Satellite Dishes

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Principle of operation

The parabolic shape of a dish reflects the signal to the dish’s focal point. Mounted on brackets at the dish's focal point is a device called a feedhorn. This feedhorn is essentially the front-end of a waveguide that gathers the signals at or near the focal point and 'conducts' them to a low-noise block downconverter or LNB. The LNB converts the signals from electromagnetic or radio waves to electrical signals and shifts the signals from the downlinked C-band and/or Ku-band to the L-band range. Direct broadcast satellite dishes use an LNBF, which integrates the feedhorn with the LNB. (A new form of omnidirectional satellite antenna, which does not use a directed parabolic dish and can be used on a mobile platform such as a vehicle was announced by the University of Waterloo in 2004.

The theoretical gain (directive gain) of a dish increases as the frequency increases. The actual gain depends on many factors including surface finish, accuracy of shape, feedhorn matching.

With lower frequencies, C-band for example, dish designers have a wider choice of materials. The large size of dish required for lower frequencies led to the dishes being constructed from metal mesh on a metal framework. At higher frequencies, mesh type designs are rarer though some designs have used a solid dish with perforations.

A common misconception is that the LNBF (low-noise block/feedhorn), the device at the front of the dish, receives the signal directly from the atmosphere. For instance, one BBC News countdown shows a "red data stream" being received by the LNBF directly instead of being beamed to the dish, which because of its parabolic shape will collect the signal into a smaller area and deliver it to the LNBF.


Modern dishes intended for home television use are generally 43 cm (18 in) to 80 cm (31 in) in diameter, and are fixed in one position, for Ku-band reception from one orbital position. Prior to the existence of direct broadcast satellite services, home users would generally have a motorised C-band satellite dish of up to 3 metres in diameter for reception of channels from different satellites. Overly small dishes can still cause problems, however, including rain fade and interference from adjacent satellites.

Different kinds of Satellite Dishes

a) Offset Antenna
b) Prime Focus Antenna
c) Flat Antenna
d) Cassegrin Antenna
e) Multi Focus Antenna

Offset Antennas

These antennas represent just a part of a parabolic or prime focus antenna. Their focus is not in the geometrical centre of the dish but a bit lower. Since the LNB doesn’t stand in the way of the signal these antennas can be smaller than others.

Prime Focus Antenna

Prime focus antennas have a parabolic shape and characteristic is that the focus is in front of the centre of the parabola in the geometrical centre that is. That means if the LNB is attached to this antenna it can be found above the middle of the antenna and so the LNB blocks a part of the emitted signals and therefore these antennas have to be bigger than offset antennas. Offset antennas replaced these antennas nearly completely. Today they are mostly used for the reception of signals in the C belt, since these are the only antennas that are built in scopes up to 10m.

Cassegrin Antennas

These antenna with two reflectors receive signals better. It looks like an offset antenna with the exception that in the place where the offset antenna has a LNB attached the cassegrin antenna has an additional reflector, which has the task to reflect signals coming from the main reflector onto the LNB, which is placed on the LNB-carrier in front of the small reflector. This means the signals are reflected twice before they get to the LNB.

Gregorian Dish

A subversion of satellite antenna that uses a concave hyperbolic
reflector that points signals to the converter and that is placed
opposite of the main reflector.

Flat Antennas

This antenna is made of many units, which receive signals, afterwards this received signals are united and directed to the LNB. Technically speaking this antenna collects electromagnetic waves. Since this antenna receives through several units it receives a stronger signal. This antenna can be smaller than advised for several areas.

Multi Focus Antennas

These antennas are made not long ago. They are offset antennas, which have a specially built reflector, which reflects received signals from surrounding satellites to one focus. You can recognize such an antenna easily, since it quadratic and it’s longer than wider.

Source : Net, Wikipedia

[challenger View Profile Find User's Posts Find User's Threads PM User E-Mail User]

Good wook, Anish.
Can some one guide me to make a 12' dish? I'm looking for the calculation etc...

[fancier View Profile Find User's Posts Find User's Threads PM User E-Mail User]

don't try to make dish............. it will not work as u are thinking of................

[ajaysino View Profile Find User's Posts Find User's Threads PM User E-Mail User]

can u put the pictures also of these dishes. it will help to understand for the new users

[rena42war View Profile Find User's Posts Find User's Threads PM User E-Mail User]

hey friends if weather is not as favorable as usual then what can we do for boosting signals?

[surendermehta View Profile Find User's Posts Find User's Threads PM User E-Mail User]

(03-12-2011 12:22 PM)rena42war Wrote: Guests cannot see links in the messages. Please register to forum by clicking here to see links.hey friends if weather is not as favorable as usual then what can we do for boosting signals?

we can't boost signals, but with big size dish can recieve better. As size of a dish increases signal strgth also increases.

[sgnair View Profile Find User's Posts Find User's Threads PM User E-Mail User]

Dear admin,
I am a C band dish user. Now My dish have 2 LNBs. The first one is positioned towards 83 degree east to get Asianet Middle east and other FTA malayalam channels. The other one (a'm not correct) is twrds 93.5 East to get DD channels.
Keeping my 1st LNB in current position shall i change my 2nd LNB to different positions(like 88,78.5,122 East) in order to grab FTA more channels.
Expecting a good reply.
And pls tell me how can i adjust the LNB. now the 2nd LNB is screwed with the first one.

[jenius-jatt View Profile Find User's Posts Find User's Threads PM User E-Mail User]

@sgnair
Keeping my 1st LNB in current position shall i change my 2nd LNB to different positions(like 88,78.5,122 East) in order to grab FTA more channels.
Expecting a good reply.
And pls tell me how can i adjust the LNB. now the 2nd LNB is screwed with the first one.
__________
Dear sgnair,
You must post your SS of your dish setup for brtter reference.
Secondly you can visit the Related threads,Their are many thread which show the
83* as prime or Thaicom5 as prime and other LNB's for FTA channels.one of the
Link of 83* is as bellow:-
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[thuggle View Profile Find User's Posts Find User's Threads PM User E-Mail User]

please i have a big problem, I've newly bought strong 4669xii with 60cm and 90cm dish i want to use the 60cm for astra 2b and the 90cm for w4 w7. But ma prob here is im a newbie here and i dont know how to go about the installation . Please can someone help me with how to install the 2 dishes and the tp to use and how to input them. Please i do need your help. Thankyou i!m awaiting reply

or please is there any other satellite with interesting channels apart from eutelsat please let me know..... fta
please im in takoradi western part of Ghana

[sanuam View Profile Find User's Posts Find User's Threads PM User E-Mail User]

Satellite Dishes for gain

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