Question E2C09:
What type of equipment is commonly used to implement an amateur radio mesh network?  

Choices:  
A: A 2-meter VHF transceiver with a 1,200-baud modem  
B: A computer running EchoLink to provide interface from the radio to the internet  
C: A wireless router running custom firmware  
D: A 440 MHz transceiver with a 9,600-baud modem    

Correct Answer is  C: A wireless router running custom firmware  

Correct answer: C — A wireless router running custom firmware

1) Why C is correct
- Amateur radio mesh networks (often called HSMM or AREDN) commonly repurpose off-the-shelf 802.11 wireless routers or outdoor Wi‑Fi devices.
- Custom firmware (e.g., AREDN, OpenWrt with OLSR) enables Part 97 operation, ad hoc mesh routing, and use of amateur-only channel segments and higher power/antennas.
- These routers form a self-discovering, self-healing IP mesh capable of multi-megabit links.

2) Why the other choices are incorrect
- A: A 2-meter VHF transceiver with a 1,200-baud modem
  - That is classic AX.25 packet at 1200 bps—far too slow for typical mesh applications and not a self-forming 802.11-style mesh.
- B: A computer running EchoLink to provide interface from the radio to the internet
  - EchoLink is an internet VoIP linking system using centralized servers; it is not an RF mesh network.
- D: A 440 MHz transceiver with a 9,600-baud modem
  - 9600 bps packet is still orders of magnitude slower than Wi‑Fi-based mesh and does not implement IP mesh routing by itself.

3) Useful formulas and rules of thumb
- Free-space path loss (for link budgeting):
  $$FSPL_{dB} = 32.44 + 20\log_{10}(f_{MHz}) + 20\log_{10}(d_{km})$$
- Mesh throughput over same-channel hops tends to drop roughly by half per hop:
  $$R_n \approx \frac{R_0}{2^n}$$
  where $R_0$ is the single-hop throughput and $n$ is the number of additional hops.