Only about 1,000 ham radio buffs worldwide have the equipment to bounce a signal off the moon.
PALO ALTO, Calif. — Dogs bay at it. Lovers swoon under it. And some people like to bounce their voices off it.
Michael Cousins, an engineer at SRI International, a non-profit that operates the dish, center, in the control room, with Ham operators Lance Ginner, left, and Jim Klassen.
A radio dish at Stanford is powerful enough to bounce signals off the moon, a tricky endeavor.
The first two are easy, but sending a voice signal 239,200 miles to the moon and back is not quite as simple.
On Saturday, amateur radio buffs or “hams,” as they call themselves, will hold a global bounce-fest, using as many giant parabolic antenna radio telescopes as they can borrow around the world.
Not that one needs an excuse to hold a moon-bounce, but this one is being held as a kind of advance celebration of the 40th anniversary next month of the Apollo 11 mission.
Moon-bouncing, also known as Earth-Moon-Earth communications, or E.M.E. requires a higher grade of ham-radio technology than that used for traditional earth-bound communication across parts of the radio spectrum approved by governments for amateur use. Only about 1,000 hams worldwide have stations capable of moon-bouncing.
Skill and luck also help. As the hams say, the moon is a poor sounding board, since it is spinning and has a rough surface that can disrupt signals. The hams’ voices must survive atmospheric interference over the long round-trip journey in a discernible form.
“It’s the equivalent of climbing Mount Everest in amateur radio,” said Joseph H. Taylor Jr., a Nobel Prize winner and retired physics professor from Princeton University who has written software to help radio buffs communicate via weak signals. “It’s possible, but only barely possible.”
Large dishes like those owned by the government and communications companies can solve many of these problems by making it easier to send and receive signals. That’s why the hobbyists have searched out retired or rarely used dishes. So far, operators of about 20 large dishes in the United States, Australia and Europe have agreed to participate in the event.
One of them is located on a hill overlooking Stanford University’s campus, and will serve as the command center for the weekend’s event. Known simply as the Dish, the 150-foot-wide antenna, owned by the federal government, will be outfitted with special equipment and a computerized tracking system to keep a powerful, focused signal on the moon.
A handful of radio enthusiasts have been working on the structure over the last few weeks, huddling inside a central command center below the towering, rusting web of metal. They gathered around whirring communications gear as if it were a campfire and chortled with satisfaction when their “hellos” bounced back from the moon 2.5 seconds later.
There is a point beyond the “because it’s there” challenge.
The hams also hope to inspire young technology buffs. “People think of ham radio as something Grandpa did down in the basement while he smoked and talked to people around the world,” said Pat Barthelow, who has organized the worldwide moon-bounce, called Echoes of Apollo. “I think moon-bounce retains an exoticness and difficulty that can hook some people and bring ham radio into the modern era.”
Creating a homemade radio capable of hitting the moon can require years of tweaking custom components. The setups cost $200 to $2,000.
The United States military began bouncing radio signals off the moon in the 1950s to communicate over long distances when other transmission methods were hampered by atmospheric disruptions. By the mid-1960s, operators at large dishes started building amateur systems capable of moon-bouncing. In 1964, Michael Staal accomplished the feat, linking a setup at Stanford to another one in Australia.
“I got famous very quickly,” said Mr. Staal, who sells antennas to ham radio operators.
Moon-bouncers often hold contests where they must hunt around different frequencies and both send and receive a signal with another station, logging their activities for review. They’re forbidden from communicating with each other via non-lunar means during the contests, and often win a certificate or free subscription to a ham magazine as prizes for making contact with as many others hams as they can.
“It is the thrill of pulling a weak signal out from a long distance that excites the amateur radio folks,” said Jim Klassen, a ham in Reedley, Calif.
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