The difference in the depth of modulation (DDM) is used by instrument landing systems in conjunction with the associated airborne receiving equipment to define a position in airspace.
[citation needed] The two individual audio modulation frequencies and their associated sidebands are 90 and 150 Hz.
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.
A modulation depth comparison navigational aid (MDCNA), also known as an Instrument landing System, uses the concept of space modulation to provide guidance to aircraft when on final approach.
The difference between the two modulation depths produce an error current signal in the airborne receiver.