Today, the market is filled with different types of GPS receivers. The GPS system can be a portable or integrated one but most of them come with an internal in-built antenna. However there are antenna of different types and sizes. Most of the external antennas can be classified into three broad categories; active, passive and re-radiating antenna.
Types of External Antennas
Active Antenna : An active antenna is defined as an external antenna that includes a low noise amplifier. This low noise amplifier is necessary to make up for the loss of signal that may occur in antenna cables. Active antennas consume less power from the GPS unit for power the low noise amplifiers.
This power is incurred via the receiver’s external antenna’s socket. As they require power to run these types of antenna can drain out the device’s battery. In case you are using an active antenna, do ensure to carry extra packages of batteries with the navigational unit.
Passive Antenna : Passive Antennas are also known as substrates. They do not include a low noise amplifier. The absence of low noise amplifier eliminates the need for additional power. Thus there is no strain put on the battery of the satellite navigator. As these types of antenna do not require power, their cable length is limited to just one metre.
Re-radiating Antenna : The re-radiating antenna system consists of two antennas. The receiving antenna is placed outside the vehicle and the transmitting or re-radiating antenna is situated near the satellite navigator. The two are connected by a coaxial cable while the system is powered by either an AC adaptor or a 12 volt vehicle power supply. A re-radiating antenna is required only if the sat nav does not have a jack for connecting an external antenna.
A socket for connecting an external GPS antenna is most often provided on all navigational systems. Although, there is a slot provided, it is not mandate to use an external antenna, it depends on a variety of factors. The main reasons for using an additional GPS antenna is to have better signal reception. It will also be necessary if the GPS receiver cannot be situated near the window of your vehicle. It is useful when you go hiking in thick forested terrain or in canyons or mountainous areas. In case you are caught in a tunnel, then you may need an external antenna. In short, it is to be used wherever the vehicle cannot have a better view of the sky. This is done to improve the accuracy of the GPS signal and to be able to lock onto more number of satellites at any given moment of time.
Depending on the area of operation of the satellite navigator and the location of the unit inside the vehicle, you can decide on whether or not you need an external antenna for your unit.