On Tuesday, December 29, 1998 10:49 AM, Chris Metz [SMTP:[email protected]]
wrote:
> > I suppose I am asking how does one convert MHz and GHz into
conventional
> bandwidth (bps) terminology. This for clearing this up for me and my
> apologies for the "simpleton" question.
>
>
Chris-
Your best bet is a good introductory text to digital communications either
at a good bookstore or local university bookstore. Satellite
communciations like many other communication systems employs modulation.
Simply put, the digital data (bps) is modulated onto a carrier frequency.
In the satellite world, this is typically done in the baseband to an
intermediate frequency (IF) such as 70 or 140 MHz and again
upconverted/downconverted to the RF carrier band. It's this RF band that
is referred to by the 4/6 GHZ and 12/14 GHz in your message. The satellite
equipment and associated baseband equipment can be collectively thought of
as a modem in terms of the downstream communications devices such as
routers, servers, etc. Besides the modulation, there are also the coding
techniques which alter the desired information bps, but this can be
compared to any other type of communications coding.
Example: information rate 512 kbps
FEC coding rate 1/2 -------> 1024 kbps
BPSK modulation --------> 1024 ksps (symbols)
(or QPSK mod) --------> 512 ksps
therefore, this carrier would occupy 1024 kHz (+ rolloff) of bandwidth
(or 512 kHz, QPSK case) and then be converted to it's assigned center
frequency
in the RF band
Typical Satellite Config: 500 MHz wide spread over several tranponders
Typical transponder bw: 27 MHz, 36 MHz, 54MHz, ....
Receive carriers centered between 14.0-14.5 GHz
Transmit carriers centered between 11.7-12.2 GHz
Hope this helps initially, but as I mentioned, you probably want to acquire
a basic text on digital communication systems. Most of them address
satellite as well.
Heidi E. Anderson Enterprise Rent-A-Car
WAN Engineering 600 Corporate Park Drive
01.314.512.2057 Clayton, MO 63105 USA
01.314.512.4057 FAX
[email protected]
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