Solar Argos/GPS PTT-100s
Since the introduction in 2001 of our first GPS enhanced solar backpack PTT, the 70g GPS PTT, we have progressed through six generations of these devices. Our latest weighs only 17g, allowing a bird weighing as little as 570g to be tracked with GPS accuracy. These units not only provide accurate locations (typically within ±18m) but have added a tool in the biologist’s arsenal to fight the negative effects of radio interference of Argos reception in several areas around the world. A single message from a GPS PTT equipped with our 2D software contains five accurate fixes from the five preceding days. In contrast, the Argos system alone cannot Doppler locate a PTT with a single message. Our 3D software reports altitude, position (latitude and longitude) and even heading and speed when the bird is flying.
How does a GPS PTT function?
Our GPS enhanced PTTs are much more complex than standard “Doppler positioned” PTTs. They consist of four major subsystems: a GPS receiver and antenna, a microcomputer/datalogger, an Argos uplink transmitter and a solar charged battery. The microcomputer continually runs through a complex program controlling all of these subsystems. Each unit is programmed with two independent duty cycles, defined by the customer. The first cycle defines the local times, “on the hour”, that the unit will attempt to obtain GPS positions. The second cycle independently commands the transmissions of the archived GPS data through the Argos system, typically every third day. Our unique ‘Satellite-in-View’ (SiV™) technology dictates the precise times of the transmissions to occur when there is likely to be a satellite above the horizon, thus conserving energy. At this point, the archived GPS positions are transmitted as “sensor data” in a series of Argos messages, each containing a checksum to verify its integrity. All of our solar PTTs, including our GPS PTTs, use the microprocessor to manage the solar charging of the battery, thus making data collection and night time transmissions of data through the Argos system possible (as opposed to less sophisticated PTTs where transmissions occur only during daytime when the solar cells are exposed to light). As a result, we offer very flexible GPS duty cycles where fixes may be taken at different, customer defined, times of the day or night, during different “seasons” at local times.