Question E2C04:
Which of the following frequencies can be used for amateur radio mesh networks?  

Choices:  
A: HF frequencies where digital communications are permitted  
B: Frequencies shared with various unlicensed wireless data services  
C: Cable TV channels 41-43  
D: The 60-meter band channel centered on 5373 kHz    

Correct Answer is  B: Frequencies shared with various unlicensed wireless data services  

Correct answer: B — Frequencies shared with various unlicensed wireless data services

1) Why B is correct
- Amateur mesh networks (HSMM/AREDN) use wideband, Wi‑Fi-like signals on amateur allocations that overlap unlicensed Part 15 services (e.g., 902–928 MHz, 2390–2450 MHz, 5650–5925 MHz). These shared bands allow hams to use modified Wi‑Fi gear under Part 97 for mesh networking.

2) Why the others are incorrect
- A: HF frequencies where digital communications are permitted
  - Mesh uses wide channels ($\approx 5$–$20$ MHz) and often spread spectrum/OFDM. HF digital segments are narrow (a few kHz) and cannot accommodate Wi‑Fi‑type wideband. Also, spread spectrum is only permitted for $f \ge 222$ MHz.
- C: Cable TV channels 41–43
  - CATV channels are for cable systems, not over‑the‑air amateur allocations. Transmitting over the air on these channel frequencies would be outside amateur bands.
- D: The 60‑meter band channel centered on 5373 kHz
  - 60 m is channelized and limited to narrowband emissions (occupied bandwidth $\le 2.8$ kHz) and specific modes. Mesh/Wi‑Fi‑type signals are far wider and not permitted there.

3) Useful rules of thumb
- Mesh/HSMM bands commonly used by amateurs:
  - 33 cm: $902$–$928$ MHz
  - 13 cm: $2390$–$2450$ MHz
  - 5 cm: $5650$–$5925$ MHz
- Spread spectrum in the amateur service: allowed only for $f \ge 222$ MHz.
- Typical mesh channel widths: $\approx 5$, $10$, or $20$ MHz.
- 60 m: occupied bandwidth limit $\le 2.8$ kHz; not for high‑speed, wideband data.