GPS Antenna | When is an Active Antenna really Necessary?
Active antennas contain a low noise amplifier and possibly a filter and line driver.  It is very important to put the LNA as close to the antenna as possible to get some gain before the cable loss.  The trick with GPS is that the signal is extremely small.  The GPS signal is actually below the noise floor of the LNA, so adding more gain really does not help at all above mitigating the loss in the cable.  What does help is the coding gain in the receiver when it despreads the signal.  This does not depend on the receiver as the coding gain is dependent on the design of the code.