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Space modulation
From Wikipedia, the free encyclopedia
Space modulation is a radio Amplitude Modulationtechnique used
in Instrument Landing Systems that
incorporates the use of multiple antennas fed with variousradio
frequency powers and phases to create different depthsof modulation
within various volumes of three-dimensionalairspace. This
modulation method differs from internalmodulation methods inside
most other radio transmitters inthat the phases and powers of the
two individual signals mixwithin airspace, rather than in a
modulator.
An aircraft with an on-board ILS receiver within the capturearea
of an ILS, (glideslope and localiser range), will detectvarying
depths of modulation according to the aircraft's position within
that airspace, providing
accurate positional information about the progress to the
threshold.
Method used to determine aircraft position
The ILS uses two radio frequencies, one for each ground station
(about 110 MHz for LLZ and330 MHz for the GP), to transmit two
Amplitude Modulated signals (90 Hz and 150 Hz), along theglidepath
(GP) and the localiser (LLZ) trajectories into airspace. it is this
signal projected up fromthe runway that an aircraft using an
instrument approach, uses to land.
The modulation depth of each 90 Hz and 150 Hz signal changes
according to the deviation of theaircraft from the correct position
for the aircraft to touchdown on the threshold. The
differencebetween the two signal modulation depths is zero when the
aircraft is on the correct glideslope onapproach to the runwayi.e.
No difference (zero DDM), produces no deviation from the
middleindication of the instrument's needle within the cockpit of
the aircraft.
See also
Difference in the Depth of Modulation Instrument Landing
System
Retrieved from
"http://en.wikipedia.org/wiki/Space_modulation"Categories: Aircraft
stubs | Radio navigation
This page was last modified on 17 May 2009 at 22:53. Text is
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Modulation techniques
Analog modulation
AM SSB QAM FM PM SM
Digital modulation
FSK ASK OOK PSK QAMMSK CPM PPM TCM OFDM
Spread spectrum
CSS DSSS FHSS THSS
See also: Demodulation, modem
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encyclopedia
12/11/2009http://en.wikipedia.org/wiki/Space_modulation
