Key Takeaways: Understanding GPS Antennas
- What it is: A GPS antenna captures radio signals from orbiting satellites, enabling a connected GPS receiver to determine precise location, speed, and time.
- Main Types: Antennas are primarily Active (amplified signal for better performance, needs power) or Passive (simpler, no amplification). External antennas often significantly boost performance over internal ones.
- Critical Factor: Proper installation with a clear, unobstructed view of the sky is essential for reliable signal reception.
- This Guide Covers: Dive deeper into basic terms, how GPS antennas work, testing procedures, various connector types, installation best practices, and signal splitting.
A GPS antenna is a device that receives radio signals from GPS satellites at varying frequencies. The antenna expands the signals and converts them into electronic signals so that they can be interpreted by a GPS receiver. The GPS receiver then uses these signals to give an accurate estimate of the receiver's location.Simply put, a GPS antenna helps you establish connectivity to the Global Positioning System (GPS). It is a system that was initially owned by the US Department of Defence. For years, GPS usage was limited for the military, but from 1983 onwards, civilians have been using it as well.If you've recently acquired a GPS antenna and are unsure of how to use it, this article should answer any questions you may have.
Some Basic Terms
Here are some of the basic terms you need to know before diving deep into using your GPS antenna.
GPS Antenna Splitter A GPS splitter is a device that allows you to connect an antenna to two receivers simultaneously.
GPS Antenna Input The GPS antenna input is used for satellite radio and GPS.
GPS Antenna Cable GPS antenna cables, primarily coaxial cables, are wires used to transmit GPS signals from a GPS antenna to a GPS receiver.Some cables can be used to connect a GPS device with an external GPS antenna or even an internal GPS antenna installed within a separate device. At one end of these cables, there is a radio frequency connector that connects with the antenna. GPS cables (coaxial cable) are usually short and often double shielded to keep signal loss to a minimum. The lower your signal loss or variance, the more accurate your GPS readings will be.
GPS Antenna Frequency The antenna frequency is the number of wave cycles per second. GPS signals are broadcast at sub-2 GHz frequencies by using the L-band of the radio frequency spectrum. Each GPS satellite uses two types of frequencies to transmit data, L1 (1575.42 Mhz) and L2 (1227.60 MHz).
A third frequency band, the L5 band has been introduced for civilian use. It has a frequency of 1176.45 MHz and a bandwidth of 12.5 MHz. It has been devised to be robust and provide access for high-performance applications such as aviation and 'safety-of-life' purposes.
GPS Antenna Mount A GPS Antenna mount is the mount used to attach a GPS antenna.Typically, you can install a GPS antenna in one of two ways; wall mounting or pole mounting. In both cases, keep in mind to face the mounted antennas towards the sky for best results.
Types of GPS Antenna
There are two major types of GPS antennas: patch and quadrifilar helix (or quad helix for short). Quad helix antennas offer better isolation, while the patch antennas offer more gain. Most GPS receivers also come with in-built antennas.
Are GPS Antennas Directional? No, GPS antennas are usually omnidirectional. This means that they can receive and transmit signals from and to different directions equally.
GPS Antenna vs. Receiver A GPS receiver is a device that locates multiple satellites, calculates their distances from one another, and then calculates its own distance from those satellites. This process of triangulation is what makes GPS receivers so accurate. The GPS antenna is responsible for converting and amplifying signals generated by the receiver, as well as interpreting signals from the satellite network.Most GPS receivers include a small omnidirectional antenna.
Active GPS Antenna vs. Passive GPS antennas can be either active or passive. An active antenna has an amplification stage, giving it greater accuracy and dependability over a wider reception range. Active GPS antennas are more complex than passive antennas and are more challenging to install.In contrast, passive GPS antennas have no amplification stage. Their accuracy is still adequate for most consumer applications, however.
Workings of a GPS Antenna
How Does a GPS Antenna work? Our earth is surrounded by numerous satellites that transmit radio signals down to you.
- The GPS antenna sends a signal to the satellites which the satellites then return.
- The signals are then processed by the receiver, which will calculate the time of arrival (TOA; at what time the initial signal returned from the satellite network to the receiver) and time of flight (TOF; how long it took for the signal to return).
- Using this data as collected from multiple satellites, the receiver than calculates its distance from each of the satellites it has pinged, triangulating its own current location.
Multiple cycles of this process occur simultaneously, and so the receiver can also extrapolate its own speed and direction of travel.Sometimes signals moving between the receiver and satellite network are delayed by interference in the upper atmosphere. In these cases, the receiver compensates for the delay when making its calculations.
How Does a Directional Antenna Work?
A directional antenna receives signals efficiently from just one direction. Directional antennas are more energy efficient, as they're not sending and receiving information from every direction, instead confining themselves to a single point. In this direction, they may pick up a weaker or more distant signal than an omnidirectional antenna using the same amount of power.
How to Use a GPS Antenna?
Generally, the internal GPS antennas work fine on most navigation devices. However, you may want to supplement your receiver with an additional antenna if it's older or under-powered.External antennas are often used when the path between the sky and your GPS device is unclear or restricted. In addition, external antennas can help increase the speed and accuracy of older GPS receivers.
Can a GPS Antenna Go Bad?
A GPS antenna could go bad if one or more of its components fails. If your GPS antenna stops working, it will need to be replaced. If the internal antenna on a GPS receiver stops working, you can replace it with an external antenna rather than having to replace the entire receiver.One common point of failure in a GPS antenna is the balun. The balun's job is to convert balanced signals into unbalanced signals. They're usually very durable, but are vulnerable to extreme temperatures. In some cases, a balun can rust. The wires within an antenna are also vulnerable to damage, and even external damage to the antenna's housing can cause it to become less effective over time.
Testing a GPS Antenna
How to Test a GPS Antenna?
You can test the performance of a GPS antenna with a spectrum analyzer. A spectrum analyzer is a device that evaluates the signals reflected from your antenna. Keep in mind that to test the performance of a GPS antenna you must connect it to a receiver.Apart from that, you must also watch out for two things:
- Signal degradation. Whenever a GPS receiver pulls signals from a satellite through an antenna, it suffers signal degradation. The reasons may vary, from obstruction caused by trees or high buildings to any sort of jamming, absorption, or delay in the atmosphere. A little bit of signal degradation is normal, but too much can interfere with ordinary function of your GPS system.
- Low noise amplifier. GPS antennas have two essential parts: an antenna assembly, and a low-noise amplifier. The latter is a semiconductor chip and susceptible to overload. That's because it is made of gallium arsenide, which is highly sensitive to voltage. So, while testing your GPS antenna, be sure to operate at low to moderate voltages to avoid damaging your amplifier.
How to Check Your GPS Antenna with a Multimeter?
A multimeter is an instrument that measures the electric current, voltage, and resistance of electronic devices over a variety of ranges. If you want to check your GPS antenna's resistance, you need to set the unit measurement of your multimeter to ohms, denoted by the ""Ω"" symbol. Then, follow these steps to get the most accurate results when testing your GPS antenna's resistance.
- Detach your antenna cable from the receiver.
- Next, pick one cord of the multimeter and touch its end to the antenna's metal part. Now, pick the second cord of the multimeter and touch its end to the antenna cable's end.
- Ensure that the reading on the multimeter is zero. If it is not, you may be using a damaged cable or antenna. This could prevent GPS signals from reaching the receiver properly.
- Now, touch one end of the multimeter cord to the metal core of the antenna cable connector and the other to a grounded object.
- Again, the reading should be zero, or else your antenna may be faulty.
Installing a Global Positioning System Antenna
Where Is the Best Place to Mount a GPS Antenna?
The ideal place to mount a GPS antenna is out in the open, allowing radio signals from orbiting satellites to reach the antenna uninterrupted. This way, your antenna will be directly facing the sky with no obstructions whatsoever.If you're mounting your antenna to a car, place the antenna in the middle of the car's roof. It's best to use an antenna mount to keep the antenna fixed to its position. Also, if you have any roof bars or radio antennas nearby, you must mount the antenna at least 5 cm away from them to keep the interference as low as possible.For any GPs antenna installation, refrain from placing the antenna close to the ground, walls, or the edge of a roof. This is because reflections from such objects may interfere with the signal significantly.
GPS Antenna to USB
If you're looking for a GPS antenna with a USB connection, you may not find it that easily. Such types of connections don't come with standalone GPS antennas, so the closest you'll get is a receiver with an internal antenna and a USB connection. This one by GlobalSat, sold by Amazon, is a good example.
GPS Antenna With SMA Connector
GPS antennas do not normally come with an SMA connector. However, you may get an F-type connector with them easily, which is a bit bigger than SMA.
GPS Antenna with NMEA 0183 Output
NMEA 0183 is designed to ensure a one-way data transmission from a "talker" device to one or more "listeners." There are many GPS antennas compatible with an NMEA 0183 output, including the Protempis (formerly Trimble) Acutime 360 Smart Antenna.
GPS Antenna With U.FL Connectors
U.FL and similar connectors, such as I-PEX, UMCC, or IPX, all support small coaxial cables of the kind used by most wireless devices. Most manufacturers and consumers prefer these connectors due to their compact size and low cost.Because these coaxial cables are smaller in size, they are much easier to manage.Unfortunately, if you are looking to get a U.FL connector along with your GPS antenna, you'll usually need to by your U.FL adapter separately.
GPS Antenna With a Blue FAKRA Connector
FAKRA connectors are high-quality SMB-based interfaces used in automotive applications. These connectors can even operate at up to 6 GHz.If you want to connect your GPS antenna with a blue FAKRA connector, you can do so with any of Trimble's Mini Mag Mount Antennas.
GPS Antenna With BNC Connector
BNC, or Bayonet Neill-Concelman, connectors come for almost all types of coaxial cables. These connectors are usually used at lower frequencies, typically below 4 GHz. They are available in both 50-ohm and 75-ohm versions.If you are looking for an upgraded version of BNC, you can go for TNC (also known as Threaded Neil-Concelman). This connector ensures its security with the use of threads that reduce leakage. As a result, the connectors get the opportunity to operate at higher frequencies, even up to 12 GHz.Another plus of using TNC is that it's waterproof, so you can use it for outdoor antennas and cell towers without any worry. You can also get these connectors in a reverse polarity variant.However, if your antenna only operates at frequencies lower than 4 GHz, you should go for a BNC connection rather than a TNC.
GPS Antenna and Receiver
A GPS receiver is an L-band radio processor that determines the location of the user, their speed, and the precise time (PVT) by processing the signals sent by a GPS antenna to orbiting satellites, which then return the signal to the antenna.
GPS Antenna and Repeater
GPS repeaters are devices that extend the range of GPS signals. They work by duplicating, or repeating, the signal from a GPS antenna. They're typically placed outdoors and used when a broad area of very precise coverage is necessary.
GPS Antenna and Cable
GPS cables are coaxial cables specifically designed to transfer GPS signals from an antenna to the receiver.
Splitting the GPS Antenna
Can You Split a GPS Antenna Signal?
Yes, you can split a GPS Antenna signal. With a good splitter, you can split the GPS signals into two or more receivers.
How Does a GPS Splitter Work?
A GPS splitter works by allowing one GPS antenna to be shared among two or more GPS receivers. For instance, a one-input, two-output splitter will split one GPS antenna between two receivers.
Can You Split a GPS Antenna Signal Among More than Two Receivers?
Yes, an antenna signal can be split between four or even eight receivers. An example of this type of GPS splitting is seen in a one-input, four-output splitter. The splitter splits the input among four receiving GPS units. These splitters work efficiently with C-RAN or DAS (distributed antenna systems). Meanwhile, one-input, eight-output splitters split a single input among eight output RF devices.
Can You Splice GPS Antenna Wire?
Yes, you can, depending upon the type of transmission line you are using.Some GPS receivers use a coaxial transmission line to connect to their antennas. You can splice this type of transmission line in case of any damage.However, remember to repair the wire in a way that won't change its impedance. You can use a multimeter to confirm the impedance of a repaired wire.In the case of newer receivers, most of the components of the receivers are squeezed into an antenna. These GPS receivers don't work in the same way as a standard transmission line. Instead, they have a multi-conductor cable. The cable supplies voltage to the receiver that generates an NMEA-0183 serial data output signal. Some may also have a conductor to assist in sending data to the receiver. With such types of cables, you don't have to sweat about maintaining the characteristic impedance. Thus, you can surely splice this antenna wire.
How Far Should the Cable from the Receiving Antenna be from the GPS Source Splitter?
When determining the distance between the source splitter and the receiving antenna, you need to consider the amount of signal loss. Splitter loss will account for a fraction of this signal loss. Splitter loss is due to the split ratio, input connectors, output connectors, and material and build quality of the splitter. If you're using high-gain antennas (35dB), receivers tend to operate well in the 13dB +/- 2dB range of total attenuation between the receiver input and the antenna. Receivers function well in the 6dB +/- 2dB attenuation range when paired with low-gain antennas (26dB). You can use a multimeter to test the signal at each of your receivers. After wiring up your antenna, splitter, and all of your receivers, remove one receiver from the chain and connect the multimeter in its place. This will tell you the strength of the signal being received by that receiver. Do the same in turn for each of your receivers, and make sure that the signal being received is in the acceptable range for each, respectively. To learn more about the line of Protempis (formerly Trimble) GPS Antennas. Or, check out the complete Protempis GPS Antenna Review.
Frequently Asked Questions (FAQs)
1. Do I really need an *external* GPS antenna?
Not always. Many modern GPS receivers have capable internal antennas sufficient for general use, especially with a clear view of the sky (like on a car dashboard). However, you typically need an external antenna if:
- Your GPS receiver is older or has a weak internal antenna.
- The receiver is placed where its view of the sky is heavily obstructed (e.g., deep inside a building, in a metal enclosure, below deck on a boat).
- You require higher precision or faster signal acquisition than the internal antenna provides.
- You are using a stationary device that requires a fixed, optimal antenna position (e.g., timing applications).
2. Can I use *any* GPS antenna with *any* GPS receiver?
No, not necessarily. You need to ensure compatibility in several areas:
- Connector Type: The antenna cable's connector (e.g., SMA, FAKRA, TNC) must physically match the port on your GPS receiver, or you'll need an adapter.
- Active vs. Passive: If your receiver is designed for a passive antenna, an active one might not work (or vice-versa). Active antennas require power (voltage) supplied by the receiver through the coax cable; ensure your receiver provides the correct voltage if using an active antenna.
- Impedance: Most GPS systems use 50 Ohm impedance. Ensure both the antenna and cable match this.
3. How long can the cable between my GPS antenna and receiver be?
Cable length introduces signal loss (attenuation). The maximum practical length depends on:
- Cable Quality: Higher quality, low-loss coaxial cable (like LMR-400 or better) allows for longer runs than standard RG-58 or RG-174.
- Antenna Type: Active antennas amplify the signal at the antenna itself, compensating for cable loss, thus allowing much longer cable runs than passive antennas.
- Receiver Sensitivity: A more sensitive receiver can tolerate more signal loss.
For passive antennas, runs are often kept under 10-15 feet with standard cable. For active antennas, runs can often extend significantly further (e.g., 50-100 feet or more with appropriate low-loss cable), but always check manufacturer specifications and consider overall signal loss.
4. How does weather (rain, snow, clouds) affect GPS antenna performance?
GPS signals (L-band frequencies) are generally robust and penetrate clouds, rain, and snow fairly well. Heavy rain or wet snow accumulating directly *on* the antenna surface can sometimes attenuate the signal slightly or shift its tuning, potentially causing minor degradation or slower acquisition. Dense storm clouds might add a small amount of atmospheric delay. However, for most standard applications, typical weather conditions don't prevent GPS operation, unlike heavy obstructions like buildings or dense foliage.
5. How do active GPS antennas get their power?
Active GPS antennas receive power through the same coaxial cable that carries the GPS signal back to the receiver. The GPS receiver outputs a small DC voltage (typically 3.3V or 5V) onto the center conductor of the antenna port. This voltage travels up the cable to power the low-noise amplifier (LNA) located inside the active antenna housing. It's crucial that the receiver provides the voltage required by the specific active antenna being used.
6. Which is better for my situation: an active or passive antenna?
It depends on your needs and setup:
- Choose an Active Antenna if: You need the best possible signal reception, have a long cable run between the antenna and receiver, or are in an area with potential interference. Ensure your receiver provides the necessary power.
- Choose a Passive Antenna if: You have a short cable run, a strong signal environment (clear sky view), your receiver is designed only for passive antennas, or you want the simplest/lowest cost option.
7. My GPS isn't getting a signal, what's the first thing to check?
Start with the basics:
- Sky View: Ensure the antenna has the clearest possible view of the sky. Move away from buildings, trees, overhangs, or anything blocking the signal. Even moving a few feet can help.
- Connections: Check that the antenna cable is securely connected to both the antenna (if detachable) and the GPS receiver. Ensure the connection isn't loose or corroded.
- Power (if applicable): If using an active antenna, confirm your GPS receiver is powered on and configured to supply voltage to the antenna port.
- Wait: Sometimes, especially on first use or after moving a long distance, the receiver needs several minutes (sometimes longer) to download satellite data (almanac/ephemeris) and calculate its position. Give it some time.
8. Do I need to worry about specific GPS frequencies (L1, L2, L5)?
For most consumer and standard commercial GPS applications (like vehicle navigation or basic asset tracking), an antenna supporting the primary civilian frequency, L1, is usually sufficient. Multi-band antennas (supporting L1/L2, L1/L5, or L1/L2/L5) are typically needed for high-precision applications like surveying, precision agriculture, or advanced timing, as using multiple frequencies allows the receiver to correct for atmospheric signal delays and improve accuracy significantly. Unless your specific application demands high precision, a standard L1 antenna is likely all you need.