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- 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. Instrument landing system ground stations provide radio frequency signals that vary linearly in the depth of modulation from the centre or course line at a rate of 0.145% per meter. The two individual audio modulation frequencies and their associated sidebands are 150Hz and 90Hz. The DDM for a localizer at the outer extremity of the course sector is 15.5% or an electric current equivalent of 150 microamperes full scale deflection. (en)
- 調變深度差（英文：Difference in the depth of modulation，縮寫：DDM），即信號強度的差值，為儀器著陸系統使用之技術。在儀器著陸系統導引時，會發出重疊的調變信號，系統比較不同頻率的信號強度差，來判定是否在水平與垂直的中心線上。 例：
* ILS定位圖解 ILS定位圖解，上圖中飛機由左至右進入跑道，以飛機視點看，90Hz為偏左之波束(藍虛線)，150Hz為偏右之波束(紅虛線)，因此在飛機偏向中心線的左側時，90Hz 的信號強度會比 150Hz 來得強。而在中心線上時，兩頻率強度一致。 (zh)
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- 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. Instrument landing system ground stations provide radio frequency signals that vary linearly in the depth of modulation from the centre or course line at a rate of 0.145% per meter. The two individual audio modulation frequencies and their associated sidebands are 150Hz and 90Hz. The DDM for a localizer at the outer extremity of the course sector is 15.5% or an electric current equivalent of 150 microamperes full scale deflection. (en)
- 調變深度差（英文：Difference in the depth of modulation，縮寫：DDM），即信號強度的差值，為儀器著陸系統使用之技術。在儀器著陸系統導引時，會發出重疊的調變信號，系統比較不同頻率的信號強度差，來判定是否在水平與垂直的中心線上。 例：
* ILS定位圖解 ILS定位圖解，上圖中飛機由左至右進入跑道，以飛機視點看，90Hz為偏左之波束(藍虛線)，150Hz為偏右之波束(紅虛線)，因此在飛機偏向中心線的左側時，90Hz 的信號強度會比 150Hz 來得強。而在中心線上時，兩頻率強度一致。 (zh)
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- Difference in the depth of modulation (en)
- 調變深度差 (zh)
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