E2E12

How do ALE stations establish contact?

1. AALE constantly scans a list of frequencies, activating the radio when the designated call sign is received
2. BALE radios monitor an internet site for the frequency they are being paged on
3. CALE radios send a constant tone code to establish a frequency for future use
4. DALE radios activate when they hear their signal echoed by back scatter

Pick an answer to check it.