Occupied vs Necessary bandwidth
With the ARRL bandwidth petition, the terms "occupied" and "necessary"
bandwidth have come to light. Our comments to the FCC will be taken more
seriously if we leave the impression that we know what we are talking about.
Specifically, we should know exactly what is meant by the terms "occupied"
and "necessary" bandwidth.
The current set of definitions of the spectral properties of transmitter
emissions,"necessary bandwidth," " occupied bandwidth," plus "out-of-band
emission," " spurious emission," etc. contained in Article 1, Section VI, of
the Radio Regulations came into being through the work of the World
Administrative Radio Conference in Geneva, 1979.
"Necessary bandwidth" is the width of the frequency band which is just
sufficient to ensure the transmission of information at the rate and with
the quality required under specified conditions for a given class of
emission.
"Occupied bandwidth" is the width of a frequency band such that, below the
lower and above the upper frequency limits, the mean powers emitted are each
equal to 0.5% of the emitted power. This is also known as the 99% emission
bandwidth.
For further information, view the following websites:
Terminology: channel bandwidth is defined in conjunction with the terms
occupied bandwidth and necessary bandwidth that are defined by ITU Radio
Regulations S1.153 (occupied bandwidth) and S1.152 (necessary bandwidth), as
follows:
"Occupied bandwidth: The width of a frequency band such that, below the
lower and above the upper frequency limits, the mean powers emitted are each
equal to a specified percentage B /2 of the total mean power of a given
emission. Unless otherwise specified by the CCIR for the appropriate class
of emission, the value of B /2 should be taken as 0.5%.
"Note 1: The percentage of the total power outside the occupied bandwidth is
represented by B.
"Note 2: In some cases, e.g., multichannel frequency-division multiplexing
systems, use of the 0.5% limits may lead to certain difficulties in the
practical application of the definition of occupied and necessary bandwidth;
in such cases, a different percentage may prove useful.
"Necessary bandwidth: For a given class of emission, the width of the
frequency band which is just sufficient to ensure the transmission of
information at the rate and with the quality required under specified
conditions."
grouper.ieee.org/groups/802/20/Contribs/C802.20-04-11r1c.doc (copy &
paste into your browser, then download the Word document)
"Necessary bandwidth: For a given class of emission, the minimum value of
the occupied bandwidth sufficient to ensure the transmission of information
at the rate and with the quality required for the system employed, under
specified conditions. Emissions useful for the good functioning of the
receiving equipment as, for example, the emission corresponding to the
carrier systems, shall be included in the necessary bandwidth."
http://wireless.fcc.gov/services/ind&bus/licensing/bandwidth.html
"Occupied bandwidth:
"1. The width of a frequency band such that, below the lower and above the
upper frequency limits, the mean powers emitted are each equal to a
specified percentage B /2 of the total mean power of a given emission.
Unless otherwise specified by the CCIR for the appropriate class of
emission, the value of B /2 should be taken as 0.5%. [NTIA] [RR] Note 1: The
percentage of the total power outside the occupied bandwidth is represented
by B. Note 2: In some cases, e.g., multichannel frequency-division
multiplexing systems, use of the 0.5% limits may lead to certain
difficulties in the practical application of the definition of occupied and
necessary bandwidth; in such cases, a different percentage may prove useful.
"2. The frequency bandwidth such that, below its lower and above its upper
frequency limits, the mean powers radiated are each equal to 0.5% of the
total mean power radiated by a given emission. [47CFR]"
http://www.atis.org/tg2k/_occupied_bandwidth.html
Check out some of these sites at:
http://www.google.com/search?q=necessary+bandwidth,+occupied+bandwidth,+necessary+bandwidth&hl=en&lr=lang_en|lang_fr&client=firefox-a&rls=org.mozilla:en-US:official&start=0&sa=N
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