What characterizes libration fading of an EME signal?
A slow change in the pitch of the CW signal
A fluttery, irregular fading✓Correct answer
A gradual loss of signal as the sun rises
The returning echo is several hertz lower in frequency than the transmitted signal
Explanation
The Moon's surface is rough and its libration slowly changes which facets face the Earth, so the echo returns as many reflections whose path lengths and Doppler shifts drift relative to one another and add and cancel at random, producing fluttery, irregular fading. A steady change of pitch or a constant few-hertz offset is a plain Doppler effect of relative motion, and sunrise has no bearing on a lunar echo.