What are the principles of GPS trackers for birds?

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????I have seen on TV that in order to study the living habits of birds, a gps tracker in the shape of a ring is placed on the legs of the bird. What is the basis for tracking?

????If it is wireless tracking, why is it so small?

????For such a small tracker, can the battery meet the requirements (at least 1 month)?

????For the above questions, I searched for the following answers:

????The bird's leg is a signal generator, and the human hand is a signal receiver, which can be tracked by positioning according to radio waves of a specific frequency.

????This is based on the difference in received signal strength in each direction to distinguish direction tracking.

????The current tracker has two modules, the transmitter and receiver modules. The transmitter module consists of two parts: one is gps (Global Positioning System) and the other is a signal transmitter. GPS can obtain the longitude and latitude of the signal transmitting point. The signal generator transmits this information, and then the receiver receives the information. Knowing the location of the launch point enables tracking.

????The user's gps locator emits a radio wave of a specific frequency, and a single channel in the gps tracker will reflect a specific radio wave, so that the target can be located like a radar, so the distance is limited; the advanced one is that there is one in the tracker class. The high-power radio wave transmitter, and the GPS tracker generates waves to the positioning instrument, so that the application range is wider; the most advanced is satellite positioning, that is, the GPS in the United States, the video captured by the satellite or other signals collected directly to the positioning device.

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