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OSCAR-11 Report




                OSCAR-11 REPORT    16 July 2001

During the period 09 June to 14 July there have been three noteworthy
events. Firstly I have received two reports of unusually strong
reception of the mode-S beacon.  These came from Colin VK5HI, and
Chris G4SDG. Both stations reported hearing the familiar AFSK
OSCAR-11 modulation, when the signal was sufficiently strong to
quiet the receiver in FM mode. Colin reported signals 10 - 11 dB
above the noise using a 77 cm dish, while Chris receive S9 signals
using a 1.5 metre dish.  Both stations used SSB converters.  The
modulation received by Chris was good enough to demodulate, and about
90% of a single status frame was correctly decoded. Occasional
familiar words from a status frame were also detected in Colin's
reception.

A possible explanation for these strong signals might be that the fault
which has caused low output power for many years, may be
intermittent, perhaps triggered by the lower battery voltages which
are currently occurring.  Ground control have confirmed that the
S-band beacon has the same modulation as the 145 MHz. beacon, but the
modulation level is very low.

Secondly, the rate at which the SEU counter increments has
approximately doubled, to about 390 counts per day.  Decoding the
SEU binary telemetry shows regular memory failure at locations 3EC0
and 37B1. Less frequent faults at 1873 and 18F3 have also been
recorded.  The failure of 3EC0 started around 12 May 2001.  Location 37B1
failed in August 1994. Unfortunately the presence of permanent memory
failures masks the occurrence of less frequent random memory failures,
which could be observed before the 1994 failure.

Thirdly, the Z-axis magnetorquer counter reached its limit of 1024 on
23 June.  This has stopped further active attitude control.
The satellite's attitude is now controlled solely by the passive
gravity boom gradient. Prior to June 23 the spin control had been
working well, with periods in range 338 to 343 seconds. There were
155 Z pulses, three spin+ and 73 spin- pulses. Since counter
saturation the spin period has drifted to 582 seconds. Ground
control operations to reset the counters are expected in the near
future.

Reliable signals have been received from the 145 MHz. beacon. The
battery voltage observed during daylight passes is unchanged.
The average value observed was 13.4 with a range of 13.0 to
13.5 volts.

The internal temperatures have continued to decrease by a further one
degree C. They are now -1.2C and -2.6C for battery and telemetry
electronics respectively.

The WOD survey of channels 1, 2, 3, 61 (X, Z, Y magnetometers and
status) dated 24 March, has been transmitted. This WOD may now been
downloaded from my web site (details below).


In addition to the reports by VK5HI and G4SDG, the mode-S beacon has
also been heard by Edgar DF2MZ, David G0MRF, Ken G8VR, Neil G4HLX and
David 9M2DT .  Edgar uses an 18 turn helix into a DB6NT converter and
PCR-1000 receiver. Signals are 3 dB above noise. David G0MRF reports
3 dB above noise with a 26 turn helix and Drake converter. Ken just
managed to hear weak signals while setting up a new converter. Neil
has now added a DB6NT pre-amp to his Drake converter, and 16 turn
RHCP helix. He reports signals 2-3 S points above the noise.  David
9M2DT reports signals 2 dB above the noise. Many thanks for those
reports.

Users of OSCAR-11 should note that the hardware generated time in the
ASCII telemetry is now 15.5 minutes ahead of UTC, and the date is
three days advanced.  Unfortunately these errors cannot be corrected.
There are also smaller errors in the software generated times,
advances of 3.5 in the status blocks, and 1.5 minutes in the binary
packets, which ground control should be able to correct. The dates in
the status blocks and binary packets are correct.

The operating schedule is unchanged.

        ASCII status (210 seconds)
        ASCII bulletin  (60 seconds)
        BINARY SEU (30 seconds)
        ASCII TLM (90 seconds)
        ASCII WOD (120 seconds)
        ASCII bulletin (60 seconds)
        BINARY ENG (30 seconds)

The ASCII bulletin (number 115) is currently a static message,
detailing modes and frequencies of all the amateur radio satellites.

There  are  additional  status  blocks  after  each bulletin is
transmitted, and between ASCII TLM and WOD.

The mode-S beacon is ON, nominally transmitting an unmodulated
carrier. There is however a VERY low level of AFSK modulation 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 when commissioning is
complete. Any reports of reception on 2401 MHz.  would be most
welcome.  Please e-mail g3cwv@amsat.org.

The 435.025 MHz. beacon is normally OFF.  However it can sometimes be
heard 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 of hardware required and some software for
capturing data, and decoding ASCII telemetry and WOD.  There is an
archive of raw data (mainly WOD) for analysis, which is continually
being expanded, as new data is captured.  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:U2RPT63.CWV, to prevent duplication.

73 Clive G3CWV   g3cwv@amsat.org

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