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Jon Wallace

111 Birden St., Torrington, CT 06790,jwallace@snet.net

Amateur RadioAstronomy Projects

The author participated in a variety of activities during theInternational Year of Astronomy in 2009.

As my IYA 2009 (International Year

o Astronomy) activities come to a close, Iwould like to share some o my avorite radioastronomy projects with you in the hope thatyou will enjoy them as much as I have.

I am a science teacher in Connecticut.I have long thought that too much stress isplaced on visual science, and Ive alwaystried to expose students to non-visual experi-ences. With this in mind, I started exploringradio astronomy in the early 80s and joinedthe Society o Amateur Radio Astronomers(SARA). I got lots o help building projectsand have been at it ever since (check outSARA at radio-astronomy.org).

The rst project I will discuss, a solarradio in the VLF range, is one I started manyyears ago. It is very simple and yet yieldsdata that can be reported to a national orga-nization and is used to do real science! Itstudies the reaction o Earths ionosphere tosolar activity by measuring the intensity oa received signal. These radios are knownas SID (Sudden Ionospheric Disturbance)monitors, since they are measuring thechanges in intensity o a radio signal dueto ionospheric disturbance caused by solarfare activity.

IonosphereThis region o the atmosphere is ionized

by solar and cosmic radiation. It ranges rom70 to 1000 km (about 40 to 600 miles) aboveEarths surace, and is generally consideredto be made up o three regions D, E, andF. Some also include a C region and mostexperts split the F region into two (F1 andF2) during the daylight hours. Ionization isstrongest in the upper F region and weakestin the lower D region, which basically existsonly during daylight hours. This is becausethe number o ree electrons increases as

Figure 1 Earths atmoshphere, including regions o the ionosphere.

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you rise through the atmosphere, reachingradio signicance at about 70 km. You also

have lower pressure at higher elevation.These conditions lead to the production omore monatomic gases and ionization thatlasts longer because o the distance betweenatoms/molecules. Most o the ionization weare discussing is due to ultraviolet light, butat lower altitudes X-rays are needed to pro-duce the ionization seen. Figure 1 is an illus-tration o the Earths atmosphere, includingthe ionosphere.

Solar FlaresFlares are enormous explosions that

occur near sunspots on the surace o thesun, lasting roughly an hour and heating theregion to millions o kelvins. See Figure 2.Most astronomers believe these events arecaused by the suns magnetic eld. Sincethe sun is a fuid, magnetic eld lines canget twisted. Near sunspots, the eld lines getso twisted and sheared that they cross andrecombine releasing an explosive burst oenergy that can travel tens o thousands omiles o the surace o the sun. Obviously,as this energy makes its way to Earth, ioniza-tion in the atmosphere is greatly enhanced.

Flares are thus closely tied to the 11 yearsunspot cycle. The sunspot cycle relates to

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a solar magnetic cycle, which runs or 22 years. During the rst11 years, sunspot requency increases to a maximum and thendecreases. At this point the magnetic poles fip polarity and thecycle begins again or the next 11 years. We are currently comingout o the Cycle 23 minimum and some sunspots rom Cycle 24have been detected. Figure 3 shows how the positions o sunspotson the Suns surace create a butterfy pattern, with 12 sunspotcycles represented.

Flares that can be detected with VLF radios are generallycaused by X-ray fares and have various fux levels associated withthem. Figure 4 explains the classication o these fares.

The fares we can detect with VLF radios are C, M and X. Cfares and below are airly weak disturbances, with little eect oncommunications. M fares are medium sized fares that can causeshort periods o radio blackout and minor radiation storms. Xfares are large events that cause major planetary blackouts andradiation storms. When Im not sure whether or not Ive detecteda fare, I always check The Solar Events Report at the NOAASpace Weather Prediction Center (www.swpc.noaa.gov/ftp-menu/indices/events.html). Here they list events by day and time,which allows you to check your results.

VLF and the IonosphereDuring the daylight hours, VLF signals generally pass through

the D region and are reracted by (or refect o) the E region, thusleading to a weakened signal. During a fare event, the D region isstrengthened and acts as a wave guide or VLF signals, since thewavelength o the signal we are monitoring is a signicant part o

Figure 2 A large solar are, as shown atwww.suntrek.org/images/big-solar-are.jpg.

Figure 3 This graph o multiple sunpot cycles shows how the positions o the sunspots move rom thepolar regions towards the equator as the cycle progresses. This creates a buttery pattern. The image is

rom http://upload.wikimedia.org/wikipedia/commons/9/93/Sunspot_buttery_with_graph.jpg.

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the height o the D region. (Remember that= c / , thus 300,000 (km/s) / 20,000 Hz =15 km). In addition, the signal reracts in theD region now, and less loss is experiencedsince it no longer passes through the D regionto reract in the E region. This generally leadsto a sudden increase in VLF signal, calledSID (Sudden Ionospheric Disturbance).Sometimes the VLF signal could be reduced

(as with my particular VLF radio) becausethe low reractions have more collisions owaves and this leads to increased destructiveintererence.

A quick way to check the perormanceo your VLF radio is to monitor sunrise and/or sunset. Remembering that the D region

X-Ray Flare Classes

Rank o a are based on its X-rayenergy output. Flares are classifed bythe order o magnitude o the peak burstintensity (I) measured at the earth in the

1 to 8 angstrom band as ollows:

Class (in Watt/sq meter)

B I < 1.0 106

C 1.0 106

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Figure 7 This photo shows my completesystem, with the loop antenna at top let, acomputer on a shel and the VLF radio andanalog to digital converter device in a box

below the computer.

Figure 8 Here is a photo o the antenna feld or station NAA in Cutler, Maine.

Figure 9 This schematic is the ADC device rom Jim Sky at his Radio Sky Web site: www.radiosky.com/skypipehelp/skypipe8channelADC.html.

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Figure 10 Here is a close-up photo with my VLF radio on the let and the ADC device onthe right.

Stanord Radio - By Bill and Melinda Lord (SARA)Tim Huynh o Stanord University has designed a simple system to monitor

Sudden Ionospheric Disturbances (SID). He uses a preamp that eeds a signalinto a sound card, which records at up to 96 kHz to collect data at very lowrequencies. The preamp is connected to a one meter loop antenna made o400 eet o solid copper wire. The sotware can be easily confgured to monitormultiple requencies. Commonly monitored requencies used in the US rangerom 21.4 kHz to 25.2 kHz. The unit can monitor rom 7.5 kHz to 43.7 kHz.

Since the system can collect several requencies, the antenna is not tuned.The early designs required an 8 oot loop antenna made o 720 eet o solid cop-per wire, but the current design works with a compact one meter antenna. Youcan increase the sensitivity with a larger antenna i you wish. Stanord is produc-ing 100 units with the assistance o the Society o Amateur Radio Astronomers(SARA) and will be distributing them to schools all over the world.

used an IC socket so I wouldnt be solder-ing the IC directly; construction was veryast and easy. I used an antenna design romMike Hill A Tuned Indoor Loop. SeeFigure 6. It is easy to make but consists o125 turns o magnet wire! Keeping count canbe a challenge. The wire is wound arounda small rame (I made mine out o wood).This is an easy project, well within the skills

o any ham. Figure 7 shows my completereceiving system.Another very interesting monitor is

available rom Stanord University orabout $270 (nova.stanford.edu/~vlf/IHY_Test/pmwiki/pmwiki.php?n=Main.HomePage). It uses multiple requencies tomonitor fare activity. I have included a shortsummary at the end o this article.

TuningI ound that using a coil o wire attached

to a signal generator set to the station re-quency (24.0 kHz or Cutler Maine) pro-vided a great tuning device. Simply turning

the potentiometer or gain and then tuningthe radio, searching or the peak voltage out-put, made short work o it.

NAAThe NAA transmitter is located in Cutler

Maine, and is maintained by the Navy orcommunication with submarines. It oper-ates at 24.0 kHz and has a sister stationat 24.8 kHz called NLK in Jim Creek,Washington. The NAA station occupies3,000 acres and used 90,000 cubic yards oconcrete and 15,000 tons o steel in its con-struction. It produces a 2 MW signal. The

antenna consists o 13 towers, the center

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Figure 11 This graph represents data collected on a quiet day,when no ares occurred.

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Figure 12 This graph shows a day with several large solarares. Also notice the peaks at both ends o the graph,

representing the sunrise/sunset eect.

Figure 13 This graph is rom a day that had an amazingX 14.4 are.

at 980 eet above ground, the next six at 875 eet and the last six at800 eet. The antenna consists o 75 miles o 1 inch phosphor bronzewire above ground. See Figure 8 or a picture I took on a recent visit.

Data Recording/ChartsI record my data through an analog to digital converter (ADC) I

built using plans at Jim Skys Web site (www.radiosky.com/skyp-ipehelp/skypipe8channelADC.html). The schematic is shown inFigure 9. It is a simple device that allows you to gather data throughthe printer port o any computer using Jims sotware called Radio-

SkyPipe. Figure 10 is a photo o my receiver and the ADC in separateproject boxes. I use an old laptop with Windows 3.1. I then export thedata to foppy disk and bring it to my main computer and make thenal charts in MicrosotExcel. In Figure 11, a quiet day with no farespresent is shown. Note the peaks on both ends the sunrise/sunseteect. Figure 12 shows a day with several large fares. Flares usuallyappear as upward peaks, but on my receiver they appear as downwardtroughs. These are M1.6 and M2.3 fares respectively. Figure 13shows a day with an amazing X 14.4 fare! Data can be reported eachmonth to AAVSO through a simple log program, in which you enterthe date and begin, peak and end times o each fare.

ConclusionI hope you will try this simple radio and send your results to

AAVSO. I you have any questions, comments or concerns, eel reeto contact me.

Jon Wallace is a long-time ARRL Associate Member.

For urther inormation check out:

Society o Amateur Radio Astronomers (SARA) www.radio-astronomy.org/

AAVSO www.aavso.org/observing/programs/solar/sid.shtml

Stanords SID Program solar-center.stanord.edu/SID/sidmoni-tor/

Ian Poole, G3YWX, Radio Propagation Principles & Practice,available rom your local ARRL dealer or rom the ARRL Bookstore.Telephone toll ree in the US: 888-277-5289, or call 860-594-0355,

ax 860-594-0303; www.arrl.org/shop; pubsales@arrl.org.