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Under which circumstances may you expect a solid reception of the TOWER frequency 118.2 MHz?
  • A
    Aircraft at low level but far away from the ground station.
  • B
    Aircraft at low level, far away from the ground station, in the radio shadow zone of a hill.
  • C
    Aircraft at high level in the vicinity of the ground station.
  • D
    Aircraft at low level, in the vicinity of the ground station, in the radio shadow zone of a hill.
VHF PROPAGATION
VHF atmospheric propagation is line of sight, which means waves travel in a direct path from the source to the receiver. A number of factors, some of which are less obvious than others, can have a significant impact on your communication. Obstacles, hill, mountains and, also, the roundness of the Earth itself, greatly reduce the range of reception => Therefore, the direct path/line between the sender and the receiver should be as free of obstacles as possible. Hence low levels flight reduces the range of reception.
The line of sight range can be calculated using the formula:
  • Range (NM) = 1.23 × (√hTX + √hRX) 
    hTX : Transmitter height in feet
    hRX : Receiver height in feet

It does not matter how powerful the transmitter is, if the receiver is below the line of sight range, it will receive nothing.

=> The signal strength will be higher if flying at high level and close to the ground station - to avoid interference from any obstructions.

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