29 December 2011
This report covers the period from 01 September to 28 December 2011. The satellite has continued to operate in a very predictable way since the last report, and no changes have been observed. During this time the satellite has been heard reliably during its ten-day transmission periods. Excellent signals have been reported from stations located around the world, and good copy obtained from decoded telemetry frames.
The easiest way to check whether OSCAR-11 is operational is to look at the General Satellite Status website http://oscar.dcarr.org/index.php . You can also calculate the operating schedule from the last switch-off time, which was 28 December 2011 at 15:00 UTC (approx), using 10.35 days off followed by 10.35 days on.
Reception reports have been received from Gustavo LW2DTZ, Bob KI0G, Rolf HB9TSO and Francesco IT9JRU. Many thanks to all and those who posted to the status website.
The satellite is currently in eclipse during all evening passes over the UK, resulting in lower signal strengths at these times. Owing to the gradual precession of the orbit, the season for eclipses of the evening passes is longer this year compared with the winter of last year.
The on-board clock continues to gain, 28 seconds during the current reporting period, and 112 seconds since regular transmissions were resumed at the end of August 2010. There is however a large accumulated error of 308.54303 days slow. This was caused mainly by the clock stopping during eclipses, when there was also an unknown drain on the power supply. The units of the least significant digit correspond approximately to seconds (0.86 seconds actually).
The VHF beacon frequency is 145.826 MHz. AFSK FM ASCII Telemetry. The satellite is operating in the default mode, with a cycle time of 20.7 days. 10.35 days on followed by 10.35 days off.
At the present time, while OSCAR-11 is operating in a predictable way, I no longer need direct reports or files by e-mail. However, could all listeners continue to enter their reports on the general satellite status website. This is a very convenient and easy to use facility, which shows the current status of all the amateur satellites, and is of use to everyone. Reports around the expected times of switch-on and switch-off are of special interest, especially for times 12:00 - 18:00 and 22:00 - 09:00 UTC, when the satellite is out-of-range in the UK . The URL is http://oscar.dcarr.org/index.php
Transmissions are controlled by the watchdog timer, which has a 20.7 day cycle time, 10.35 days on, 10,35 days off. Solar eclipses occur during every orbit, when signals are weaker. This indicates that there is still some capacity remaining in the battery.
The operation during eclipses and stability of the on-board clock suggest that some part of the system may have recently failed 'open circuit' thus reducing the overall power drain of the system, and allowing more power to be available during eclipses. When analogue telemetry was last transmitted, an unexplained current drain was observed. This fault may have cleared.
The Beacon frequencies are -
VHF 145.826 MHz. AFSK FM ASCII Telemetry
UHF 435.025 MHz. OFF
S-band 2401.5 MHz. OFF
For the benefit of new listeners, here is a short history of OSCAR-11. It was launched in 1984, providing telemetry and other digital services for amateur radio and educational users. During its many years of operation it survived long periods of eclipses and continuous full sunlight.
In 2002 the satellite reverted to its default mode of operation, controlled by the watchdog timer. In 2005 all the analogue telemetry channels failed. Solar eclipses also started to cause the watchdog timer cycle to reset, which switched off the satellite for approximately 15 days.
In March 2008 solar eclipses became a permanent feature of every orbit, causing the satellite to switch off for about 15 days, probably after only one orbit of transmission. Thus the satellite was not expected to be heard again for any continuous period until 2019, when there will be some eclipse free periods. However, the satellite started regular transmissions unexpectedly in November 2009. It is likely that the fault which was causing an excessive drain on the power supplies, burnt itself out.
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.
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 20,7 day cycle. The ON/OFF times have tended to be very consistent. The average of many observations have shown this to be 20.7 days, ie. 10.35 day s ON followed by 10.35 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 )