglass dishes usually contain metal mesh with large-diameter perforations as a reflector and are usually unsuitable for anything other than C band.
Dish Antenna need for Cable Operators/ MSOs Use
Larger solid or mesh dishes have higher antenna gain, which can be an advantage when used with Cable Operator or MSOs, virtually eliminating rain fade. BUDs are most popular in Cable TV sector, beyond the broadcast range of most local TV stations.
The new 7th Generation Modern large parabolic antennas similar to BUDs are still in production by Indian Dish manufacture companies. New dishes differ in their construction and materials. The new 7th Generation, 12′, 16′ or 24′ ft. dish antennas are arriving in recently. The Improvements are:
- Larger Arm
- Stronger Collar
- Thicker gauge steel
- All around nut welds
- Pre-drilled holes for the feed arms to allow fine adjustments and peaking.
New mesh dishes have much excellent perforations and solid dishes are now made with steel instead of fiberglass. New systems usually include a universal LNB that is switched electronically between horizontal and vertical polarization, obviating the need for a failure-prone polar rotor. As a complete system they have a much lower noise temperature than old BUDs, and are generally better for digital Ku reception.