A GPS filter protects your receiver from unwanted interference signals, and enables excellent reception. Ultimately, a filter is a circuit that performs signal processing functions in order to remove the unwanted signal components and enhance those that are wanted.
GNSS receivers function by separating the desired signal from all other signals. They do so by matching their self-generated signal code with that of the satellite code; but there are several factors that can make this difficult and detract from the receiver’s ability to determine the intended signal. These factors include things like ionospheric and atmospheric delays, satellite and receiver clock errors and selective availability, among others. In order for a receiver to operate at peak performance, it must be able to receive the intended signal clearly despite these factors, usually with the help of a GPS filter. These filters are designed to accept the signals of desired frequencies and reject signals of unwanted frequencies.
One of the most common sources of signal degradation, detracting from a receiver’s ability to carry out its intended function, is electromagnetic interference (EMI). EMI can originate from an external source, or even from within the receiver itself, and can inhibit a GNSS receiver’s ability to receive a clear signal. The main function of a GPS filter is to protect receivers from such noise and interference by filtering and rejecting the unwanted interference, and passing signals through. By filtering the signal before it gets to the receiver, the effect of internally generated electrical noise is reduced.
Whenever GPS reliability is of the utmost importance, or there are known interference sources, a filter should always be installed in order to ensure that the intended frequencies are allowed through, and that all other interfering signals are blocked. For example, in some urban settings, GNSS antennas must sometimes be located near transmitting antennas, which can interfere with signals. In these cases, a GPS filter (or seomtimes more than one) should be installed near the receiver to reduce or eliminate the offending signals.