Shielding of GPS Satellite Signal

　　Based on the principle of the GPS system, the GPS receiver strongly depends on receiving satellite signals directly. In other words, it depends heavily on the range of the sky the receiver "sees" - the larger the sky range, the more satellite signals the receiver receives from different satellites, and the more accurate the positioning.

　　The GPS receiver receives 1575.42 MHz microwave signal from satellite. All natural weather phenomena will not block the GPS signal, which will certainly affect the positioning accuracy. Because of the satellite transmission power and distance, the signal is 100 times smaller than the background noise of the same frequency, and thousands of times smaller than the broadcast signal passing through your body. GPS handset uses complex digital signal technology to filter out the really useful signals. Therefore, the general radio interference does not pose a threat to the GPS receiver. The real threat is the occlusion of objects.

　　1. Penetration capability of GPS microwave signal

　　1) All metal entities completely block the GPS signal. Note that the car film with metal coating can also block GPS.

　　2) The water body (liquid) with a thickness of more than 1 cm will completely attenuate the GPS signal to be unavailable.

　　3) Glass and plastic have slight attenuation to the GPS signal, so you can put the GPS in your pocket, or under the windshield of your car, or insert the jacket at your waist.

　　4) However, thick non-metallic objects will completely block the signal, and a few centimeters of wood will completely block the GPS signal.

　　5) The wavelength of 1575.42MHz microwave signal is 19cm, so theoretically, it can pass through metal mesh with aperture (diameter) greater than 19cm, or ordinary metal quilting structure, such as power transmission tower.

　　2. Impact of tree crown on GPS signal

　　The attenuation of the tree crown to the GPS signal mainly comes from:

　　1) The water contained in the leaves, as well as the water on the leaves (dew or rain). It can be inferred that conifers have less influence on signals than broad-leaved trees.

　　2) The density of branches and trunks of trees.

　　The accuracy of GPS measured under the tree must be affected by the above factors, and the magnitude of the impact is affected by various factors. You need to use your own GPS receiver to test, so that you can know.

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