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What is the reason that a DME-station can generally respond to a maximum of 100 aircraft?
  • A
    The minimum allowable accuracy of the range-measurement cannot be guaranteed when more than about 100 aircraft are using the same DME-station.
  • B
    The number of reply pulse pairs per second that a DME-transponder can transmit is limited to a certain maximum value.
  • C
    The automatic ground monitoring station of each DME-station has a limited capacity.
  • D
    The memory of the DME-transponder is limited.

The response function of a DME transponder involves a continuous process that operates at a transmission rate of 2 700 pairs of pulses per second (ppps). Once the transponder starts receiving pulses at this rate, it reaches a state of saturation, leading to an automatic reduction in its receiver gain. This adjustment has the consequence of filtering out transmissions from aircraft whose interrogation pulses are relatively weaker.

In practical terms, this translates to approximately 100 aircraft concurrently utilizing the DME system.

The fortunate group of 100 consists of those aircraft emitting the most potent interrogation signals, rather than necessarily being the closest ones. When the ground-based DME station undergoes saturation, it exclusively acknowledges the 100 most robust signals.

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