Aviation GPS antennas come in two varieties: active and passive. Depending on the length of the run of cable between your GPS and the antenna, one type of antenna may be warranted over the other. Active antennas are powered by the GPS receiver and require power from the GPS unit, whereas passive antennas are not powered by the GPS receiver.
Active antennas are used mostly for longer runs between the GPS receiver and its antennas. Runs longer than 3 feet may warrant the use of an active antenna. An active antenna is powered by the connection to the GPS receiver.
Passive antennas are used mostly for short distances between the aviation GPS receiver and its antenna. Antenna manufacturer Gilsson Technologies says that passive antennas are optimal for short runs between a few inches and three feet. Receivers that use passive antennas amplify the signal within the receiver itself, rather than in the antenna.
It may be dangerous to use a passive antenna on a long run if you do not do proper research. Make sure you contact your GPS manufacturer and antenna manufacturer before you make any sort of install for mission-critical GPS avionics. Always fly safe.
