21 APRIL 2008
RECEPTION REPORTS REQUESTED!
In the years ahead, it is possible that you may hear OSCAR-11, by accident, when tuning round the frequency. If you are able to record the satellite on audio tape or as a WAV file (not MP3), please do so, as it is unlikely that it will be heard on the next pass!
If you need to hear what the 145.826 Mhz. FM beacon should sound like, click here to hear a 10 second audio clip of the ASCII telemetry.
Please send reception reports to xxxxx@amsat.org (replace xxxxx by g3cwv) or post to amsat-bb. If you have a file, please let me know what you have, before sending it!
This is the 144th monthly report for OSCAR-11. Unless there is an unexpected change of status (such as occured with OSCAR-7), I'm expecting this to be my last report.
This report covers the period from 17 March to 21 April 2008. During this period the satellite has not been heard and no reports of reception have been received.
Transmissions were expected to resume on 24 March, after the beacon switched-off on 14 March. However, permanent eclipses started a few days beforehand, which probably caused the transmission period to be terminated prematurely. It is now unlikely that the satellite will support any sustained period of operation, and will only transmit for a short time, possibly less than a single orbit, every 21 days.
I am indebted to all those who sent reception reports during the last 12 years. Initially there was much interest in hearing the mode-S beacon, which was very weak. Recently, interest has changed to hearing when the two metre beacon switched on/off. Special thanks must go to Jeff KB2M who recorded telemetry during my holidays, and Peter ZL3TC, who has monitored the beacon daily, during recent months. Many thanks to everyone.
The Beacon frequencies are -
VHF 145.826 MHz. AFSK FM ASCII Telemetry
UHF 435.025 MHz. OFF
S-band 2401.5 MHz. OFF
The satellite is now subject to eclipses during every orbit. Long term predictions indicate that eclipses will occur until 2019, when there will be some eclipse free periods until 2023. However these very long term predictions should be regarded with caution, as large tracking errors can accumulate over long periods of time.
When telemetry was last received it showed that one of the solar arrays had failed, and there was a large unexplained current drain on the main 14 volt bus. After 24 years in orbit the battery has undergone over 100,000 partial charge/discharge cycles, and observations suggest that it cannot power the satellite during eclipses lasting more than about ten minutes, or sometimes even during periods of poor solar attitude.
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, although over short periods timekeeping is accurate to a few seconds per month. When last heard the clock was 83.0958 days slow. 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 show this to be 20.7 days, ie. 10.3 days ON followed by 10.4 days OFF. However, poor solar attitude may result may result in a low 14 volt line supply, which may cause the beacon to switch OFF prematurely, and reset the watchdog timer cycle. When this occurs, the beacon is OFF for 20.7 days.
OSCAR-11 was the second satellite from the University of Surrey, www.ee.surrey.ac.uk/SSC. It was designed, built and launched, within a time scale of six months, by a team headed by Martin Sweeting G3YJO. Amateur radio groups working at various locations in the world, also contributed to the project. It used commercially available 'off the shelf' components (COTS). Following the success of these satellites, in 1985 Surrey Satellite Technology Ltd. www.sstl.co.uk was formed, as a commercial venture. This grew into a major company which has produced over 27 small satellite projects for a global market.
The University of Surrey has recently agreed to sell it's major shareholding to EADS-Astrium. This agreement is now awaiting regulatory approval. The joint company will have the experience of manufacturing large and small satellites, for geo-synchronous and low earth orbits.
In regognition of his work, Martin G3YJO, was appointed Professor at the University of Surrey. He received an OBE in the 1995 Queens birthday honours list, and in 2002 a knighthood in the New Year's honours list.
Here is a sample frame of telemetry from the 05:46 pass on Thursday 28th. April 2005, showing that all channels have failed. Telemetry since then is similar.
UOSAT-2 0505024014454 000000010001020002030003040004050005060006070007080008090009 100001110000120003130002140005150004160007170006180009190008 20000221000322000023000124000625000726000427000528000A29000B 30000331000232000133000034000735000636000537000438000B39000A 40000441000542000643000744000045000146000247000348000C49000D 50000551000452000753000654000155000056000357000258000D59000C 60800E615FC1620141633341644402651E0C6630A967000168000E69000F
During the last few years I have received many enquiries regarding soundcard software for decoding OSCAR-11 signals, and from time to time there has been some discussion on AMSAT-BB about the need for this software.
A suitable Windows program for displaying and capturing OSCAR-11 data is now available. This is MIXW2, a general purpose Amateur Radio data communication program written by Nick Fedoseev UT2UZ.
You can download the program from Nick's website - www.mixw.net or if this is not available, a google search for MIXW will yield alternative sites. You need version, 2.07 or later.
The OSCAR-11 feature is un-documented at present in MIXW. I have therefore prepared a package of instructions and sample files, to help users. This is on the OSCAR-11 page of this website. Also included is a filter program which enables the data captured by MIXW to be used with the ASCII telemetry & WOD programs on the website.
I have found that MIXW2 works very well on OSCAR-11, and gives excellent results, comparable to a hardware decoder.
OSCAR-11 can be heard on 145.825 Mhz. Modulation is 1200 baud AFSK, with tones of 1200/2400 Hz. There have been many designs for suitable decoders, including the high performance correlation demodulator (used by ground control), designed by James Miller G3RUH. However the simplest way is to use an old telephone modem, using Bell 202, or V23 tones. It is essential to invert the modem's output signal, before feeding it into the computer.
A recent development is the use of a soundcard, as mentioned above.
It is also possible to use a BAYCOM type modem, which does not require any output inversion. Just connect its output to RXD instead of CTS.
Another way is to use a HAMCOM interface instead of a modem. A small program called EM1200M2.COM (which is part of EMBAYCOM) emulates a MODEM on port 2. Port 1 is used for the terminal display program. Unfortunately this method uses two COM ports, and can be a little tricky to wire up.
For ASCII, the serial port should be set to 1200,e,7,1. If the port is set up to eight bits, then some filtering of the data will be required before it can be displayed.
Further information, on the hardware can be found in the package uo11hw.zip on this web site. It is located between the data files and program files. Further details of software is contained in file CTERM.ZIP, which can also be downloaded from this web site.
Listeners living in the UK may have an old BBC computer, which may be used for decoding OSCAR-11 without the need for any external interfaces or hardware. The AMSAT-UK BBC library contains several suitable programs. Details from me, e-mail xxx@amsat.org (please replace the xx's by G3CWV ). These programs are NOT available from the AMSAT-UK office!
There is a simple OSCAR-11 telemetry decoding program U2TM, on this web site. It is written in BBC BASIC, but there is a compiled version which will run under Windows 95 onwards. The package also includes a small interpreter, which enables the program to be run on any PC with DOS. Being written in BASIC the program can easily be changed to suit individual needs, and is recommended to those wishing to experiment. Status decoding is included, and data from several channels may be combined. Examples of this feature are the calculation of total magnetic field, angle, and BCR efficiency. Please note that a capture program such a CTERM will also be required, which may also be downloaded from this site.
73 Clive G3CWV
xxx@amsat.org (please replace the xx's by G3CWV when e-mailing )