Which of the following is characteristic of the FST4 mode?
Four-tone Gaussian frequency shift keying
Variable transmit/receive periods
Seven different tone spacings
All these choices are correct✓Correct answer
Explanation
FST4 uses four-tone Gaussian frequency shift keying, offers seven sequence lengths from 15 seconds to 30 minutes, and gives each of those sequence lengths its own tone spacing, from 16.67 Hz down to 0.089 Hz. All three descriptions are therefore correct.