*Question E2E12:
How do ALE stations establish contact?*  

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

### AI Response: (may contain errors)  

Automatic Link Establishment (ALE) is a system used in radio communications to automatically establish a communication link between stations. Here's how it works and why the correct answer is correct:

1. **Correct Answer Explanation:**

   - **Correct Choice: A**  
     ALE constantly scans a list of frequencies, activating the radio when the designated call sign is received.  
     - ALE systems are designed to automatically find the best frequency for communication by scanning a pre-programmed list of frequencies. 
     - When an ALE station receives a call with its designated call sign, it activates and establishes a communication link on that frequency. 
     - This process allows for efficient and reliable communication without manual frequency selection.

2. **Incorrect Choices Explanation:**

   - **Choice B: ALE radios monitor an internet site for the frequency they are being paged on**  
     - This is incorrect because ALE operates independently of the internet. It uses radio frequencies to establish communication links, not internet sites.

   - **Choice C: ALE radios send a constant tone code to establish a frequency for future use**  
     - This is incorrect because ALE does not use constant tone codes. Instead, it uses digital signals to scan and select frequencies dynamically.

   - **Choice D: ALE radios activate when they hear their signal echoed by back scatter**  
     - This is incorrect because ALE does not rely on backscatter signals. It uses direct frequency scanning and call sign recognition to establish links.

3. **Useful Concepts:**

   - **Frequency Scanning:** ALE systems are pre-programmed with a list of frequencies to scan. This list is known as a "channel plan."
   - **Call Sign Recognition:** ALE systems listen for specific call signs to determine when to activate and establish a link.

Understanding these concepts will help you grasp how ALE systems function and why the correct answer is the most accurate description of their operation.