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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
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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.
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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 ICOM .
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