Campbell Scientific SAT ARGOS Argos Transmitter - Manual (Page 15)

SAT ARGOS
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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 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.
FIGURE 5-1. Complete Weather Station with PTT
13904 Antenna
Enclosure houses
the transmitter,
datalogger, and
power supply