, Number1Ion your FHdbKk u rcl Decoding OSCAR Telemetry PartII by James R. Miller G3RUH Pan I o f this ankle. (in the May '89 issue of 73) covered telemetry info o n OSCAR-9 (UoSAT - I) , OSCAR-II (UoSAT-2) . and OSCAR-13 (P3C). This final part co ve rs telemetry info on Fuji -OSCAR 12 (F-Q- 12). and some birds yet 10 be launched: Uo$AT-D and the Microsats. (Note that F..Q- 12 is NOT the same as Uo5AT-D.) Fuji OSCAR-12 Genera': JAS-I o r Fuji-OS CAR-12 was launched on August 12. 1986 from the southern tip of Japan. It carries two transponde rs: a traditional one for SSBI CWo and the world's first spaceborne packet radio 8RS. In orbit 1600 krn ( 1000 miles) high. it's inclined at 50 degrees to the equato r with a period of 120 min utes. It offers users an aggregate of two hours communication per day . When in SSBICW mode , it sends telemetry in Morse code on 435 .795 M Hz. When in the digital mode . telemetry and traffic is in the AX .25 packet format on 435 .910 MHz. Nowadays. FO·12 is somewhat troubled by insufficient power from me solar panels to support the digital mode full lime. The improved JAS-2 is in preparation and, based on the experience of its predecessor, it should be highly successful. Since the digital mod e supports a packet mailbox. users can aIM) transmit data in the 2 meier band 10 the satellite . The modulation format, however. is not the sarnc as for terresrnat packet. Ne vertheless. you do need a packet radio Term inal Node Controller (TNC). Data Transmit/ell: In the digital mode, FO-12 sends its telemetry in " unconnected" AX .25 packet frames , which appear on your terminal as seen in Figure I . You will see that the telemetry contains 40 numbers which you can decode into voltages. currents. temperalures. status points. CIC., using the published equations. For example . the first item is " Total Solar Array Current, rna." and decodes as I = 1.91 x (N-4). Selling N = 275. you find that th is current is 5 18 rnA . In addition to the telemetry data , you would 58 73Amateur Radio · June, 1989 • , • • • • • • • _.- PhotoA. FO-12 PSK Packet Radio Mod em . This uses regular CMOS/ ITL chips andno hard-to-get pans. This modem is used with the FO-12 flying BBS andAMSA T-NA 'sfonhcoming MicroSaIS . PSKmodems are also used for PSK pocker experiments terrestrialiv, through OSCAR 13 '.I' \v ia transponder. and ~\'en meteor scatter. - also be able to monitor the packet traffic . This looks no different from the familiar terrestrial scene, except it's faster! Telemetry Format: In contrast to conve n tional local packet radio. which uses two tones (A FSK) to signal binary "0" or " 1, " FO-12 uses phase shift key ing (PSK) modulalion. The carrier phase is changed by ISO degrees (in...'erred) when a change in binary level is signaled. The downlink carrier on 435.910 MHz passes through a balanced modulator driven hy the AX .25 dig ital data at 1200 bits!s to generate PSK . The uplink is different: 1200 bits/s data is excl usive-Op ed with its 1200 Hz clock (called " Manchester" coding), and th{s audio is transmitted FM on 145 .850, 145.870. 145.890. or 145.910 MHz . Telemetrv Demodulation : A PSK demodulator consists of a phase reference derived from the received aud io with a special phaselocked loop (PLL). and a phase detector to extract the phase changes and convert them to digital bits . In addition, the received signal is subject to 16 kHz total Doppler shift due to the spacecraft's movement, at a maximum rate of4O Hz per second. Tun ing the receiver by hand to follow th is is practically impossible. so an auto-tune ci rcui t is essential, especially ifyou want to turn antennas and operate a keyboard as well. The G3RUH FO-12 PSK Modem provides all the above functions plus an uplink modulato r. It has been available since 1986. with about 500 presently in use . This modem can also be used for experimental PSK work either terrestrially or th rough O SCAR-I3 ' s vo ic e transponder. A power advantage of some IOdB over normal packer signaling is typical. Decode rtstodem Specificotions: Downlink- Input 50 mV to 5V RMS audio from SSB/CW receiver . PSK demodulator. Output TTL digital, 1200 bps. Up link- lnput lTL digital. 1200 b ps : Ou t p ut . 1200 b p s Manchester encoding modulator to mike level. Connects-To AX .25 TNC"s " mode m d isconnect jack. " Suitable fo r T NC-2 a nd der ivat ives, such as T N C -200 , TNC-220 , Ti ny-2 , PK-80 , PK-87, PK·88 , etc. Digital AFC- Tracks changing Doppler shift via the up/down lines of all known <strong>ICOM</strong> . Trio/Kenwood. and Yaesu receivers. Controls-Auto-rune on /off'. PLL bandwidth , Leek/Tune/Power LEOs. Set-up-s-Three trim pots; PLL frequency, II.! supply voltage, and up/down tuning sensitivity set . Power/PC B-12V @ 40 rnA. Built-in AC PSU options . Double-sided plated through PCB, 160 x 100 mm . II ICs. 40 resistors, 25 capacitors. Availability.-.The PCB is available from AMSAT -UK (17 pounds airmail). You may also order it from AMSAT-VK and Project OSCAR. Rad ioKit sells the PCB plus full kit of parts . AMSAT·NA stocks no satellite products. though this could change in response to demand. Phone to check. All addresses and numbers are at the end of this article. Associated Equipment: You must use a 70 em SSB radio to receive FO-12 on 435.910 MHz, Tunin g rate should preferably be 20 Hz!step or benet. You can use 100 Hz steps. but at the expense of data errors when badly mistuned. You can take aud io direct from the e xternal speaker socket. Some receivers will
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