Radio-Jupiter Central

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Jupiter is a wonderful object for radio study. It is somewhat predictable and yet often surprising in its violent outbursts below 40 MHz. You can receive Jupiter using relatively simple equipment or you can construct complex spectrograph receivers and build monstrous antenna arrays to capture its more subtle messages. The complex relationship between the gas giant planet and its volcanic moon Io is not completely understood, but we do know these bodies work together to produce "radio noise storms" as they pirouette through space. Many factors come into play for the amateur radio astronomer who tries to capture a noise storm. In order maximize your chances of success, you should take time to understand the potential hurdles and optimize your equipment for this task.

What frequencies can I use to hear Jupiter?

Jupiter emits radio signals from just below 40 MHz down to a few kilohertz. Actually, the planet may be detected at higher frequencies with very large radiotelescopes, but those emissions are not the ones we are interested in here. The radio noise storms of interest can be heard from about 15 MHz up to a practical limit of about 38 MHz. Below 15 MHz the signals are severely attenuated or refracted away by the Earth's ionosphere. At the upper limit the strength of the signals tapers off rapidly.

The emissions we can hear are often referred to as decametric noise storms, because the waves are tens of meters long. Okay, it is possible to hear Jupiter from 15 to 38 MHz, but what are the optimal frequencies? The consensus seems to be that 18 MHz up to about 28 MHz is a good place to listen. A good rule would be to pick the lowest frequency in this range which was not being hindered by ionospheric refraction.

Unfortunately, during times of high sunspot activity, (the last peak was in 2000), the ionosphere can remain excited all night long. One way to judge if the ionosphere will get in your way is to check a ham band just below where you intend to listen. If you hear amateur radio signals coming in from distant places on the ham band, then you know that the ionosphere is reflective enough that it is bouncing those signals. If the ionosphere can keep the amateur radio signal under its blanket in this way, then it will likely be bouncing away the signals from Jupiter, and you will not hear them. The amount of bending that the ionosphere imparts to a radio wave is inversely proportional to the frequency of the signal. Thus, you can often escape the ionospheric effect by going higher in frequency. Understanding the behavior of the ionosphere is then crucial to your success. You should understand that the ionosphere changes in behavior throughout the day, and is usually much more active while the Sun is above the horizon.

As a practical matter, you will have to pick only as many frequencies to monitor as your equipment will allow. The real limitation is the range of frequencies over which most antennas will operate effectively. A good directive antenna is usually only good for a range of about 500 kHz or so. There are some exceptions, log periodic yagi arrays, and arrays of conical helices are quite broad banded but are not commonly owned by amateurs because of their size. You will probably settle on one or two frequencies and build the best antenna you can for those. 18 MHz and 24 MHz might be good choices.

When will Jupiter be active?

You can't just turn on the radio and expect to hear Jupiter anytime it is above the horizon. Researchers have uncovered definite patterns in the times when Jupiter was most active after assembling many years of observations. They have found that when certain of Jupiter's longitudes are facing Earth, the likelihood of receiving a decametric noise storm is greatly enhanced. Three longitude regions were shown to have this characteristic. They were labeled A, B, and C. As mentioned earlier, the Jovian moon Io is also important and it was found that certain combinations of Jupiter's central meridian longitude (CML), and Io position in its orbit around the planet could be significantly related to noise storm reception. Read more about these different modes here.

There is one more long term factor you should know about, the Jovicentric declination of the Earth.

Radio-Sky provides you with prediction tables for times when the probability of hearing Jupiter will be high. Click here to see these tables. You will also find a convenient program that produces customized predictions for your location, Radio-Jupiter, on the Radio-Sky CDROM.

What role does the Sun play?

As mentioned before, when the Sun is above the horizon the ionosphere is usually more active and prohibits the penetration of Jupiter's signals. When Jupiter and the Sun appear close together in the sky, the likelihood of hearing Jupiter diminishes. Solar noise can also be significant during periods of high sunspot activity, masking Jupiter. If you think about the geometry of our orbits around the Sun, you will realize that when Jupiter appears near the Sun it must be on the far side of its orbit in relation to the Earth and is thus more than twice as far from us as it is when it appears high in the night sky around midnight.

What equipment do I need?

To hear Jupiter you will need a receiver and an antenna. The selection of these is important enough that we have prepared two special pages for you to look at.

Click here for the Jupiter antennas page.

Click here for the Jupiter receivers page.

How can I record Jupiter?

You may want to record Jupiter's sounds for later playback and study. A standard tape recorder will do, but you should use the highest quality available and avoid recorders with automatic gain control which cannot be defeated. Another good option is to record on the audio track of a video tape recorder. In order to keep the VCR tape from dragging and wobbling, you must also supply a video signal. A set up that I have used points the camera to a digital clock and an oscilloscope trace of the audio signal while the audio track records from the Jupiter receiver.

You can record the envelope of the audio signal on a strip chart recorder or on your computer using a sound card and the appropriate software. Radio-SkyPipe software fills this role beautifully. With the Pro version of Radio-SkyPipe you can record wav files on your computer in addition to the charts of the sounds. From such charts the pattern of the storm as a whole can be discerned.

What will it sound like?

Below are links to some sound files of actual Jupiter noise storms. Two types of "bursts" can be heard. The long burst, or "L burst", is reminiscent of waves crashing on a seashore. These bursts are thought to be modulated by the solar wind. A short duration, popping type, burst called an "S burst" is common in certain decametric noise storms. These are result from fairly narrow band noise signals which drop rapidly through the radio spectrum. As the noise energy passes through the narrow band pass of your receiver a pop is heard. You have to be careful not to confuse the decametric noise storms of Jupiter with lightning crashes which are especially common in the summer months. A little practice will make it possible for you to sort out the difference. The lightning crash is distinguished by it's sudden onset.

L Bursts

S Bursts

S Bursts (slowed down 128 times)

Bursts from the 1999 SARA conference

Io B Storm of 09/23/2000

Io B Storm of 11/27/2001 Several charts and sound files. An exciting storm.

Io B Storm of 01/05/2002 chart and sound files of S bursts.

Io B Storm of 03/10/2002 L burst example sound file.

Io B Storm of 03/10/2002 S burst example sound file.

Is there anything I can do about local interference?

If you live in a populated area, you are likely to be victim to any of a thousand sources of local static interference. It doesn't take much interference to mask the subtle signals from Jupiter. If you cannot locate and root out the interference at its source, you can still sometimes prevail by using a noise canceling device. A receiver with a noise blanking circuit is usually quite expensive, but is quite effective in eliminating spike type interference, (and unfortunately, possibly S bursts). Using a directional antenna which has a high rejection in other than the intended direction is helpful. As a last resort you may have to take your equipment somewhere which is not so electromagnetically polluted.

A few words about Project Jove.

The Jove Project is a wonderful new NASA sponsored project designed to get high school students involved with hands-on science. A receiver kit designed by Jupiter researcher Dick Flagg and a dual dipole antenna kit are available for reasonable cost through this project. You do not have to be in high school to get involve with this program. Amateur scientists are welcome. Check out the action at: The Jove Project

Jupiter Links

Radio-Sky Jupiter Noise Storm Predictions

A Panoramic View of the Big Dipole Array at the UFRO

Windward Community College Radio Observatory - Realtime streaming decametric audio and Radio-SkyPipe stripcharts.

Voyager Planetary Science Info (Great for Teachers).

University of Florida Radio Observatory Jupiter sound files and prediction tables.

Advice from the Univ. of Florida about receiving Jupiter.

JPL Radio Observation of Comet Shoemaker-Levy press release.

Another Jupiter recording, and info at a John Kraus site.

Low frequency Jupiter emissions, recorded by the Ulysses probe. Great graphic!

Nancay Jupiter Observatory in France Real-time Spectrographic Display