[amsat-bb] AO-7 Recent Behavior

Paul Stoetzer n8hm at arrl.net
Tue May 27 00:58:09 UTC 2014

AO-7 apparently switched to Mode D around 1945Z on a pass over the western
Atlantic Ocean. Signals were a bit weaker than normal and started to FM
shortly before it switched off as the noise floor of the transponder was
modulated by a strong CW signal in the passband.

Please remember to limit your power output to 100W ERP. This may be
especially critical during this time period to prevent the satellite from
switching off.

Reports are greatly appreciated.


Paul, N8HM

On Sun, May 25, 2014 at 2:42 PM, PY5LF <py5lf at falautomation.com.br> wrote:

> Paul
> On this pass , finishing 18:43UTC ,  AO7 works all the time !
> 73
> Luciano Fabricio
> Curitiba-PR-BR GG54jm
> http://www.qrz.com/db/PY5LF
> -----Mensagem original-----
> De: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] Em nome
> de Paul Stoetzer
> Enviada em: domingo, 25 de maio de 2014 12:49
> Para: amsat-bb at amsat.org
> Assunto: [amsat-bb] AO-7 Recent Behavior
> 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 illuminated.
> 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
> morning.
> 73,
> Paul, N8HM
> _______________________________________________
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb

More information about the AMSAT-BB mailing list