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Difference in the depth of modulation
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<p>The difference in the depth of modulation (DDM) is used by <a href="/facts/Instrument_landing_system/CTLARvA8">instrument landing systems</a> 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. The two individual audio <a href="/facts/Modulation/aAXPjINv">modulation</a> frequencies and their associated sidebands are 90 and 150 <a href="/facts/Hertz/6Wshj5qm">Hz</a>. The DDM for a localizer at the outer extremity of the course sector is 15.5% or an electric current equivalent of 150 microamperes <a href="/facts/Full_scale_deflection/zul4DWDz">full scale deflection</a>. </p>