Most GPS Antennas assemblies contain both an Antenna element and a Low Noise amplifier (LNA). They are usually contained in a plastic Radome cover that is transparent to radio frequencies, but hopefully impervious to weather.
Shapes vary, but are dependent on the type of Antenna element inside. The three most common are:
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The 'double helix' type, which have long tubular covers,
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The 'crossed-dipole' type which have egg-shaped covers,
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The 'patch' type which use microstrip (idg-dipole technology) and may have low-profile flat-top housings.
For obvious aerodynamic reasons the latter are often used on aircraft, but also appear frequently in ground-based applications. Antennas with domed or pointed tops are generally more capable of rejecting the build-up of winter snow or autumn leaf-debris and are also less attractive to perching birds -- this may seem funny, but it is a real problem in some places.
All these types are fairly rugged as far as the Antenna element itself is concerned, but sometimes the LNA is more vulnerable both to electrical (static) damage and mechanical shock. Despite some optimistic manufacturers' specifications, it is advisable to avoid dropping any type of GPS Antenna during installation, and in particular to avoid fitting any unit known to have suffered this fate. The types with egg-shaped or domed tops are particularly easy to drop. To provide the best protection, both from static and mechanical problems, it is advisable to keep Antenna units in their packing until the mounting arrangements such as poles, masts, brackets etc. have been completed.
It is almost impossible to test a GPS Antenna without connecting it to a GPS receiver, so attempts to diagnose problems using a test-meter (or even a Spectrum Analyser) are at best pointless. In some cases, attempting to measure impedance at the Antenna connector can be fatal to the internal LNA, which is often a sensitive low-voltage Gallium-Arsenide semiconductor chip.
In particular it is essential that if RF cable-testing equipment is in use at a site, that the GPS Antenna is left disconnected from the cable until after all cable testing is complete. The power level required to destroy the LNA is very low. It is also important that the Receiver unit at the other end of the cable is disconnected during cable testing.
Most GPS Antennas assemblies contain both an Antenna element and a Low Noise amplifier (LNA). They are usually contained in a plastic Radome cover that is transparent to radio frequencies, but hopefully impervious to weather.
Shapes vary, but are dependent on the type of Antenna element inside. The three most common are:
-
The 'double helix' type, which have long tubular covers,
-
The 'crossed-dipole' type which have egg-shaped covers,
-
The 'patch' type which use microstrip (idg-dipole technology) and may have low-profile flat-top housings.
For obvious aerodynamic reasons the latter are often used on aircraft, but also appear frequently in ground-based applications. Antennas with domed or pointed tops are generally more capable of rejecting the build-up of winter snow or autumn leaf-debris and are also less attractive to perching birds -- this may seem funny, but it is a real problem in some places.
All these types are fairly rugged as far as the Antenna element itself is concerned, but sometimes the LNA is more vulnerable both to electrical (static) damage and mechanical shock. Despite some optimistic manufacturers' specifications, it is advisable to avoid dropping any type of GPS Antenna during installation, and in particular to avoid fitting any unit known to have suffered this fate. The types with egg-shaped or domed tops are particularly easy to drop. To provide the best protection, both from static and mechanical problems, it is advisable to keep Antenna units in their packing until the mounting arrangements such as poles, masts, brackets etc. have been completed.
It is almost impossible to test a GPS Antenna without connecting it to a GPS receiver, so attempts to diagnose problems using a test-meter (or even a Spectrum Analyser) are at best pointless. In some cases, attempting to measure impedance at the Antenna connector can be fatal to the internal LNA, which is often a sensitive low-voltage Gallium-Arsenide semiconductor chip.
In particular it is essential that if RF cable-testing equipment is in use at a site, that the GPS Antenna is left disconnected from the cable until after all cable testing is complete. The power level required to destroy the LNA is very low. It is also important that the Receiver unit at the other end of the cable is disconnected during cable testing.