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Satellite: New to Satellite
15 October 2009 - 10:05pm
Nearly every 2 or 3 degrees apart in the Sky over the Equator has a "Satellite" Slot. One slot can have up to 2000 channels. Satellites from about 20 "slots" can be received in Ireland.
Over 1400 TV and over 1200 Radio are available, legally and free, here in Ireland. (You do need a TV licence).
There are many "Providers" like Sky that for a subscription supply extra "Pay TV" or "Pay per view" channels.
Sky rent satellite capacity or transponders from SES-Astra and Eutelsat. Since Space is quite roomy up to 8 satellites can be hundreds of miles apart in a group or "constellation" and seem like a single satellite with many channels to a receiving dish on the ground. A modern Satellite may use about 200W per transmitter and have a 3kw Solar panel. This is modest compared with a terrestial TV transmitter of 1kW to 800kW.
Satellite TV comes from many different satellites about 22,500 miles above the Equator.
A satellite at 28E degrees is not at that compass bearing. In Prague it would be due south, as that city in Central Europe is approximately 28 degrees EAST of London, the "zero" or Greenwich Meridian, an imaginary line from North to South pole through London.
In 1948 Arthur C. Clarke propsed that if a satellite was at a particular height orbiting the Earth around the Equatorial plane it would seem stationary. The International Space Sation and Iridium satellites are in Low Earth orbit of a few hundred miles so they "whizz" overhead. The Moon is our largest Satellite and because it is far away it takes about 28 days to circle the Earth.
Nornal "Direct To Home" (DTH) Satellite TV uses frequencies of around 10750 to 12600MHz (10.5 to 12.6GHz). This is over 100 times the frequency of VHF FM radio, or 20 times UHF TV. DTH signals are Ku Band microwaves.
These signals can't be easily fed down a cable like signals from a TV aerial.
These signals reflect better on small metal mirrors. VHF and UHF TV would need huge mirrors to reflect them effeciently due to the lower frequency which means a 100 times longer wavelength.
A curved mirror acts like a lens to focus light or radio waves. So a parabolic shaped dish or "offset part" of a larger imaginary dish collects the signals and focuses them. The Satellite signal "radio" or "microwave" receiver is fitted here on an arm sticking out from the dish. This receiver is called a "Low Noise Block" or LNB. It converts the signal to a much lower frequency overlapping the UHF TV band, 750MHz to 2100MHz.
Usually vertical aerials pick up vertically polarised signals and horizontal rod aerials pick up horizontal signals. In theory we can transmit and receive two proigrams at the same time on the two polarizations. This is not done with normal radio and Tv as the reflections from hills. buildings and trees reverse or shift the polarization. But it does work from Satellite as there is nothing except a few clouds in between.
Created by: watty
15 October 2009 - 10:06pm
#1
Why you can't spilt the LNB signal to feed several Satellite receiver boxes, like Cable TV or an aerial.
The LNB is remotely switched between Horizonatal (H) and Vertical (V) (Nothing actually rotates, it is electronic). Also the cable between the LNB and the satellite receiver can't carry all the signals on H or V at once. Just Like TV is split into Band III VHF and BandIV/V UHF (and even "hyperband" cable TV), the Ku microwave band is split in two at 11.7GHz. The LNB will either receive 10.75 to 11.7GHz or 11.7Ghz to 12.6GHz. This "band" switch is accomplished usually by a 22kHz tone, off is low band and on is high band. Similary the H/V is 18V approx. for H and 14V approx for V. The 14 or 18V is also used to power the electronics in the LNB.
Thus the LNB can change to any of four states, as the user moves between channels without being aware that anything is happening. Adjacent channels on a satellite usually alternate H and V polarity as this gives better seperation of their signals at the receiver.
Because of the way the receiver controls the LNB any attempt to "split" the LNB cable fails if both satellite receivers are not receiving from the same polarity and same band.
Tuning
There is no tuning dial or bar or frequency display like normal TV tuners or analog Satellite. The TV or Radio is sent on a digital stream of data with many other channels. One such group at a single frequency is a Transponder (TP). The speed of the data is called the Symbol Rate (SR). A high SR may allow 8 TV sations and 10 Radio stations to share a TP (transponder), perhaps 27500k . A very slow stream may be 1500K and only support a single station.
In addition errors may occure in the informtion data stream. When this happens on a CD or DVD it my stop, skip or simply have a quiet / blank moment (scratch or dirt). So Satellite Digital transmission adds extra information to correct errors, This is called Forward Error Correction (FEC). 7/8 is the least amount and used by links with large dishes. 1/2 is the most amount of FEC and alows a very small dish. 2/3 and 5/6 are common.
So to "tune" you enter a frequency, Polarity and FEC and the Satellite receiver returns a list of possible channels you can add. Most non-Sky receivers can automatically work out the FEC, so you don't nned to enter it.
More expensive receivers for serious enthusists can do a "Blind Scan". This is somewhat slow but will find "unpublished" transponders and automatically calculate the SR and FEC. Useful for "hunting" transatlantic satellite news feeds.
Another option is that a particular "known" transponder will have a list of transponders. This is an option to use on some receivers called a "Network Transponder Search". The other transponders are automatically added. This works to add most transponders on Sky and also many at 13e and 42e.
15 October 2009 - 10:06pm
#2
Unlike Cable and MMDS, you own your Satellite receiver. Access to some channels and packages are by viewing card / encryption.
There are over 1000 free TV and radio to be received in Ireland
1) Types of Card / CAM / Encryption on Satellite:
Signals can be CLEAR = No card needed = FTA = Free To Air
FTV = Free To View= A card is needed, but it is free. The signal is encrypted to prevent those without a card watching. Only people in a particular area get a card, cards might vary with area. Sky3 C4, Five in UK using a "Freesat From Sky" card
A cancelled ROI subscription card now acts as FTV card for Sky3.
FTV Soft Encrypted = A correct viewing CAM neeeded, but no card. Some Scandinavian countries. The CAM is supplied for a nominal fee. Viewing is free.
PayTV= Card Needed, you pay an annual or monthly subscription
Sky Packages: Sky One, UK Gold, Discovery,
BBC Prime
Disney
AB Sat
PPV= pay per view = You need a card, and either pay each time by credit card or an account is debited each time you view. (Sky Box Office)
CAM = Conditional Access Module.
Each encryption system (there are many) usually needs a different CAM. The cam has a slot for a viewing card. Magic CAM and ALLCam are "patched" CAMS that can use more than one type of card.
A CAM can be built in or fit into a slot called a CI (Common Interface).
The Digibox can ONLY be used for Sky Pay TV and FTA. Its CAM is called "videoguard" and is built in. It has no enabled CI to take non-Sky CAMs.
Any other Digital Receiver can only do the FTA channels on SKY as Sky does not sell a "standalone CAM" for a CI slot.
No-one has a licence to make a Receiver with a Videoguard builtion and some other CAM like Viaccess.
BBC Prime uses a Viaccess CAM. So a receiver for BBC Prime (viewing card is about £85 Stg p.a.) can't get FTV or Pay TV from Sky, only FTA from Sky. You can get a receiver with Viaaccess built in (a slot for viewing card) with or without CI for other CAMs.
Other services use CAMs such as CONAX, Seca, Betacrypt etc.
You can get receivers with NO CAM built in and no CI slot. These will only receive FTA, not even FTV signals.
Currently Sky seem to be making it harder to use both a Pay TV card and a FTV Card in the same Digibox.
A UK address (mainland or NI) is required for a UK FTV card. It only works in Digibox.
A Dutch address is needed for a Dutch FTV card. It will NOT work in a Digibox. It will work in many boxes that have the correct CAM (Seca-2?), built in, or using a CI.
Many countries have FTV card Schemes.
Exceptions:
IRELAND: NO FTV. All Irish TV is ROI Sky Family Pack or Higher. Does not work on any UK package, nor on cheaper ROI Sky packs.
GERMANY, ITALY: Most of their TV is FTA. No card required. There are of course additional PAY TV channels. Very large number of German and about 8 mainstream Italian
POLAND: Some channels are FTA.
Spain: Mostly subscription.
France: Only FTA all main channels on Analog SECAM (Telecom Bird), otherwise TV5, TV5e, Arte and France5 (formerly La Cinqueme) are main FTA
Greece: Some FTA
Where are these packages / Channels?
Sky provide and install a system at a subsidy of almost 200 Euro on codition you have a phone line connected for the first year and subscribe for a minimum of a year.
Sky signals com from 28.2 E
All the TV satellites are in a "ring" around the equator about 22,500 miles out in space, so that they appear stationary to an observer (a Dish) on the ground.
With current dish sizes a "position" is roughly every 3 degrees, so there are roughly 180 "slots". Each slot is invisible to the next due to the focus of the dish, so each can use the same frequencies. The Digital Satellites need a "Unversal LNB" on the dish, this does two "bands". Many analog receivers on had an LNB for the lower "band". So each slot in Analog can have about 130 TV channels or in Digital about 1,300 TV channels. The space required for one TV channel can accomodate about 100 Radio channels.
Free BBC World TV, Italian, Polish and more than 20 other nations use the 13E Slot called Hotbirds.
Most of the German free TV is at the old Sky analog position or slot of 19.2E called Astra1
Each slot can have many satellites that "appear" as one satellite to your receiver. The Sky Digital Receiver actually picks up from two satellites at 28.2E, Eurobird owned by Eutelsat and one of the "Astra 2" fleet owned by SES-Astra. Sky only rents channels. Not all of the signals on your Digibox are actually even Sky rented channels.
