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AO-7 'Zombie' Satellite Again Enjoying its Time in the Sun:

from The ARRL Letter on August 8, 2013
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AO-7 'Zombie' Satellite Again Enjoying its Time in the Sun:

It's baaaaack! Launched November 15, 1974 as the second AMSAT Phase 2 ham satellite, AO-7 may be the zombie of the Amateur Radio satellite world, having returned from the dead more than a decade ago, then periodically re-emerging. Next year, it will be 40 years old, ancient in satellite years. After its batteries succumbed to old age, AO-7 went silent in 1981, only to spring back to life in 2002, although some believe it may have resurrected itself as much as a year earlier. AMSAT describes the Mode A/B bird as "semi-operational" and "almost certainly" running solely from its solar panels. The ham satellite organization theorizes that AO-7's batteries shorted when they failed, but the short circuit subsequently opened, allowing the satellite to return to life. This means AO-7 only works when it's receiving direct sunlight and shuts down when in eclipse. Since the satellite became undead, terrestrial users have enjoyed numerous contacts via AO-7.

"AO-7 is alive and doing okay," satellite observer Frank Griffin, K4FEG, reported this week. "This season's eclipse cycle has ended." Griffin explained that the eclipse period, during which AO-7 falls silent, lasts about 9 weeks, from mid-spring to mid-summer. According to its operating plan, AO-7 switches to Mode B (70 centimeters up/2 meters down) at 0000 UTC.

"The satellite has started its mode switches, but it has not quite settled back down yet," Griffin told ARRL. For example, he said, AO-7 was in Mode A at 1230 UTC on August 5, but had been reported in Mode B earlier. He suspects that even though the satellite is now in sunlight, its orientation to the sun may still affect electrical power onboard the satellite "until it gets a little further into the full illumination." This, in turn, could degrade the transponder performance.

AO-7 has beacons on 29.502 MHz (used in conjunction with Mode A) and 145.972 MHz (used in conjunction with Mode B and Mode C -- low power Mode B). The 435.100 MHz beacon has an intermittent problem, switching between 400 mW and 10 mW.

Potential AO-7 users are advised that due to changes in Amateur Service and Amateur Satellite Service rules, the legality of transmitting to AO-7 on its Mode B uplink is questionable, since that frequency no longer falls within an Amateur Satellite Service allocation. 97.207(c)(2) and 97.209(b)(2) of the FCC rules authorize space station and earth station operation only in the 435-438 MHz segment, and it's unclear whether a 1974 FCC waiver might still cover operation on the original Mode B uplink frequency. -- Thanks to Frank Griffin, K4FEG; AMSAT News Service; AMSAT


The ARRL Letter

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