Question E2E05:
Which of these digital modes does not support keyboard-to-keyboard operation?  

Choices:  
A: WSPR  
B: RTTY  
C: PSK31  
D: MFSK16    

Correct Answer is  A: WSPR  

WSPR is correct because it is not a conversational (keyboard-to-keyboard) mode. It is an automated weak-signal propagation reporting mode that sends a fixed, highly compressed message (callsign, grid, power) on a strict time schedule for reception reports, not free-text QSOs.

Why WSPR (A) is correct:
- WSPR = Weak Signal Propagation Reporter.
- Sends a structured message only (no free text), typically: callsign, 4- or 6-character grid, and power.
- Time-synchronized, 2-minute cycles with about 110.6 s transmit.
- Very narrow 4-FSK (~6 Hz), symbol rate about $1.4648$ baud.
- Purpose: mapping propagation paths via automatic reports (WSPRnet), not real-time chat.

Why the others are incorrect (they do support keyboard-to-keyboard):
- RTTY (B): Classic conversational mode; typical settings are $45.45$ baud, $170$ Hz shift; free-text typing in real time.
- PSK31 (C): Designed for keyboard QSOs; $31.25$ baud BPSK/QPSK; very narrow (~31 Hz) and efficient for live typing.
- MFSK16 (D): 16-tone MFSK with FEC; robust for weak signals; intended for real-time keyboard exchanges.

Useful rules of thumb:
- Conversational (keyboard-to-keyboard) examples: RTTY, PSK31, MFSK/Olivia.
- Non-conversational, structured/automated examples: WSPR, FT8, JT65, JT9, FT4.
- Approximate symbol rates:
  - RTTY: $45.45$ baud
  - PSK31: $31.25$ baud
  - MFSK16: $15.625$ baud
  - WSPR: $1.4648$ baud (4-FSK), message length ~50 bits user data with heavy FEC/interleaving

Key idea: If the mode is designed for propagation reporting or highly structured exchanges with strict timing and no free-text, it is not keyboard-to-keyboard.