Revision as of 23:01, 2 August 2009 edit Read-write-services (talk \| contribs) Extended confirmed users 1,881 edits percent DDM/m = 0.145% ← Previous edit		Revision as of 15:12, 3 August 2009 edit undo Ojw (talk \| contribs) Extended confirmed users 3,296 edits where did these numbers come from? Next edit →
Line 1: '''Difference in the Depth of Modulation''' or '''DDM''' is a method used by the [[Instrument Landing System]] in conjunction with the associated airborne receiving equipment to define a position in airspace. DDM is usually expressed in percentage, however 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 metre {{citation needed}}. The two individual audio modulation frequencies and their associated sidebands are 150[[Hertz\|Hz]] 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 half-scale deflection.

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