Bouncing off the moon

Earth–Moon–Earth communication (EME), also known as Moon bounce, is a radio communications technique that relies on the propagation of radio waves from an Earth-based transmitter directed via reflection from the surface of the Moon back to an Earth-based receiver.

The first experiments and successful communication goes back to the early 1940s. During and after WW2 the moon was used as a reflector for bouncing radar waves for defence, communication and radio astronomy purpose.

However, with the advancement of satellites, the moon became obsolete and since 1960, radio amateurs are the main ‘users’.

To amateurs, EME presents significant challenges in regards to weak signal communication. EME provides the longest communications path any two stations on Earth can use and it takes 2.5 seconds for the signal to reach the moon and bounce back. Frequencies from 50 MHz to 47 GHz have been used successfully, but most EME communications are on the 2 metre, 70 centimetre, or 23 centimetre bands. Recent advances in digital signal processing have allowed EME contacts to take place with powers in the order of 100 watts and a single Yagi antenna.

To many, EME is the last frontier of amateur radio and completing a two-way contact is regarded as a significant achievement.

This weekend, I managed to complete two EME contacts using a single 5 element yagi antenna, on 6m band. Of course, this was possible due to the fact that both of my correspondents had much larger antenna systems which allowed them to detect my weak signal. Also, unlike my antenna being ‘fixed’ to the horizon (no elevation) their large antennas could be elevated to point directly at the moon. This is quite a mechanical challenge due to antenna weight and wind resistance, so a large part of the credit goes to them, DL8YHR and KJ9I. I’ve also decoded G4BWP numerous times which is a sign that despite a very modest receiving antenna, my location has very low noise on 6m band.

If you have a single yagi antenna and relatively quite location you should try EME. Probably not on 6m band, but definitely on 2m, especially if your antenna could be rotated and elevated. Six metres is more challenging than 2 metres, and there are only a handful of ‘big gun’ EME setups out there. A few years ago, I completed two dozen 2m EME contacts with a single antenna and 100 Watts from Sydney, before the local noise became unbearable. 

However, EME is not a ‘plug-and-play’, nor should you expect that you will get it all sorted out in a day or two. The project starts with selecting a good, proven antenna design, then getting the antenna high above the ground. Every decibel matters. Accurate moon tracking, low loss feed-line. Amplifier mounted close at antenna feed point is preferred but not absolutely necessary, at least in the initial stage.

If you already have a decent antenna, but never tried EME, then I strongly suggest to get yourself familiar with some basic astronomy essentials: moon rise, moon set, sky noise, path losses. In the old days, all the calculations were done manually, but nowadays, thanks to software like VK3UM EME planner, all the relevant data could be extrapolated with one click. Also, you should be an advanced user of a decoding software like WSJT-x; there are mode-specific settings required for EME operation.

Once you are set to receive – find a big gun station and ask him to transmit for you. If you are lucky, you may see signals coming your way, bounced off the moon. And if you do, you are probably ready to transmit.

Of course, there is no guarantee that you will be successful on the first go. Even the big guns don’t take EME for granted, and there are days and times when even the most experienced, best equipped can’t make it ”over the moon”. EME will test your patience. However, the reward would be worth the trouble, and joining the small and elusive EME club of those who are capable of bouncing their signal off the moon is still a pinnacle of ham radio.  

See you on the moon!

Now, if you are the kind of guy who hates digital modes, then all power to you. Here is your challenge: build an antenna setup that would allow you to bounce your voice off the moon. Like the lady in this short video:
https://youtu.be/IjqufZncvrY?si=l0_qDrY_Hz-ak0K9

If this doesn’t blow you away, then nothing will.