Question E3A03:
When scheduling EME contacts, which of these conditions will generally result in the least path loss?  

Choices:  
A: When the Moon is at perigee  
B: When the Moon is full  
C: When the Moon is at apogee  
D: When the MUF is above 30 MHz    

Correct Answer is  A: When the Moon is at perigee  

Correct answer: A — When the Moon is at perigee

Why A is correct:
- EME path loss is dominated by free-space loss, which increases with distance.
- At perigee the Earth–Moon distance is minimum, so free-space loss is minimum and signals are strongest.

Useful formulas and rules of thumb:
- One-way free-space path loss:
  $$\text{FSPL}_{1\text{-way}}(dB) = 32.44 + 20\log_{10}\!\big(f_{\text{MHz}}\big) + 20\log_{10}\!\big(d_{\text{km}}\big)$$
- For EME (up and back), the distance term doubles:
  $$\text{FSPL}_{2\text{-way}} \propto 40\log_{10}(d)$$
- Path loss difference between apogee and perigee:
  $$\Delta L \approx 40\log_{10}\!\left(\frac{405{,}500}{363{,}300}\right) \approx 1.9\ \text{dB}$$
  So perigee gives roughly a 2 dB advantage—very valuable for weak-signal EME.

Why the other choices are incorrect:
- B: When the Moon is full  
  The Moon’s phase affects illumination, not the Earth–Moon distance. Path loss depends on distance, not phase, so “full” provides no inherent path-loss benefit.
- C: When the Moon is at apogee  
  Apogee is the maximum Earth–Moon distance, which increases free-space loss and makes EME contacts harder.
- D: When the MUF is above 30 MHz  
  MUF refers to ionospheric HF/VHF skywave propagation. EME is a line-of-sight space path via the Moon; MUF is irrelevant to EME path loss.

Extra tip:
- Also prefer higher Moon elevation to reduce ground noise and atmospheric absorption, but distance (perigee) is the key factor asked here.