Question E1B02:
[97.307(f)(2)] Which of the following is an acceptable bandwidth for digital voice or slow-scan TV transmissions made on the HF amateur bands?  

Choices:  
A: 3 kHz  
B: 10 kHz  
C: 15 kHz  
D: 20 kHz    

Correct Answer is  A: 3 kHz  

To stay legal on HF, FCC 97.307(f)(2) limits the occupied bandwidth of phone and image emissions (which include digital voice and slow-scan TV) to no more than 3 kHz below 29.7 MHz.

Why A (3 kHz) is correct:
- Digital voice and SSTV on HF are transmitted in the phone/image segments and must fit within $BW \le 3\,\text{kHz}$.
- Common DV and SSTV modes are designed to fit in an SSB passband (about 2–3 kHz).

Why B, C, D are incorrect:
- 10 kHz, 15 kHz, and 20 kHz exceed the 3 kHz HF limit for these emissions, violating 97.307(f)(2).
- Bandwidths like 10–20 kHz are typical of wideband FM on VHF/UHF, not HF SSB phone/image.

Useful rules of thumb and formulas:
- HF phone/image limit: $$BW_{\text{occupied}} \le 3\,\text{kHz}$$
- For SSB-like modes: $$BW_{\text{RF}} \approx BW_{\text{audio}}$$
  - Keep audio cutoff around $2.4\text{–}2.7\,\text{kHz}$ to stay under 3 kHz.
- SSTV example: audio tones roughly 300–2300 Hz, so $$BW \approx 2.3\,\text{kHz}$$
- FM reference (why wider values are wrong on HF): Carson’s Rule $$B \approx 2(\Delta f + f_m)$$
  - Example: $\Delta f=5\,\text{kHz}$, $f_m=3\,\text{kHz}$ gives $B \approx 16\,\text{kHz}$ (typical VHF FM, not HF).