30 March 2010
OSCAR-11 achieved 26 years in orbit on 01 March! It was designed, built and launched within a period of six months, using commercially available 'off the shelf' components (COTS). Once again, congratulations to Professor Sir Martin Sweeting G3YJO, his team at the University of Surrey and groups of radio amateurs who also contributed to the project. Unfortunately, the satellite wasn't transmitting on its birthday, but was heard briefly, three days later.
This report covers the period from 23 February to 30 March 2010. During this time the satellite was heard during three passes on 04 March. Good signals were received, and decoded. There was also an unconfirmed report that it was heard on 25 March.
Due to eclipses, deterioration of the battery and other parts of the satellite, it's not possible to predict when the satellite will be heard in the coming months. It is likely that it may be heard occassionally, by stations tuning around the beacon frequency.
The on-board clock was 263 days slow, when last heard on 04 March. The increasing error suggests that the clock may be stopping, when the satellite is in eclipse. Sometimes, the date counter also fails to increment. However, the retention of the date and time does suggest that a small amount of power may be still available during eclipses.
The Beacon frequencies are -
VHF 145.826 MHz. AFSK FM ASCII Telemetry
UHF 435.025 MHz. OFF
S-band 2401.5 MHz. OFF
Please send reception reports to xxxxx@amsat.org (replace xxxxx by g3cwv) or post to amsat-bb. If you have a file, please do not send it but let me know that it is available.
You may also like to add your reception report to the live satellite status page, on the website set up by David KD5QGR and Bob WB4APR. The URL is http://oscar.dcarr.org/index.php
The satellite transmits on 145.826 MHz., set receiver to NBFM. OSCAR-11 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 the OSCAR-11 page of this website, which may be useful for identification and as a test signal for decoding.
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 eclipses started around 2005 the watchdog timer often switched the transmitter off before the ten day on period had finished, during parts of the eclipse cycle. When eclipses became a permanent feature of all orbits, after April 2008, the transmitter switched off within a single orbit, thus the satellite was effectively non operational.
The satellite unexpectedly started regular transmissions in November 2009. Although there was a small variation in the length of eclipses, this wasn't enough to explain why the satellite started regular transmissions. It is possible that a fault developed, which prevented the watchdog timer resetting when the power supply fails, and now the watchdog timer settings are no longer retained during eclipses. The transmitter switches off during eclipses, and the real time clock stops during most of the eclipse.
When analogue telemetry was last received, in 2005, 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 26 years in orbit the battery has undergone over 100,000 partial charge/discharge cycles, and observations indicate that it cannot power the satellite during eclipses.
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 during ten minute passes the clock increments correctly to within one second. 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 day s ON followed by 10.4 days OFF.
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 )