Space modulation
Encyclopedia
Space modulation is a radio Amplitude Modulation
technique used in Instrument Landing System
s that incorporates the use of multiple antennas fed with various radio frequency powers and phases to create different depths of modulation
within various volumes of three-dimensional
airspace. This modulation method differs from internal modulation methods inside most other radio transmitters in that the phases and powers of the two individual signals mix within airspace, rather than in a modulator.
An aircraft with an on-board ILS receiver within the capture area of an ILS, (glideslope and localiser range), will detect varying depths of modulation according to the aircraft's position within that airspace, providing accurate positional information about the progress to the threshold.
signals (90 Hz and 150 Hz), along the glidepath (GP) and the localiser (LLZ) trajectories into airspace
. It is this signal that is projected up from the runway which 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 the aircraft from the correct position for the aircraft to touchdown on the threshold. The difference between the two signal modulation depths is zero when the aircraft is on the correct glideslope on approach to the runway—i.e. No difference (zero DDM
), produces no deviation from the middle indication of the instrument's needle within the cockpit of the aircraft.
Amplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
technique used in Instrument Landing System
Instrument Landing System
An instrument landing system is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument...
s that incorporates the use of multiple antennas fed with various radio frequency powers and phases to create different depths of modulation
Difference in the Depth of Modulation
The difference in the depth of modulation or DDM is used by instrument landing systems in conjunction with the associated airborne receiving equipment to define a position in airspace. DDM is usually expressed in percentage but may also be expressed in microamperes...
within various volumes of three-dimensional
Three-dimensional space
Three-dimensional space is a geometric 3-parameters model of the physical universe in which we live. These three dimensions are commonly called length, width, and depth , although any three directions can be chosen, provided that they do not lie in the same plane.In physics and mathematics, a...
airspace. This modulation method differs from internal modulation methods inside most other radio transmitters in that the phases and powers of the two individual signals mix within airspace, rather than in a modulator.
An aircraft with an on-board ILS receiver within the capture area of an ILS, (glideslope and localiser range), will detect varying 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 and 330 MHz for the GP), to transmit two Amplitude ModulatedAmplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
signals (90 Hz and 150 Hz), along the glidepath (GP) and the localiser (LLZ) trajectories into airspace
Airspace
Airspace means the portion of the atmosphere controlled by a country above its territory, including its territorial waters or, more generally, any specific three-dimensional portion of the atmosphere....
. It is this signal that is projected up from the runway which 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 the aircraft from the correct position for the aircraft to touchdown on the threshold. The difference between the two signal modulation depths is zero when the aircraft is on the correct glideslope on approach to the runway—i.e. No difference (zero DDM
Difference in the Depth of Modulation
The difference in the depth of modulation or DDM is used by instrument landing systems in conjunction with the associated airborne receiving equipment to define a position in airspace. DDM is usually expressed in percentage but may also be expressed in microamperes...
), produces no deviation from the middle indication of the instrument's needle within the cockpit of the aircraft.