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Technical explanation of internet via satellite service

Skylinx VSAT terminal demonstration

Call in progress slot 2 to slot 3, 8kbit/s each way, 0.1 W/carrier,Eb/No=10 dB
Multiple voice and data carriers may be transmitted and received by a single VSAT terminal.

2.5 watt amplifier and 1.8m ETSI f/d=0.8 dish
The example site described comprises one indoor chassis box with 4 slots. These slots are occupied by three voice/data channel units and an RF up/down converter board.

The outdoor equipment comprises a 1.2m or 1.8m antenna and 2.5W ORU. The 1.8m antenna shown works fine but would look better if I cleaned it!. Operation is in the Eutelsat 7 deg East, D-SAT160, service, covering all of Europe and very much beyond.

Slot 1 (top slot)
The data channel unit in Slot 1 is configured for 16 kbit/s data and is used by Eutelsat for remote monitoring and control.

Slot 2
The voice/data/fax channel unit in Slot 2 is configured for 8 kbit/s voice calls using G729 voice coding.   Telephone calls may be made direct to channel units at other 1.2m or 1.8m terminals or to the PSTN.   For a PSTN voice call dial the full international phone number format starting 00.

Slot 3
The voice/data/fax channel unit in Slot 3 is configured for 64 kbit/s voice calls using PCM coding.   Dialling as per slot 2 above.   Using a computer modem plugged into the phone socket, dialup calls to the Internet are possible.

Slot 4 (lowest slot)
An RF up/down converter board is in Slot 4 and also supplies DC power to the ORU and LNB via two coax cables.


The channel units in slots 2 and 3 are multi-mode and will reconfigure on demand. If a call from Slot 2 is made to Slot 3, then Slot 3 will also transmit and receive 8 kbit/s voice. In the figure at the top of this page the two 8 kbit/s carriers are shown side by side while the call is in progress using the telephones shown. The transmit power was only 0.1 watt per carrier for an Eb/No=10 dB.

Alternatively if a call is made from slot 3 to slot 2 then 64 kbit/s is established both ways (0.8 watt per carrier).

These particular channel units have a maximum bit rate of 160 kbit/s - thus the service name D-SAT 160.   Channel units for up to 2 Mbit/s are available.

The network is a mesh DAMA and calls are made via the satellite direct to any other terminals in the network.   In the example, voice and data calls are made from this 1.8m terminal to a 1.8m hub terminal at Fucino in Italy ( internet satellitare ).   If Slot 3 is called from Slot 2 then the call is also from a 1.8m to a 1.8m terminal. When a call is made to a 1.2m terminal the power transmitted is increased accordingly.

Data only channel units are also available. These may be used for both 'instant' data call set up and for long term data circuits.  The data port might typically be connected to a router (or a PC).

Additional chassis boxes, with 4 more channel units per box, may be daisy chained to permit more carriers.   For example, a further chassis would permit a total of 7 voice/data channel units and allow several telephones or data equipments to be attached. One 64 kbit/s call is equivalent to eight simultaneous 8 kbit/s phone calls.

Last amended 27 Feb 2005, 3 May 2016