|Lecture 1, General Principles (http://www.satcom.co.uk/article.asp?article=3)|
|Welcome to the first lecture in the RPC Satcom Tutorial
At any point in the lecture, you can skip to a latter section, or back to earlier sections using the guide on the left.
The Pioneers of Satellite Communications
|-Konstantin Tsiolkovsky (1857 - 1935)
Russian visionary of space flight First described the multi-stage rocket as means of achieving orbit.
Link: The life of Konstantin Eduardovitch Tsiolkovsky
-Hermann Noordung (1892 - 1929)
-Arthur C. Clarke (1917 - )
|INTELSAT is the original "Inter-governmental Satellite
It once owned and operated most of the World's satellites used for international communications, and still maintains a substantial fleet of satellites.
INTELSAT is moving towards "privatisation", with increasing competition from commercial operators (e.g. PanAmSat, Loral Skynet, etc.).
INTELSAT has 143 members and signatories listed here.
|-Permanent General Secretariat opened September 1978
-Intergovernmental Conference adopted definitive statutes with 26 members on 14 May 1982
-Definitive organisation entered into force on 1 September 1985
-Currently almost 50 members
-Moving towards "privatisation"
Advantages & Disadvantages
|When, and when not, to use satellites|
|When to use satellites:
When to use terrestrial:
|Frequency Bands Allocated to the FSS|
|Frequency bands are allocated to different services at World
Radio-communication Conferences (WRCs). Allocations are set out in Article S5 of the ITU
It is important to note that (with a few exceptions) bands are generally allocated to more than one radio service
Bands have traditionally been divided into "commercial" and "government/military" bands, although this is not reflected in the Radio Regulations and is becoming less clear-cut as "commercial" operators move to utilise "government" bands.
|The Satellite Link|
Power density from transmit antenna at receive aperture is:
Power collected by receive antenna:
Path transmission loss ("free space loss"):
Thermal noise at output of receive antenna:
Hence "Link Budget Equation" expressed in dB:
When calculating the link budget, we must take account of additional factors:
Figure of merit (G/T) is a useful way of categorising the performance of a receiving system.
In a constant RF field, different receiving systems (with the same receive bandwidth) will yield a C/N proportional to the system G/T.
EIRP is the usual way of combining transmit power and gain:
So, the link budget equation is normally expressed as:
The satellite link:
Uplink and downlink are analysed seperately as individual radio links:
Overall Link Quality:
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