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OSCAR-11 Report




                OSCAR-11 REPORT    22 May 2003

Users of OSCAR-11 may be interested to know that I have recently uploaded
some more ASCII telemetry & news archive files to my web site. The archive
now covers 1996 to April 2003 (details of website below).

During the period 14 April to 21 May 2003 the 145.826 MHz. beacon has been
heard transmitting continuous ASCII telemetry from 20 April to 29 April,
and from 10 May to 20 May. During this period good signals have been
received. Telemetry transmissions are expected to resume around 31 May for
about 9 - 10 days.

The internal temperatures have continued to fall, by about 2.5 degree C.
They are now 2.8 C, 1.0 and 7.2 C for battery, telemetry electronics, and
command decoder respectively. The temperatures are expected to continue to
fall slowly as the solar eclipse times lengthen, reaching a minimum in the
Summer, and then increase in the Autumn. The solar eclipse times should be
shorter than last year,resulting in higher temperatures in 2003.

The battery voltage observed during daylight passes has decreased slightly.
Observations have varied between 13.1 and 13.8 volts, with an average
value of 13.4 volts.

The spin period has increased steadily from 348 to 940 seconds, and was 782
seconds, when last heard. There is a danger that the long spin period may
result in uneven heating of the satellite's surface, and possible loss of
directional stability. The attitude is now being controlled solely by the
passive gravity boom gradient, and there is no control over spin rate.

The spin period is calculated from the X & Y axis magnetometer telemetry
values. It is difficult to determine the spin period accurately, when it
approaches or exceeds the duration of a pass, and for values greater than
600 seconds it is necessary to measure the time difference between peaks of
the X & Y axes, and multiply the value by four.

Users of OSCAR-11 should note that the date in the telemetry is
advanced by three days.  The time is advanced by 18.5 minutes.

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. These times appear to be somewhat variable, and 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:U2RPT85.CWV, to prevent duplication.

73 Clive G3CWV   g3cwv@amsat.org

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