Recommendations for identifying and observing the Jovian Decametric Emission.

When to observe the decametric emission

  • The best times for observing Jupiter are at night, between 10 PM and 7 AM local times when the ionosphere is more transparent for low frequency signals coming from space. This also translates into better observing conditions with less radio stations and interference reflecting off the ionosphere.

  • It is highly recommended that you try to observe during predicted Io-related storms. The probabilities of detecting the emission are higher during those periods. Check the prediction tables and choose an observing period coinciding with an Io-related storm. In the prediction tables the Io-related storms are labeled as Io-B, Io-A, and Io-C.

  • Make sure that the planet will be in the beam of your antenna when the predicted storms will occur or that you will be able to point the antenna to Jupiter when the storm occurs.

  • Don't try to observe Jupiter when the planet is outside the beam of the antenna. If you are using an antenna with a fixed beam, donít try to observe when Jupiter is too far from transit.

  • Keep the receiver tuned at a clear spot near the center of the band. If you start getting a station tune a few kHz away from the station. There is no need to go up and down the dial searching for Jupiterís emission. The emission is wideband and can be received anywhere in the receiverís band.

  If you think that you are hearing Jupiter

  • Tune the receiver near the center frequency of the band. If you begin receiving emission, tune a few kHz away by turning the tuning knob a few degrees. Keep it there for at least 10-20 seconds and watch to see if you continue receiving the emission. If you don't get deflections, it was probably just a station. If you continue getting deflections, tune to the opposite side of the center frequency and wait there for another 10-20 seconds. If you continue getting deflections, it is probably Jupiter. Jupiter's emission is generally wide band. The bandwidth of the emission can be from a few hundred kHz to a few MHz. Remember that Jupiter emits two main types of bursts; they are the L and S bursts. If at any point you hear voices, music, or Morse code, periodic modulation, or other types of modulation, those are just plain terrestrial interference.

  • Also remember that the Jovian radio emission is not a steady hiss or sound. Its intensity is modulated by scintillation in the terrestrial ionosphere and in the electron content of the interplanetary medium

Keeping a logbook of the observation.

  • It is a good practice to keep a log of your observation. You may want to report your observation to a group collecting data for a research project or just tell somebody about what you have observed.

  • Record the time at which the observation begins and ends.

  • During the observation constantly listen to the receiver's audio output. Identify Jupiter and interference. If Jupiter is heard, record the time and the type of emission (L or S bursts).

  • If possible, during periods of interference or if interference is mixed with Jupiter pulses, record the times and type of interference. Be brief when recording interference; you donít want to waist too much time documenting interference. Just one word may be enough such as station, static, lightning crash, pop, buzz.

  • Record any problem experienced with the equipment. Some of the most common problems are changes in gain in the receiver, unstable output, and saturation of the receiver by powerful stations. This may help in identifying periods in which the validity of the observation is questionable

  Types of Interference

Several types of interference are commonly heard during an observation. The following is a short list and description of some of the common types

Stations : There are many types of stations, voice, telegraphic (Morse code), telex, sweeper (some are ionospheric sounding stations), CW or continuous wave (no modulation). Stations are narrow band; usually they disappear if one tunes a few kHz away.

Lightning crashes: Local lightning crashes are usually strong. They last for a second or less. Under some circumstances the ionosphere may reflect distant lightning crashes. They are usually weaker and occasionally they may sound like S bursts. Lightning crashes are wide band; they don't disappear by tuning the receiver to a different frequency.

Buzz: It originates in coronal discharges from power lines and insulators. It is wide band and can be easily identified by its characteristic 120 Hz sound.

Pops: Usually generated from power line transient. Are the result of the sudden connection or disconnection of electric appliances and electric motors. Common sources of pops are water pumps, air conditioners, and refrigerators

Things to keep in mind

  • The observer is the only one that can identify a deflection. After the observation, nobody will be able to tell what caused a deflection. It is impossible to determine the origin of a deflection just by examining a chart record. It is necessary to have additional information like sound.

  • An audiotape or a file from an observation for which there is no written record of what is in it, is of little use. DO NOT trust your memory.

  • Based on past experience, new observers tend to identify as Jupiter almost any sound or deflection. If you are not familiar with Jupiterís sounds, interference, and solar bursts, go to the UFRO online web site and listen to them. Don't consider yourself an experienced observer after having logged just few hours of observation.

  • If you want to record the audio output of the receiver into a tape recorder, run some tests before doing the actual recording. Make sure that the audio output for the galactic level is not too high. If the level is too high, even small Jupiter deflections will saturate the input of the tape recorder and the signal will be badly compressed or clipped.

  • If you have access to a stereo cassette recorder or a cassette deck, you can record Jupiter signals in one channel and timing information in the other. WWV station is a good source of timing signals. If you have a short wave receiver you can tune to WWV on 5, 10, 15, and 20 MHz. During the night, only the lower frequencies are usually heard.

  • If there is an approaching lightning storm while you are observing, disconnect the antenna and shut down all your equipment; even better, unplug the equipment. Lightning can strike your antenna or the power lines and damage the receiving equipment and what is even worse, seriously injure the observer.