[amsat-bb] OSCAR-11 Report

Clive Wallis clive at g3cwv.co.uk
Sat Oct 2 08:54:02 PDT 2010

           OSCAR-11 REPORT   30 September 2010

This report covers the period from 30 March to 30 September
2010. During this time the satellite was silent until it was
heard by JA0CAW on 29 August. Since then, it was heard until
08 September and from 18 to 29 September. Excellent signals
have been reported from stations located around the world,
and good copy obtained from decoded telemetry frames.

There has been a significant change since the previous
period of activity which ended in March 2010.  The on-board
clock is now very stable.  It's gained only three seconds in
30 days. This is comparable with its accuracy when the
satellite was fully operational. During its first 21 years
it gained approximately one minute per year. However, there
is still an accumulated loss of 309 days, which has occurred
during eclipses of the last few years.!

The other change is that it's now transmitting during
eclipses, although signals are weaker at those times. This
indicates that there is still some capacity remaining in the

These two changes suggest that some part of the system may
have recently failed 'open circuit' thus reducing the
overall power drain of the system, and allowing more power
to be available during eclipses.  There was an unexplained
current drain observed when analogue telemetry was last
transmitted. This fault might have cleared. Interestingly,
the status telemetry shows that the Digital Store & Readout
experiment has switched off, since the satellite was
previously heard in February.

The satellite appears to be operating for ten days on,
followed by ten days off, so it should start transmitting
again around 09 October.

The Beacon frequencies are -

VHF 145.826 MHz.  AFSK FM  ASCII Telemetry

UHF 435.025 MHz.  OFF

S-band 2401.5 MHz. OFF

Reception reports have been received from Bernard FY1LE,
Roland DG1EBR, Mike DK3WN, Tetsu JA0CAW, Adam SQ8MFC,
MM0DNX, Tony VK3KKP/G8HIM, Martin DC1MAR, John M0BIC,
Etienne F1GRR and Carlos KD6GRF. Many thanks to everyone.

Many reports have also been added to the live satellite
status page, on the website set up by David KD5QGR and Bob
WB4APR. This is a very convenient and easy to use facility,
which shows the current status of all the amateur
satellites. Strongly recommended for future reports!  The
URL is http://oscar.dcarr.org/index.php

For the benefit of new listeners, here is a short history
of OSCAR-11. It was lauched in 1984, providing telemetry
and other digital services for amateur radio and educational
users. During its many years of operation it survived long
periods of eclipses and continuous full sunlight.

In 2002 the satellite reverted to its default mode of
operation, controlled by the watchdog timer. In 2005 all the
analogue telemetry channels failed. Solar eclipses also
started to cause the watchdog timer cycle to reset, which
switched off the satellite for approximately 15 days.

In 2008 solar eclipses became a permanent feature of every
orbit, causing the satellite to switch off for about 15
days, probably after only one orbit of transmission. Thus
the satellite was not expected to be heard again for any
continuous period until 2019, when there will be some
eclipse free periods. However, the satellite started
transmissions unexpectedly in November 2008. These continued
until March, when it was followed by silence until until the
recent period of activity.

OSCAR-11 transmits on 145.826 MHz., set receiver to NBFM.
The satellite has a characteristic sound, rather like raspy
slow morse code, sending "di di dah dah dah dah dah dah dah"
sent over a period of five seconds. If you are receiving a
very weak signal, switch the receiver to CW or SSB. You
should hear several sidebands around the carrier frequency
and should be able to hear the characteristic 'morse code
like' sound on at least one sideband.

Please note that you need a clean noise-free signal to
decode the signals, and your receiver must be set to NBFM
mode, for a decoder to work.

If you need to know what OSCAR-11 sounds like, there is an
audio clip on my website www.g3cwv.co.uk/ which may be
useful for identification and as a test signal for decoding.

The current status of the satellite, is that all the
analogue telemetry channels, 0 to 59 are zero, ie they have
failed. The status channels 60 to 67 are still working. The
real time clock is showing a large accumulated error, but is
now incrementing accurately to within a few seconds per
month. The day of the month has a bit stuck at 'one' so the
day of the month may show an error of +40 days for some
dates. The time display has switched into 12 hour mode.
Unfortunately, there is no AM/PM indicator, since the time
display format was designed for 24 hour mode.

The spacecraft computer and active attitude control system
have switched OFF, ie. the satellite' attitude is controlled
only by the passive gravity boom gradient, and the satellite
is free to spin at any speed.

The watchdog timer now operates on a 20 day cycle. The
ON/OFF times have tended to be very consistent. The average
of many observations have shown this to be 20.7 days, ie.
10.3 day s ON followed by 10.4 days OFF.

Listeners to OSCAR-11 may be interested in visiting my
website. If you need to know what OSCAR-11 should sound
like, there is a short audio clip for you to hear. The last
telemetry received from the satellite is available for
download. The website contains an archive of news &
telemetry data which is updated from time to time. It also
contains details about using a soundcard or hardware
demodulators for data capture.  There is software for
capturing data, and decoding ASCII telemetry.  The URL is
www.g3cwv.co.uk .

If you place this bulletin on a terrestrial packet network,
please use the bulletin identifier $BID:U2RPT149.CWV, to
prevent duplication.

73 Clive G3CWV   xxxxx at amsat.org (please replace xxxxx by g3cwv)

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