Question E2E12:
How do ALE stations establish contact?  

Choices:  
A: ALE constantly scans a list of frequencies, activating the radio when the designated call sign is received  
B: ALE radios monitor an internet site for the frequency they are being paged on  
C: ALE radios send a constant tone code to establish a frequency for future use  
D: ALE radios activate when they hear their signal echoed by back scatter    

Correct Answer is  A: ALE constantly scans a list of frequencies, activating the radio when the designated call sign is received  

---
ALE (Automatic Link Establishment) uses selective calling on a prearranged list of HF channels. Each station scans those channels when idle and listens for short ALE call bursts addressed to its unique ALE address. When a station hears its call, it stops scanning, locks to that frequency, and completes a brief handshake, establishing the link.

Why A is correct:
- ALE constantly scans a programmed channel list and activates (halts scanning) when it receives a valid selective call with its address. This is the standard 2G/3G ALE procedure used on HF, including in amateur ALE.

Why the other choices are incorrect:
- B: No internet dependence. ALE is over-the-air; it does not monitor websites to know where to listen.
- C: ALE does not send constant tones. It uses short burst transmissions (selective calls, soundings, and link setup frames), not continuous tones to “reserve” a frequency.
- D: Backscatter echoes are not part of ALE link setup. The trigger is reception of an addressed ALE call, not hearing one’s own signal via propagation effects.

Useful notes and a simple rule of thumb:
- Stations keep an LQA (Link Quality Analysis) from periodic “soundings” to choose the best channel, but the actual link is initiated by an addressed call heard during scanning.
- Keep scan lists modest to reduce call setup time. If each channel is dwelled on for $t_\text{dwell}$ seconds and there are $N$ channels, the scan cycle time is:
  $$T_\text{cycle} = N \cdot t_\text{dwell}$$
  Smaller $N$ or shorter $t_\text{dwell}$ shortens call setup latency.

This aligns exactly with choice A.