2 environmental enclosure, Satellite orbit patterns, Antenna placement – Campbell Scientific ST-20 Argos Satellite Transmitter User Manual
Page 11
ST-20 Argos Satellite Transmitter
directional and unity gain. The antenna should be mounted vertically. An
antenna with gain will perform significantly worse then an antenna with unity
gain.
3.2 Environmental Enclosure
The ST-20 is designed to work in a dry, non-condensing environment. A
proper enclosure should be used to keep water, dust and other environmental
contaminates away from the ST-20. Always use desiccant inside the enclosure
to keep trapped moisture from condensing on the electronics.
4. Satellite Orbit Patterns
At least two NOAA Polar Orbiting Environmental Satellites (POES) carry the
Argos transceivers and are operational at any given time. The orbits carry the
satellites over the North and South poles of the Earth in a sun synchronous
pattern. Orbit period is close to 102 minutes. The satellite foot print is about
5000 km in diameter. At latitudes greater than 75 degrees, each satellite
provides coverage each pass. Each satellite passes over the poles 14 times a
day providing 28 satellite passes per day. Coverage decreases with latitude.
At the equator the PTT will “see” a satellite six or seven times a day. The
duration of the POES satellite visibility depends on the angle from the PTT to
the satellite. If the satellite passes directly overhead, the satellite will be visible
for about 15 minutes. If the satellite passes close to the horizon, as viewed
from the PTT, the satellite will only be visible for a short time. On average,
each satellite pass is visible for about ten minutes. If using a 200 second
repetition rate, a satellite pass could result in three received messages from the
PTT.
Satellite coverage must be considered when planning data collection and
transmission. Given the variability of satellite coverage, hourly data cannot be
expected unless the PTT is located above 75 degrees latitude. The number of
successful data transmissions per satellite pass will increase with a decrease in
the repetition rate.
More detailed information regarding Service Argos and satellite coverage is
available from Service Argos. On the Web, see http://www.argosinc.com/.
The Service Argos North American office can be contacted by email at
[email protected] or phone (301) 925-4411.
5. Antenna Placement
The position of polar orbiting satellites relative to the PTT will change during
the satellite pass and with each satellite pass. The antenna must broadcast
evenly to all areas of the sky. The antenna is omnidirectional. Mount the
antenna vertically. Choose a location with a clear view of the sky in all
directions. Any obstruction between the PTT antenna and the sky can block
data transmission between the satellite and the PTT.
7