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Product Guides > Oyster Internet - How and why it works

Mon, Feb 11th 2013

Oyster Internet - How And Why It Works

Satellite Internet works in a similar way to satellite TV in that it receives information from a geostationary satellite positioned on the geostationary belt around 40,000 km above the Equator. Satellite dishes for either TV or Internet need to be pointed to within 1° degree accuracy in order to receive good quality signals. A 1° difference on Earth equates to a 400 mile difference at 40,000 km into space.

The main technical difference between Mobile Satellite Internet and TV is the transmit functionality or Tx. Sat TV only receives data (Rx) while sat Internet both receives and transmits data (TxRx). It is for this reason that the skew angle is very sensitive when connecting to the Internet.

Skew Angle
When a satellite beam is sent it leaves the satellite in either a Vertical or Horizontal polarisation in relation to the Earth at its meridian. As the Earth’s surface is curved; when that beam reaches the earth’s surface this orientation is different and therefore requires adjustment. This angle of adjustment is called the Skew angle.

TV satellites transmitting their signal to the earth have a large footprint. As long as you are in that footprint, it is a relatively easy task to aim towards the satellite and acquire the signal. Transmitting a signal back is a much more precise task. If the antenna is not pointed or aligned correctly, it could cause interference by firing a high frequency transmission to an adjacent satellite. This Adjacent Satellite Interference (ASI) will potentially disrupt service to thousands of its users.

Satellite Internet is very sensitive to skew angle in different locations. Over the European wide footprint there can be a difference in skew angle of up to 50°. And through experimentation we have found there is total signal loss from a skew angle being out by as little as two degrees. By comparison the skew angle for TV reception will work within a 12° window and only really becomes critical when on the edge of the footprint. When the Astra2Connect system first connects to the satellite it goes through a handshake procedure, which checks that the iLNB is transmitting correctly. If anything is awry the handshake will not complete and the system will not connect. This is designed to prevent ASI and generally protect users on other satellite networks.

If using a manual satellite dish the skew adjustment is just part of the dish pointing operation. However when using a fully automatic satellite dish system like the Oyster Internet, it is very important to have an automatic skew adjustment as well – otherwise the dish will point automatically, but the internet would not connect without skew adjustment. In short – when looking at automatic Internet systems only consider ones with automatic skew adjustment.

Footprints
Astra2Connect provides its Internet service from the Astra 3 satellite @ 23.5° satellite. The Internet system requires both uplink and downlink beams (RxTx) to work, the footprints published on lyngsat and other sat TV websites are TV Receive Only (TVRO) and not correct for internet. The uplink footprint is smaller as it is based on both the size of the transmitter within the iLNB and the dish size.

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