Question E3A09:
Which of the following frequency ranges is most suited for meteor-scatter communications?  

Choices:  
A: 1.8 MHz - 1.9 MHz  
B: 10 MHz - 14 MHz  
C: 28 MHz - 148 MHz  
D: 220 MHz - 450 MHz    

Correct Answer is  C: 28 MHz - 148 MHz  

Correct answer: C — 28 MHz to 148 MHz (10 meters through 2 meters)

1) Why this is correct
- Meteor trails create short-lived ionized columns that can reflect and scatter VHF signals most effectively in the 30–150 MHz region, with a “sweet spot” around 30–50 MHz (6 meters). The 2-meter band (144 MHz) also works, though with shorter pings.
- This range balances sufficient electron density in the trail with wavelengths short enough for efficient scattering but not so high that the signal passes through the plasma.

2) Why the other choices are incorrect
- A: 1.8–1.9 MHz (160 meters): Wavelengths are too long and D-layer absorption is significant. Meteor-scatter is inefficient at LF/HF.
- B: 10–14 MHz (30–20 meters): These HF bands typically use ionospheric F-layer propagation. Meteor-scatter returns are weak/rare and not practical here.
- D: 220–450 MHz (1.25 meters to 70 cm): Frequencies are generally too high; most meteor trails don’t have sufficient plasma frequency for strong reflections, so signals tend to pass through or produce very weak, very brief pings.

3) Useful formulas and rules of thumb
- Plasma frequency threshold for reflection:
  $$f_p(\text{kHz}) \approx 8.98\,\sqrt{N_e\;(\text{cm}^{-3})}$$
  Reflection is favored when $f \lesssim f_p$.
- Practical rule of thumb:
  - Best: 30–50 MHz (6 meters)
  - Usable: up to ~150 MHz (2 meters)
  - Above ~150–200 MHz, returns drop off rapidly
- Typical meteor-scatter single-hop distances: ~500–1,300 km
- Best times: early morning (higher meteor rates) and during major showers

These points explain why 28–148 MHz is the most suited range for meteor-scatter communications.