EME Basics

Radio hams have been bouncing signals off the moon, and hence having QSOs across the world via the moon, for the past seventy years. It’s termed moonbounce or EME (Earth-Moon-Earth communications). The attraction is obvious: just to be able to say, “I bounce signals off the Moon”, has kudos. Here’s some background.

EME path loss

The EME path loss relies on the Moon being an effective reflector. The transmitted power incident on the Moon is initially captured and then re-radiated. In such a scenario, the path loss between transmitter and receiver comprises the loss in the first leg, the loss or gain of the reflection and the loss in the second or return leg. Here’s the detail.

EME path budget

Before setting out on an expensive project, I wanted to know why EME works and where the sensitivities lie. I couldn’t find any site that described this properly. So, I’ve set out my calculations and rationale for this exciting element of the hobby of ham radio here. It certainly shows the knife edge 144MHz moonbounce sits on – it works, but only just.

The Moon as reflector

The Moon as reflector is complicated. I’ll try to build an explanation here and on other pages. When viewed from a station on Earth, the received signal will be a vector sum of all arrivals from the reflection scenario. The receiver will experience fading, with a median value and discrete values in time distributed about that median. This fading is termed libration fading, caused by the libration movement. Here’s more.

EME bibliography

A page listing various useful references associated with EME. Critical examples include the determination of the sensitivity of JT65 with reference to the Shannon limit, and typical noise figures of 144MHz receivers. More…

Coming soon…


EME station configuration

EME antennas

EME Free space loss

EME polarisation losses

EME anomalous path effects

EME system value

EME outcomes