Ham Radio Extra Class Practice Test 2025 - Free Extra Class License Exam Questions and Study Guide

Question: 1 / 400

Which of the following HF digital modes uses variable-length coding for bandwidth efficiency?

RTTY

PACTOR

MT63

PSK31

PSK31 utilizes variable-length coding to achieve bandwidth efficiency, making it well-suited for digital communication in HF bands. This mode is designed to transmit text and uses a unique encoding scheme that allows it to adapt to the amount of data being transmitted. By using variable-length character codes, PSK31 can transmit shorter messages using less bandwidth and can expand to fit more complex messages when necessary.

On the other hand, RTTY (Radio Teletype) employs a fixed length for its character encoding which does not lend itself to variability based on message length. PACTOR, while advanced in terms of error correction and speed, also does not utilize variable-length coding in the same way. MT63 operates on a fixed number of bits per character as well. Thus, PSK31 stands out for its ability to adjust the bandwidth usage based on the amount of data, making it the most efficient choice among the options provided.

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