AO-27 transmits with a power output of 0.5 W into a quarter-wavelength whip antenna. Satellites are approximately 500 miles (800 km) distant when directly overhead and over 2,000 miles (3,200 km) distant when near the horizon. For use on AO-27 with a half-wavelength whip, your receiver sensitivity at 436 MHz should be at least 0.18 uV for 12 dB SINAD, which corresponds to the approximate signal strength of AO-27 at 10 degrees elevation when your whip antenna is correctly positioned for the polarization of the incoming signal. At the horizon, AO-27’s signal strength, under similar conditions, is approximately 0.13 uV. Most modern, high-quality amateur radio transceivers will meet these specifications if designed to operate at this frequency (i.e., without modifications). Most scanners, and most radios which have had to be modified to cover 436 MHz, will not.
AO-27 transmits FM on about 436.795 MHz, plus/minus Doppler shift of up to 10 kHz on either side. Their uplink frequency is 145.850 MHz, plus/minus Doppler corrections of up to approximately 3.4 kHz.
by Ray Soifer, W2RS
AMSAT is a worldwide group of Amateur Radio Operators (Hams) who share an active interest in building, launching and then communicating with each other through non-commercial Amateur Radio satellites. By any measure, AMSAT’s track record has been impressive. Since its founding 25 years ago, AMSAT has used predominantly volunteer labor and donated resources to design, construct, and, with the added assistance of international government and commercial agencies, successfully launch, over 30 Amateur Radio satellites into Earth orbit. Today, almost 20 of these satellites are operational.
The Radio Amateur Satellite Corporation (as AMSAT is officially known) was formed in 1969 as a not-for-profit, 501(c)(3) educational organization chartered in the District of Columbia. Its aim is to foster Amateur Radio’s participation in space research and communication. Since that time, other like-minded groups throughout the world have formed to pursue the same goals. Many of these groups share the “AMSAT” name. While the affiliations between the various groups are not formal, they do cooperate very closely with one another. For example, international teams of AMSAT volunteers are often formed to help build each other’s space hardware, or to help launch and control each other’s satellites.
Since the very first OSCAR satellites (OSCAR stands for Orbiting Satellite Carrying Amateur Radio) were launched in the early 1960s, AMSAT’s international volunteers, often working quite literally in their basements and garages, have pioneered a wide variety of new communications technologies that are now taken for granted in the world’s satellite marketplace. These breakthroughs have included some of the very first satellite voice transponders as well as highly advanced digital “store-and-forward” messaging transponder techniques. All of these accomplishments have been achieved through close cooperation with international space agencies which often have provided launch opportunities at significantly reduced costs in return for AMSAT’s technical assistance in developing new ways to launch paying customers. Spacecraft design, development and construction has also occurred in a fiscal environment of individual AMSAT member donations, thousands of hours of volunteer effort, and the creative use of leftover materials donated from aerospace industries worldwide.
Published on Apr 27, 2012 by Michael Haman