Audio Clip
(46 seconds, 493 Kb)
Many people think radio astronomy is beyond the reach of the average amateur. After all, who can afford stadium-sized antennas arranged in New Hampshire-sized arrays to gather radio waves from invisible objects at the other end of the universe? However, right here in our solar system, Jupiter is pumping out megawatts of radio energy on the shortwave bands. Even the cheapest, home-made transistorized receiver attached to the simplest antenna can pick up these signals. In fact, if you regularly listen to the decameter bands, (18 - 24 MHz), chances are that you've already heard Jupiter without realizing it.
This excerpt was captured on October 4th, 1998 at 1:47 UTC. The receiver was an ICOM IC-728. The antenna was a piece of #18 insulated wire going out a second floor window into a tree 128 feet away. It ran parallel to the ground, 12 feet up. An antenna tuner was used to match the high impedance antenna to the low impedance receiver, but this is optional. (The only effect of leaving out the tuner is a weaker signal.) The end in the tree was pointed at Jupiter at the time of the recording. The receiver was tuned to 20.473 MHz. The modulation mode was AM.
The signal shows the 2 main characteristics of Jovian decameter radiation - the surf-like static crashes and the staccato beat. The static crashes have a much wider bandwidth than the beat. At the time of the recording, it was possible to tune above and below the beat and still hear the static crashes.
Jovian decameter radiation is inconstant. It comes and goes whenever it feels like it. Sometimes it blasts through almost loud enough to be heard on a crystal set, other times it cannot be heard even by professional radio astronomers. If the signal disappears, try hunting around on different parts of the band. And remember, during periods of high solar activity, ionospheric conditions may prevent reception of any non-terrestrial signals in the decameter band.