Question
Which of the following HF digital modes uses variable-length character coding?
Answer Options
- A) RTTY
- B) PACTOR
- C) MT63
- D) PSK31
Correct Answer: D
Explanation
Most legacy digital modes (like RTTY and Baudot) use a fixed-length character code, meaning every character, regardless of how common, takes the same number of bits to transmit. This is simple but inefficient. More modern modes seek to improve efficiency by using compression techniques based on the likelihood of a character appearing.
PSK31 uses a specialized coding scheme called Varicode, which is a variable-length character coding similar to Morse Code. Varicode assigns shorter code strings to the most frequently used letters and symbols and longer strings to less common characters. This technique significantly increases the overall data throughput and efficiency for conversational text compared to older fixed-length codes.
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