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