Everybody loves a good moon bounce. Today's moon bounce didn't involve taking your shoes off and jumping, but it was every bit as fun (if you are a geek). Every so often, when the moon is in the right spot, amateur radio operators ("hams") organize a competition to see who can communicate with the most people across the world by bouncing signals off of the moon. Today was the "Echoes of Apollo Moon Bounce" event -- a global ham celebration of the 40th anniversary of the Apollo 11 mission. The NY Times did a decent overview of the event.
I spent a good chunk of the day listening to these signals. Growing up, my dad was often in the basement with his radios or on the roof tweaking his antennas. I was always fascinated by his equipment and the people he talked to from all over the world, but by the time I got old enough to really get into it I had been bit by the computer bug. My dad sometimes compared what I was doing at age 12 with BBS'es and my 2400 baud modem with some of his ham radio passions. I still remember my first VoIP experience in the early 90's, talking to an Australian guy over dialup.
I never did get my ham radio license, in part because of the pull of computers and the burgeoning internet. Nevertheless, in the years since then I've gained a greater appreciation of the radio spectrum. Spectrum is a valuable shared resource that we have allocated to different users for communication. Sometimes we have tried to choose who is the most important, sometimes we have auctioned use of it off to the highest bidder, and other times we have allowed a "commons" oriented unlicensed use. New technologies shape the way we are able to use this common good, and we have plenty of active policy debate over these issues. Just yesterday I watched a New America Foundation event that was "optimistically" titled "The End of Spectrum ‘Scarcity': Opportunistic Access to the Airwaves."
Amateur radio operators have traditionally operated via analog means as they communicate by voice or morse code. Over time, they incorporated packet radio, allowing computers to transmit over certain frequencies using special analog-to-digital hardware. In the time since my dad's basement tinkering and my first modem, the worlds of radio and computer -- analog and digital -- have converged. The latest example of this was of course the analog-to-digital transition for broadcast television in the United States, and the extent to which this opens up unused "white spaces" for broadband. The most important innovation in wireless digital communications has been the emergence of Software Defined Radio ("SDR") technology that allows tuning, transmitting, and receiving to be done in software instead of special hardware. This means that computing devices can become general purpose radios, and whereas my dad used to have to buy new transistors and diodes at the hamfest, I can just download and install a new radio image for my Android phone.
Receiving the Earth-Moon-Earth ("EME") transmissions requires a decent parabolic antenna, but I don't have one. So how did I spend the day listening to radio signals bouncing off of the moon? I tuned in via a Dutch dish that was streaming online. Now, it would be pretty cool if the operators of this dish were simply tuning around for signals and sending a single audio stream out to anyone who wished to listen. However, what they did was even cooler. They captured all of the data for a frequency band (1.24-1.3 GHz, what the hams call "23 cm" because of the wavelength) and then they published a web-based application for SDR decoding on that raw stream so that each person could tune to any transmission within that band! The interface includes a draggable tuner and live spectrum analyzer output of signals. You can actually see what location on the dial every other person is tuning to. This combination of SDR and internet-enabled interactivity just blew my mind. I chatted briefly with the folks in the Netherlands:me: geek question: does websdr send all of the receiver data to the end-user and then the java app tunes locally, or is the java app instructing the server how to process before sending the stream?
them: The latter. The raw data stream would be about 3 Mbit/s, that would be too much for many home connections.
me: sdr is on the main cpu or other boards?
them: On the main CPU. The only external hardware is an analogue downconverter.
It really was fun to listen to the moon bounce, and the web-based experience just reinforced how much is possible in the radio spectrum when it is combined with computing. The traditional model of frequency allocation for a specific purpose needs to give way to more efficient spectrum-sharing techniques. The amateur radio operators have developed sophisticated social norms for sharing their radio waves, but they are highly inefficient when compared to something like WiFi, which is in turn highly inefficient compared to more modern approaches. As an example of what a bridging experience the moon bounce was for me, the signal was arriving in the 1.2 GHz band in the Netherlands, which then was piped over the internet to my house and then re-transmitted to my laptop over WiFi at 2.4 Ghz.
As a policy matter, digitization of the airwaves means that we need to re-think how we use them. Today, computers can directly connect and transmit more in a millisecond than an entire ham radio back-and-forth ("CQ, CQ, CQ..."). We need a map of the vast swaths of unused spectrum, and an automated digital means for sharing them. That's part of the upcoming National Broadband Plan being created by the FCC.
That's not to say that ham radio should go away. The thrill of finding a remote station in Russia, the Netherlands, London or Mexico and tuning it in for that brief moment is quite an experience. Everybody loves a moon bounce.
Here are a few excerpts I captured while I was listening (sorry about the lousy tuning in a couple places, it just makes it sound more like the Death Star attack from Star Wars):
