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OSCAR-11 Report




                OSCAR-11 REPORT    23 July 2003


During the period 01 July to 22 July 2003 the 145.826 MHz. beacon has been
heard transmitting continuous ASCII telemetry from 12 July to 21 July.
During this period signals of variable quality have been received. Poor
quality signals may have been caused by the combined effect of poor
satellite attitude, low battery voltage, local interference (QRN) and
packet QRM on the channel. Telemetry transmissions are expected to resume
around 01 August for about 9 - 10 days.

The internal temperatures have increased slightly, indicating that the
maximum eclipse times may have been reached.  The temperatures are now
-0.2C, -1.6C, and +5.4C respectively, for battery, telemetry electronics
and command decoder, respectively. However, there is a considerable
variation in the temperature changes between the three units. This may due
to the very low spin rate producing uneven heating. Temperatures are
expected to increase, reaching a peak in the Autumn with higher
temperatures than in 2002.

The battery voltage observed during daylight passes has increased.
Observations have varied between 13.8 and 12.7 volts, with an average
value of 13.6 volts.

Examination of the magnetometer telemetry shows that the satellite is now
rotating very slowly ie. the spin period is very long. Accurate
determination of the spin period is very difficult when the spin period
exceeds the time of a pass. An approximate period of 1300 seconds was
measured on one occassion, and on another it was impossible to measure the
spin. The direction of rotation appears to have reversed, since the last
report, ie. back to the normal direction.  The slow spin rate has also
caused some uneven heating of the external surfaces, and temperatures of
40C and down to -23C have been observed.

Users of OSCAR-11 should note that the date in the telemetry is advanced by
three days.  The time is advanced by 18.6 minutes, and this error is
increasing by about one minute per year.

OSCAR-11 now operates in a default mode, controlled by the watch-dog timer.
The satellite transmits continuous ASCII telemetry for about 8 - 9 days on
145.826 MHz., followed by about 10 - 12 days of silence. This regular
sequence might be interrupted by ground control.

The mode-S beacon is ON continuously, even when the VHF beacon is
OFF, nominally transmitting an unmodulated carrier on 2401.5 MHz.
There is however a VERY low level of AFSK modulation, (now a constant
1200 Hz. audio tone), which has been detected on strong signals.
Telemetry indicates that the beacon has partially failed, and is
delivering half power.  This beacon is a useful test source for those
testing mode-S converters, as an alternative to OSCAR-40. However the
signals are very weak, and there is a lot of Doppler. Users should
also note that the polarisation of OSCAR-11 is LHC. Even if you can't
hear OSCAR-11, your equipment may still be OK for OSCAR-40. Any
reports of reception on 2401.5 MHz. would be most welcome.  Please
e-mail g3cwv@amsat.org.

The 435.025 MHz. beacon is normally OFF.  It can only be heard on the
very rare occassions when the satellite is being commanded by ground
control, ie. within range of Guildford, UK.  When the 435 beacon is
transmitting, the 145 beacon is normally OFF.  The data transmitted
is mainly binary.

Listeners to OSCAR-11 may be interested in visiting my web site.

The web site contains details about using a soundcard for data
capture, and also details about using hardware demodulators. There is
software for capturing data, and decoding ASCII telemetry and WOD.
There is an archive of raw data for analysis, which is continually
being expanded, as new data is captured.  Originally this was for
WOD, but it is now being expanded to include ASCII telemetry. At the
present time the telemetry covers 1996 to April 2003.  I will add
other years as time permits.  In parallel there is a news archive
which provides an overview of the state of the satellite, at the
times when the telemetry was captured.

If anyone out there can provide any data, particularly for the 1984
to 1993 years, this would be most appreciated.  Please e-mail me
with details.  However please DO NOT SEND ANY FILES, before futher
discussion.

Also included are some audio files, examples of each type of data
transmitted by OSCAR-11, each one plays for about ten seconds.  There
are also examples of mode-S reception.  All the audio files are
zipped, so that they can be played off-line.  These should help
listeners identify the various types of data, and give an indication
of the signal quality required for successful decoding.

The URL is -

      http://www.users.zetnet.co.uk/clivew/

If you place this bulletin on a terrestrial packet network, please
use the bulletin identifier $BID:U2RPT87.CWV, to prevent duplication.

73 Clive G3CWV   g3cwv@amsat.org

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