simultaneously transmit weather and mapping beams.

eliminate the need for azimuth slaving.

greatly reduce lateral lobes, consequently concentrating more energy into the main beam.

produce a wide beam for better target detection.

in HF two-way communication.

in VHF transmissions to reduce transmission power.

with transmissions of the Meteorological aerodrome Report (METAR)

with NDB transmissions to reduce the bandwidth

A frequency.

Distance.

An amplitude.

Time.

Altitude is too high.

The power of the transmitted signal is too weak to be received by the DME station.

Aeroplane is circling around the station.

Aeroplane is below the minimum altitude for line of sight propagation.

Amplitude modulated to transmit the Morse code ident, as is used by a VOR.

A continuous wave interrupted with a keyed Morse code ident as used by an NDB.

Interrupted to transmit the Morse code identification, as used by an NDB.

Amplitude modulated by a speech signal, such as is used for VHF-COM.

It needs a higher elevation than 55° above the horizon.

It needs a higher elevation than 5° above the horizon.

It needs a higher elevation than 15° above the horizon.

It needs a higher elevation than 5° below the horizon.

the solar wind and the gravitation of the Sun, moon and planets.

Earth and lunar precession.

solar and lunar precession.

the lunar wind and the gravitation of the Earth, moon and stars.

6 minutes.

3 hours.

6 seconds.

3 seconds.

the integrity is improved by reducing the mean failure reporting time from up to 3 hours to 6 seconds

no improvements are obtained apart from the redundancy

the errors caused by multi path and noise are eliminated.

the errors caused by multi path and noise are eliminated. 

a better position accuracy is obtained but the integrity of the system is not improved. 

By the SSR interrogator if it is suspected that responses are received from aircraft that are located in thedirection of the side lobes of the interrogator antenna.

By the SSR interrogator in order to request the identification of an aircraft.

Automatically when the transponder responds to a mode A interrogation.

By the transponder as a result of the pilot pushing the IDENT button.