ARLA/CLUSTER: Venerable AO-7 Satellite Approaching a Return to Full Solar Illumination

[Vitor Reis]

AMSAT-OSCAR 7 (AO-7), the oldest amateur radio satellite still in 
operation, is nearing a return to full illumination by the sun, which 
should take place around September 25 and continue until around December 
26. AMSAT’s vice president of operations Drew Glasbrenner, KO4MA, says that 
during this period, AO-7 likely will switch between modes A (2 meters up/10 
meters down) and B (70 centimeters up/2 meters down) every 24 hours. He 
reminded users to use only the minimum necessary power and to avoid 
“ditting” to find their signals in the passband, which can bounce the 
entire passband up and down and sometimes even cause the transponder to 
reset to mode A.

“Try to find yourself with very low power, or on SSB, or best, with full 
Doppler control,” Glasbrenner said. “If you have to use high power to find 
yourself, your receive antenna and system probably needs improvement.”

Last May, the nearly 46-year-old AO-7 made possible a contact between 
Argentina and South Africa — a distance of more than 4,300 miles. Both 
stations were aiming just 2° or 3° above the horizon. AO-7 only works when 
it’s receiving direct sunlight and shuts down when in eclipse.

Launched in 1974, AO-7 surprised the amateur satellite community by 
suddenly coming back to life in 2002 after being dormant for nearly 30 
years and periodically re-emerging. AMSAT considers AO-7 
“semi-operational.” Theory is that AO-7 initially went dark after several 
years of operation when a battery shorted, and it returned to operation 
when the short circuit opened. With no working batteries, AO-7 now only 
functions when it’s receiving direct sunlight, and it shuts down when in 
eclipse.

Built by a multinational team under AMSAT’s direction, AO-7 carries a 
non-inverting Mode A transponder (145.850 – 950 MHz up/29.400 – 500 MHz 
down) and an inverting Mode B (432.180 – 120 MHz up/145.920 – 980 MHz down) 
linear transponder. It has beacons on 29.502 and 145.975 MHz, used in 
conjunction with Mode A and Mode B/C (low-power mode B), respectively. A 
435.100 MHz beacon has an intermittent problem, switching between 400 mW 
and 10 mW.

Source:ARRL

73 de CT2IAG
Vitor