How does a Transceivers Work?
Example 1: The transceiver is 100ft AMSL. Therefore, the range on the ground is 12.3nm. If you are AGL outside of this area, you won't be able to transmit/receive. The aircraft down the bottom is at 35000ft, because of their height, it gives them a range of 230nm. They will be able to broadcast and receive from that transceiver. The higher an aircraft is, the greater range they have.
Example 2: Both aircraft are within range of the transceiver in this photo, however, aren't in range of each other. This means the controller can communicate with both aircraft, however, the aircraft won't be able to hear each other.
Example 3: Another possibility is that an aircraft may be within your range however, isn't in range of the transceiver. This is a situation where you could relay their message to the controller/appropriate traffic.
What about when ATC is offline?
Where a transceiver isn't available, you will have a fixed broadcast range ring of 15nm around your aircraft when tuned to 122.800. If another aircraft (with a range ring of 15nm) is 29nm away from you, you should be able to hear them.
- Adapted from Callum Strawbridge & AFV User Guide Section 4 - https://drive.google.com/file/d/1fLIp1XUnCxPYKTNdzjDo4uKq03ZklTZW/view