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Spring 2004 Issue |
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The Flight of
As amateur radio
ballooning reaches its
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 Launching an NSTAR mission. The balloon is held by two lanyards which go through a metal ring at the balloon’s neck. This suspends the payloads off the ground for a smoother launch, yet keeps the balloon under control. |
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It’s a quiet October morning in western Iowa—clear skies, a little fog over some of the rivers and creeks, and a light frost covering some of the freshly harvested fields. It’s not quite sunrise yet, but the orange glow in the eastern sky promises us that dawn is coming soon. On this morning the members of Nebraska Stratospheric Amateur Radio organization (NSTAR) are en route to a small farm about 15 minutes east of Council Bluffs, Iowa. Before the completion of this day, our adventure will take us into the upper reaches of that sky, by way of the upper atmosphere via an unmanned balloon. Radios and balloons have been used in tandem to explore the atmosphere for about 75 years. The earliest flights date back to the 1920s, when relatively crude radios and instruments were attached to unmanned balloons. These balloons were released so that measurements could be made at high altitudes without the need for an airplane to carry the equipment. By 1937, the U.S. Weather Bureau had a network of stations making regular weather observations using radiosondes to observe temperature, pressure, and humidity to altitudes of 100,000 feet or more. This practice continues today with about 70 National Weather Service stations in the conterminous U.S. launching radiosondes with weather balloons twice per day. The first known amateur radio flight was in 1979, when a Canadian amateur radio club sent its radio equipment to high altitude as a radio propagation experiment. Eight years later, Bill Brown, WB8ELK, launched an ATV (amateur television) payload over Ohio to beam back pictures from altitudes high enough to show the blackness of space. Since that time, the advent of low-cost, lightweight GPS (Global Positioning System) receivers and microprocessors has opened the hobby to the inclusion of even more capable payloads containing repeaters, still cameras, camcorders, SSTV (slow-scan TV) transmitters, and a wide variety of scientific experiments. The data from the GPS receiver is transmitted to the ground via packet radio, where it is decoded and plotted using APRS (Automatic Position Reporting System) to an accuracy within 50 feet. This real-time tracking information of our equipment lets us fly our equipment to an altitude of 20 miles or more and be blown downwind over 100 miles. As a result of our ability track our balloons, we have a high degree of confidence that we will recover everything after the flight’s completion. Normally, VHF or UHF FM terrestrial propagation is limited to a few tens of miles at best. Sometimes atmospheric conditions such as an inversion allow further propagation if the weather is right. With the high altitudes achieved by balloons, direct reception of FM signals such as packet is possible over great distances, even with power level coming from an HT (handi-talkie, 5 watts or less). At 100,000 feet the direct line of sight is over 400 miles. In 2002 an APRS packet transmitted on the 2-meter ham band from an NSTAR payload over Iowa was received 440 miles away by a station in Norman, Oklahoma.
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