Relevant links on this web site:

European satellite ISPs

Satellite Internet - How it works

Satellite internet forum

VSAT index page

Introduction and explanation of VSATs

VSAT data capacity

Bentley Walker HX VSAT hub

BBI - SIT Broadband Internet - Satellite Interactive Terminal

This page provides an explanation of what the above abbreviations mean.

Direct access to the internet using direct two-way Broadband Internet ( BBI ) Satellite Interactive Terminal ( SIT ) is the future for all those people in areas where DSL, ADSL or cable modems are not possible.

Satellite Interactive Terminal ( SIT )

The Satellite Interactive Terminal ( SIT ) is simply a small satellite dish, similar to that for satellite TV but with a RF (Radio Frequency) module in front that both receives (LNB=Low Noise amplifier and Block down-converter)  and transmits (BUC=Block Up-Converter and high power amplifier). The quality of the dish is superior to that used for satellite TV since the terminal transmits and may thus cause unacceptable interference to other satellite service users.  Dish profile accuracy and feed horn dimensions are critical to the off-axis sidelobes and the construction of the ortho-mode transducer (OMT) and other feed parts and antenna geometry are critical to the cross-polarisation isolation, which matters a lot to keep interference to other services on the same satellite under control. The transmit modem and its BUC amplifier must not radiate spurious interference on the wrong frequencies.

Broadband Internet ( BBI )

The Broadband Internet ( BBI ) refers to the reception of a, typically, 27.5 Msym/sec carrier which provides for fast download of web pages, MP3 audio and video etc., combined with a low bit rate transmit capability to allow requests for web pages, mouse clicks, email messages etc to be sent into the internet. The long term average bit rates, per PC are about 20kbit/s download and 3 kbit/s upload.  A very few users consume many times this amount with file sharing and video/audio applications. Prices depend on your fair share and and such heavy traffic users must pay far more for their service.

The term BBI-SIT has never really caught on.  The term VSAT meaning Very Small Aperture Terminal is far more popular.  The marketing people don't like it however since it a term of long standing and associated with early larger VSATs, of 1.8m diameter or larger and needing to comply with complex planning rules and licencing.  Given the more modern smaller terminals a different name is thought helpful in minimising licencing and regulatory problems. The latest VSATs operate in Ka band and use type approved designs, and do not need individual licencing in some countries.

Page started 20 Nov 2003, last amended 15 Jun 2020