Question E2D09:
What type of modulation is used by JT65?  

Choices:  
A: Multitone AFSK  
B: PSK  
C: RTTY  
D: QAM    

Correct Answer is  A: Multitone AFSK  

To identify JT65’s modulation, remember it sends information as many discrete audio tones into an SSB transmitter (audio tones shifted to RF). That makes it multitone AFSK (i.e., MFSK done at audio).

Why the correct answer is correct
- JT65 uses 65 distinct audio tones to convey symbols.
- These tones are generated in audio and fed to an SSB radio, so it is audio-frequency shift keying: Multitone AFSK.

Why the other choices are incorrect
- PSK: Phase shift keying changes phase, not frequency. JT65 changes among many frequency tones, not phase.
- RTTY: Classic RTTY is 2-tone FSK (typically 170 Hz shift, 45.45 baud), not a 65-tone scheme.
- QAM: Quadrature amplitude modulation varies both amplitude and phase with a constellation. JT65 does not use amplitude or phase constellations.

Useful formulas / rules of thumb
- Rule of thumb: WSJT “JT” modes are multitone AFSK via SSB.
  - JT65 = 65-tone AFSK (MFSK)
  - JT9 = 9-tone AFSK
  - FT8 = 8-FSK (also AFSK via SSB)
- Bandwidth estimate for multitone FSK:
  $$BW \approx \Delta f \times (N - 1)$$
  where $N$ is the number of tones and $\Delta f$ is the tone spacing.
  For JT65, $\Delta f \approx 2.69$ Hz and $N=65$, so $BW \approx 2.69 \times 64 \approx 172$ Hz (about 175–180 Hz in practice).