Date: April 4, 2010
Title: Introduction to the Theory and Practice of Jovian Radio Astronomy
Podcaster: Edgardo Molina
Organization: Pleiades Research and Astronomical Studies A.C. in Mexico City, Mexico – www.pleiades.org.mx (web site soon to be presented also in English)
Description: There is a new way of enjoying the Gas Giant planets. Jovian Radio Astronomy. Those marvelous worlds also give us the opportunity to listen to their radio emissions. You do not have to empty the bank account to build an impressive radio astronomy setup to achieve this. Simple short wave radio equipment tuned for radio astronomy and some knowledge in wire antenna construction and setup, will allow you to integrate a station capable of recording, studying and sharing this information in real time. There is more radio astronomy activity from our Solar System neighborhood than you can imagine.
Bio: Edgardo Molina. B.S. in Mechanical Engineering from the Anahuac University in Mexico City. Post graduate studies in IT Engineering and a Masters Degree in IT Engineering. Working for IPTEL, an IT firm delivering solutions to enterprises since 1998. Space exploration enthusiast who participated in several Mexican space related activities. Licensed amateur radio operator with call sign XE1XUS. Amateur astronomer since childhood and actual founder and president of the Pleiades. Research and Astronomical Studies A.C. in Mexico City, Mexico. Avid visual observer and astrophotography fan. Public reach through education in exact sciences, engineering and astronomy. Lectures and teaching in several universities since 1993.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Bob Moler, an amateur astronomer in northern lower Michigan, and volunteer broadcaster of the week-daily astronomy program, Ephemeris, on Interlochen Public for what will be 35 years this June 1st.
Transcript:
Hello, my name is Edgardo Molina from Pleiades. Research and Astronomical Studies in Mexico City, Mexico. I am your host today for this episode of 365 Days of Astronomy podcast.
Today we are going to explore one fascinating subject on planetary studies. Jovian Radio Astronomy. In short, the study of the radio emission activity from the “Gas Giants.” The strongest emissions come from Jupiter, and so we will be concentrating on that planet. Radio Astronomy as we know it today is not that old. The development of radio equipment technology takes us back to the early 20th century with the works of Mr. Marconi. At that time, telegraph communications were tested to bridge long distances separating the continents. The frequencies used for this type of radio communication was in the order of several meters in wave length, well into the short wave spectrum.
As we currently know, the so called “static” noise at those frequencies often interfere with the radio telecommunication processes. It was Karl Jansky’s job commissioned by the Bell Labs in the USA who found that most of that static noise came from outer space and not from ground sources as it was originally assumed. At that time, there were no formal interests in studying the universe in the radio frequency spectrum. In fact the first radio astronomers were amateur radio operators who had all the means to achieve the initial observations reported by Jansky.
It was discovered during the 1950´s by Burke and Franklin in the USA, that Jupiter emits strong radio signals. Early radio astronomy antennas formed by clustering simple wire dipole antennas were used to detect this emissions. The spectral range of Jupiter emissions stretch from several kilohertz to tens of megahertz. Jupiter radio waves that fall within a frequency range of 300Khz are known as kilometric Jovian radiation or KOM for short. The next range of Jupiter emissions lie in a frequency space between 300Khz and 3Mhz, those are called hectometric Jovian radiation or HOM. Decametric Jovian radiation or emissions within 3Mhz to 40Mhz are called DAM for short. The latter emissions are the most important in terms of being the first to be observed from our planet. They show periodically and so it helped to relate them to planet Jupiter. There is a sub classification of the DAM or decametric radiation, called Io-Jupiter system, which is related to the interaction of Jupiter and it´s moon Io. Within this subclassification lies the strongest part of the DAM emission.
All of these emissions are produced by a phenomenon called Cyclotron Maser Instability, originating at the polar regions, where a strong flux of electrons bounce between poles. This electron flux carry electrical current from the polar regions of Jupiter to the magnetodisk, or the zone where all the magnetic field of Jupiter is concentrated, in a flat like disk equivalent to the tear drop shaped Earth’s magnetic field.
The intensity of Jupiter radio emissions is variable in time. There are however strong transient emissions which burst occasionally. These bursts are known as “S Bursts” and are more powerful than the rest of the radio emission components. To have an idea of how powerful the DAM emissions are, lets compare them symbolically to a common earthbound FM broadcast radio station which emits around 150KW of radio power into space. The DAM emissions are about 100GW in power. That is several orders of magnitude! Kilo vs. Giga (hundreds of Watts vs. thousands of millions of Watts). It is important to point out that the HOM and KOM emissions are less powerful, in the order of 10GW. There are shorter wave lenght Jupiter emissions, in the decimeter wave length range, so called DIM for short. But for the practicality of the coming experiments they are harder to detect. That is the reasson why the DAM emissions are so studied and will be the main subject of our practical part of the podcast.
Being Jupiter a strong radio source as previously stated and emitting mainly in the decametric bands, we have the opportunity to do some basic Jupiter Radio Astronomy, from home or from anywhere our paths led us on planet Earth. Nowadays there are several excellent programs for signal analysis on the Internet, most of them are shareware or freeware so if there is a cost for them it is purely symbolic.
We will also need an antenna, it does not have to be fancy. We will be OK visiting the local hardware store and buying some electrical single pole insulated wire and a couple of electrical insulators which can be constructed from any piece of plastic or strong electrical insulating material. Towers, regular TV antenna supports or telescoping poles will be enough for supporting our antenna. The most “difficult” part of the project is building or getting our hands on a decent short wave receiver. Nowadays there are plenty of second hand short wave radio receivers on eBay. As Jupiter radio emissions take place below 40Mhz, most any short wave radio with simple modifications or maintenance will work. It is important to choose a high frequency in the range of 15Mhz to 40Mhz, due to the fact that below those frequencies the Earth’s ionosphere will act like a shield for man made signals and will bounce them back to the ground to further complicate the reception of Jupiter emissions. One band that has appealed to me in the past is the one around 20Mhz. I listen on the upper limit of the 15m band with amateur radio equipment, just above this mark at 21Mhz. There is also an excellent site on NASA servers called Jovian Radio Astronomy, where you can find kits for building a receiver from scratch. You can Google “Jovian Radio Astronomy” for the exact URL.
I must emphasize the need of a good computer setup, either desktop or portable. This opens the window to do fixed and mobile Jovian Radio Astronomy. The only requirement for the computer is to have a recent sound card to be used as an analogue to digital converter when feeding the signal from our radio to it. Windows? Linux? MAC OSX? Your choice of operating system. There are programs written for most of the current operating systems on the market. However if you need some advise to decide I can give you some hints. Linux, the most stable O.S., MAC very simple to use, Windows, the one with the most software available but with the well known stability issues. You simply can not go wrong with any choice. I like the idea of the new affordable and compact netbook computers, they have an integrated sound card capable of doing the job.
Now to the setup of every piece of equipment. The dipole antenna is an afternoon project for most people. One can be built in less than ten minutes by experienced hands. The particulars for building a dipole wire antenna can be found at several sites on the Internet, please kindly also Google for that. The antenna should be connected to a coax feed line, 50 Ohm impedance type RG8 for fixed long cable runs or the cheap RG58 for portable operation or short cable runs. Standard VHF PL259 male type connectors on each end of the feed line. Please take good care of the position of the dipole antenna. Due to the fact that it is a fixed non steerable antenna, it should be oriented length wise in a north-south direction. That way the antenna main radiation lobes will be able to pick Jupiter rising in the east, crossing the local meridian and setting finally to the west. The height of the antenna above the ground is also important, as the radiation pattern will me affected by the ground effect. The antenna is recommended to be placed at 3 meters above the ground. Be sure the antenna is located in what radio engineering calls “free space”, which is a desirable and theoretical location far away from large metal structures, automobiles, electrical motors and all sorts of radio interfering equipment. Special care should be taken with the soldering iron while using it for the antenna construction, all solder joints should be hot enough to avoid false contacts and the possibility of picking up man made noise through them. This is true at both the antenna and coax feed line.
The radio used for this application should provide a control for the audio frequency gain and also should provide control over radio frequency gain and the use of audio filters. We want the radio to be able to pick all the radio frequency signal it can get without any distortion caused by the radio settings or capabilities. There are a lot of amateur radios out there, be sure to pick one for the High Frequency spectrum and one that works on the 21Mhz/15m band. There is no considerable effect if the radio operates from vaccum tubes or if it is a digital assisted unit. This way you can pick up a radio according to your specific budget. Now a hint. If you ever want to get started in amateur radio, consider that radio as an investment that will allow you to explore another interesting hobby that gave birth to modern Radio Astronomy.
If you can get an external good sound quality speaker monitor, this will allow you to hear the audio signals if working from a permanent location. Remember the use of a “Y” audio splitter and do not worry too much for stereophonic connectors on the speaker as the radio will only provide a monophonic output. If you like to work without disturbing others with static noise, consider the use of a good pair of headphones. Open air headphones instead of the closed ear plug type are recommended. Do not worry too much for the headphone quality, remember that you will be using them for monophonic listening. A good choice should not distort the sound. Please mind the volume levels as you can hear transients without notice and injure your hearing.
I will mention some possibilities in terms of software. I will focus on Windows software as the majority of computers out there rely on this operating system. We have the following programs:
Radio Sky Pipe Pro: This program allows you to graph the Jupiter radio emission on a signal strength vs time plot. The program also allows for sharing this information via the Internet with other observatories.
Radio Jupiter Pro 3: This program will allow you to plan ahead your Jupiter observations and decide when it is the best time to look for Jupiter radio storms. It is full of other features that will come handy during your studies.
In the case of the Radio Sky Pipe Pro software, one can use a dedicated computer as a server in order to gather the audio data on the hard disk and then plot it on a graph, showing all the aspects of the radio emission behavior. Considering that today’s computers have plenty of disk space for this and other enterprises, there is no need to consider any other form of signal recording.
Jupiter emissions in general, resemble a peaceful beach with waves hitting the shore, some others are just spiky transients of powerful energy that stand out of the background noise. There are numerous audio examples in the Internet if you look carefully for them, you will notice the differences. While listening please note that the long duration emissions are called “L” bursts, the letter L stands for Long duration events. The rapid fire emissions are called “S” bursts and the letter S stands for Short duration events.
There is a lot of information on Jovian Radio Astronomy on the net. This podcastʼs intention is only to introduce you to the subject. Please allow yourself time to do some research and enjoy this interesting part of Radio Astronomy. I am sure that you will see the universe differently from what you con expect from a traditional telescope view.
For the 365 Days of Astronomy podcast this is Edgardo Molina from Pleiades. Research and Astronomical Studies in Mexico City, Mexico, wishing you clear radio frequency skies. Our web page can be found at www.pleiades.org.mx, there our contact information is waiting for your kind comments. Thank you for listening.
End of podcast:
365 Days of Astronomy
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