What is the Moonbounce (EME) communication technique?

Moonbounce, also known as Earth-Moon-Earth (EME) communication, is an advanced amateur radio technique that involves bouncing radio signals off the Moon’s surface to communicate with other stations on Earth. This method allows radio operators to make contacts over vast distances, even thousands of kilometers, without relying on traditional propagation methods such as ionospheric reflection or satellite relays.

Here’s an overview of the Moonbounce (EME) communication technique:

How it works

In EME communication, a radio operator transmits a signal towards the Moon, which reflects the signal back to Earth. Another operator, located far away, receives the reflected signal. This process requires precise timing, antenna pointing, and signal processing to overcome the significant path loss and signal degradation caused by the long journey to the Moon and back.

Frequency bands

EME communication typically takes place on VHF, UHF, and microwave frequency bands, where the Moon’s surface reflects radio signals more efficiently. The most popular bands for EME are the 2-meter (144 MHz), 70-centimeter (432 MHz), and 23-centimeter (1296 MHz) bands.

Equipment

EME communication requires specialized equipment, including:

• High-gain antennas: Large, directional antennas, such as Yagi, parabolic dish, or array antennas, are necessary to focus the transmitted signal towards the Moon and capture the weak reflected signals.
• High-power amplifiers: Due to the significant path loss associated with EME, high-power amplifiers are needed to increase the transmitted signal strength and improve the likelihood of successful communication.
• Low-noise preamplifiers: Low-noise preamplifiers on the receiving side help amplify the weak reflected signals while minimizing additional noise.
• Accurate antenna pointing: To ensure accurate antenna pointing, operators use computer-controlled antenna rotators and tracking software that takes into account the Moon’s position, elevation, and azimuth relative to the operator’s location.

Modes of communication

EME communication typically uses weak-signal modes, such as CW (Morse code) or digital modes like JT65 and QRA64. These modes have been specifically designed to decode and interpret weak signals, even when they are below the noise level.

Challenges

EME communication presents several challenges, including:

• Signal path loss: Due to the long distance and the Moon’s irregular surface, EME signals experience significant path loss, which can exceed 250 dB.
• Doppler shift: As the Earth and the Moon move relative to each other, the frequency of the reflected signals shifts, requiring operators to adjust their transceiver frequency accordingly.
• Polarization: The polarization of radio signals can change as they reflect off the Moon, making it necessary to use circular polarization or dual-polarization antennas to maximize signal reception.

Despite these challenges, many amateur radio operators find EME communication to be a rewarding and fascinating aspect of the hobby. The thrill of making contacts by bouncing signals off the Moon, combined with the technical challenges and achievements, makes Moonbounce communication an exciting pursuit for experienced radio enthusiasts.