[amsat-bb] AO-7 Recent Behavior

Paul Stoetzer n8hm at arrl.net
Sun May 25 20:49:22 UTC 2014

Good morning,

AO-7 seems to be showing some odd behavior. For about three weeks of the
eclipse cycle, it had been operating perfectly in Mode B with strong and
clear signals on each and every pass. However, yesterday it was off during
two ascending passes over the United States. It was back in Mode B during a
pass over the Western United States around 23:30Z last night.

PY5LF reported that it was in Mode B for 5-6 minutes after leaving eclipse
and then it abruptly shut off. Reports from Europe on the AAR29 log also
indicate it had shut off on ascending passes.

My theory is that the sun angles on the solar panels are not ideal at this
point. When it powers up after eclipse in Mode B, voltages fall such that
the undervoltage detector kicks in and switches the satellite to Mode D
(both transponders off). The satellite would then stay in Mode D until it
loses power on the next eclipse and restarts in Mode B. If this is the
case, my recommendation to Southern Hemisphere stations would be to wait a
couple of minutes after it comes out of eclipse to start uplinking to the
satellite and to keep power levels low until the panels are better

This behavior has not been reported on descending passes, though signals
were reported to be weak and distorted at times this morning over the
United States. Weak and distorted signals on the two meter downlink may be
partially explained by Sporadic E as six meters has been open most of the


Paul, N8HM

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