Radio Amateurs Receive/Decode Signal from 4M Lunar Orbiter

Receiving signals from the moon is a challenge. Although amateur radio operators have been bouncing signals off the moon and receiving them seconds later when they return to Earth since 1953, the effort required very large antennas, high-power transmitters and delicate low-noise amplifiers. The availability of digital modes such as JT65 using software DSP has made it possible to receive signals that are too weak to hear, but receiving signals from the moon still requires either bouncing your own signal off the moon or knowing when someone else is beaming a signal of sufficient power at the moon when it is visible at your location.

Thanks to the Manfred Memorial Moon Mission (4M) that's been carried into space by a Chinese Long March 3C/G2 rocket, radio amateurs have had a chance to monitor JT65B signals being transmitted on 145.980 MHz from the spacecraft as it heads towards the moon. The ARRL reported radio amateurs were hearing the 4M signal after the launch but signals weakened as it approached the moon. On Oct. 27, ARRL reported 4M Moon Orbiter Signals “Quite Weak,” Onboard Messages to Loop. The 4M Amateur Radio payload completed its loop around the moon early on Oct. 28 (UTC), so signals should be getting stronger as the payload starts its long trip back to Earth.

The article 4M Moon Orbiter Completes Lunar Flyby in the Oct. 30 ARRL Letter, describes the payload and notes a high gain antenna is required to receive signals from its quarter wave monopole antenna and 1.5 watt transmitter. Use the tracking calculator on the Manfred Memorial Moon Mission website to determine the coordinates and distance to the 4M spacecraft. Detailed instructions on how to receive the signal are available on the Reception of 4M Signals page.

Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.