Deep Dive: E2E03
The correct answer is B: Four-tone continuous-phase frequency shift keying. To what does the '4' in FT4 refer is four-tone continuous-phase frequency shift keying. FT4 uses four tones with continuous-phase FSK. For amateur radio operators, this is important for FT4 operation. Understanding this helps when operating FT4.
Why Other Answers Are Wrong
Option A: Incorrect. Multiples of 4 bits of user information isn't what the '4' refers to - it refers to four-tone FSK. Bits isn't the '4'. Option C: Incorrect. Four transmit/receive cycles per minute isn't what the '4' refers to - it refers to four-tone FSK. Cycles per minute isn't the '4'. Option D: Incorrect. Since A and C are not correct, 'all of the above' cannot be correct. Only four-tone FSK is correct.
Exam Tip
FT4 '4' = four-tone continuous-phase frequency shift keying. Think 'F'T'4' = 'F'our-'T'one 'F'SK. FT4 uses four tones with continuous-phase FSK. Not 4 bits, not 4 cycles per minute - just four-tone FSK.
Memory Aid
FT4 '4' = four-tone continuous-phase frequency shift keying. Think 'F'T'4' = 'F'our-'T'one. FT4 uses four tones with continuous-phase FSK. Important for FT4 operation.
Real-World Example
FT4 mode: The '4' in FT4 refers to four-tone continuous-phase frequency shift keying. FT4 uses four different tones (frequencies) with continuous-phase frequency shift keying. This is what the '4' means - four-tone continuous-phase FSK.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E2E
Reference: 2024-2028 Question Pool · E2 - Operating Procedures
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E2E topic.