Moonbounce, or EME (Earth-Moon-Earth), uses the Moon as a passive reflector. You point your antenna at the Moon, transmit, and about 2.5 seconds later your signal comes back to Earth, where any station that can see the Moon at the same time can hear it. That opens up VHF and UHF contacts between continents.
The catch is distance. The round trip is nearly half a million miles, and the Moon reflects only a small part of what reaches it. On 2 m the total path loss is about 252 dB, so the returning signal is usually far below the noise. Even so, hams completed the first two-way amateur EME contact in 1960, on 1296 MHz.
Digital modes changed who can take part. JT65 in WSJT-X was designed for EME, and Q65 is now the recommended EME mode, using one-minute periods (Q65-60A on 6 m and 2 m). These modes decode signals you could never hear by ear.
Big stations with arrays of many Yagis or large dishes do much of the heavy lifting, and they make it possible for much smaller stations to work them. The ARRL Handbook’s EME chapter, written by K1JT, describes a station with one long Yagi and 100 watts on 1296 MHz working dozens of DXCC entities.
Two effects shape what you hear. Doppler shift moves the echo off frequency as Earth turns and the Moon moves, by up to about 440 Hz on 2 m and about 4 kHz on 1296 MHz; WSJT-X can track and correct for it. Libration fading comes from the Moon’s rough surface: your signal bounces off many spots at slightly different distances, and those pieces add and cancel, giving a fast, irregular flutter.
WSJT-X also has an Echo mode that lets you detect your own signal returning from the Moon, a good test of your station. The ARRL band plan sets aside 144.00 to 144.05 MHz for CW EME, 144.10 to 144.20 MHz for EME and weak-signal SSB, and EME segments on 70 cm and 23 cm.
EME stations often pair high power with high-gain antennas, and that combination can create strong RF fields. Do the RF exposure evaluation the rules require, and keep people well away from the front of the array whenever you transmit.
At a Glance
- Category
- Propagation
- On the air since
- 1960
- Echo delay
- About 2.5 seconds
- Path loss
- About 252 dB on 2 m
- Modes
- Q65 and JT65 in WSJT-X, plus CW for larger stations
- Where to listen
- 144.00 to 144.20 MHz, 432.00 to 432.07 MHz and 1295.80 to 1296.08 MHz