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Beacon FAQ
1) Where is the beacon format documented ?
2) What do I need to receive QuakeSat's beacon ?
3) What's in the packet header ?
4) What is the year 1988 in the Beacon header...?
5) Why are the currents almost 0 ?
6) What are Jiffies ?
7) What is little endian mean ?
8) Have you found anything ?
9) What is I still have some questions ?
Answers:
1) Where is the beacon format documented ?
Please go to the QuakeSat homepage at
ssdl.stanford.edu/quakesat.
2) What do I need to receive QuakeSat's beacon ?
You need to be able to receive
QuakeSat on 436.675MHz and capture the
9k6 data stream. To do this you need also to be able to predict when
QuakeSat orbits above your location. Checkout www.amsat.org or
radio.linux.org.au for satellite
tracking and packet software. Andy,G0SFJ uses a Kenwood TMD700E, which
has a built in TNC (KISS ON), controlled by Packcom (freeware) packet
software. Because of Doppler shift, reception is best when the satellite
is at a very high elevation. G0SFJ used a 9 ele Yagi, capturing the
data to a file.
3) What's in the packet header ?
The 16 byte packet header contains the to QST from KD7OVB
call signs.
However depending on the software the value may need to be divided by
two. See the sample packet collect by Andy, G0SFJ
4) What is the year 1988 in the Beacon header...?
Like most computers. If the battery in your computer is dead, or not
there!, the computer will default to an initial starting time. The
Prometheus computer a (486) on QuakeSat does not have a battery, and
started is date/time from Jan 1, 1988, when it was released from the
Russian launcher. Since then QuakeSat has had continuous power. Setting
the correct data/time has been on the list of things to do, but way a
the bottom. We really have never gotten through this list! The time we
really care about is the Jiffie count. What that ( see question 6! ).
5) Why are the currents almost 0 ?
the values +-0.0000xxxx are close enough to zero to be called zero. All
current samples are handled by Multiplexer 1 which directly feeds one
of the Prometheus 16 A/D channel. Apparently the wiring did not
survive launch...
6) What are Jiffies ?
What all you friend promised to be back in!!.... A jiffie is 1/100th of
a second. The Prometheus computer runs the Linux operating system, and
the time from boot / reboot, is stored in an internal jiffie counter.
This jiffie count is used in time tagging of all data.
7) What is little endian mean ?
The format the data is stored in the file. Different computers are
describe and being big edian or little endian. All x86 machine are
little endian. An integer is 4 bytes long, let's say the bytes have the
values 1 2 3 4, this number would be store 4 3 2 1 in memory....
8) Have you found anything ?
Lots of equipment noise, which has been resolved, and that space
magnetically can be noisy! Please check out www.quakefinder.com for
announcement of payload data.
9) What if I still have some questions ?
Please contact Allen Lorenz (KD7OVB) at
allenlorenz@charter.net |
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