Question E2E08:
Which of the following HF digital modes can be used to transfer binary files?  

Choices:  
A: PSK31  
B: PACTOR  
C: RTTY  
D: AMTOR    

Correct Answer is  B: PACTOR  

To transfer binary files over HF, you need a mode that is 8-bit transparent and uses robust error control (ARQ/FEC). PACTOR fits this; the others are primarily text/keyboard modes.

1) Why PACTOR is correct
- PACTOR (especially II/III/IV) supports 8-bit transparent data, ARQ (Automatic Repeat reQuest), and strong FEC/compression.
- It is specifically designed for reliable file and email transfer over HF (e.g., Winlink).

2) Why the other choices are incorrect
- PSK31: A narrowband keyboard-to-keyboard text mode using varicode; not 8-bit transparent and lacks ARQ for binary file transfer.
- RTTY: Uses 5-bit Baudot (ITA2) with LTRS/FIGS shifts; character-oriented, no ARQ/FEC, not suitable for arbitrary binary data.
- AMTOR: An ARQ/FEC text mode based on CCIR 476 (4-of-7 code); character-oriented, not 8-bit transparent, so not used for binary files.

3) Useful rules of thumb
- For HF binary file transfer, look for ARQ-capable, 8-bit transparent modes: PACTOR (also Clover, ARDOP, VARA in modern practice).
- Keyboard/text-only modes (RTTY, PSK31, AMTOR) are for human-readable text, not arbitrary binary files.