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External GPS Antennas for recreational grade GPS receivers

Here we will look at different types of external GPS antennas and their usage. We will not treat antennas for surveying, nor antennas for use on boats or planes.

Passive Antennas

Passive GPS antennas do not include a Low Noise Amplifier (LNA). When connected to a GPS receiver, it is the internal amplifier in the GPS receiver that amplifies the weak signal of the passive antenna. So when should one use a passive external antenna? In situations where you have a clear view of the open sky, but where your GPS receiver has a, partly, obstructed view of the sky. Best example is when driving with a GPS receiver in the car. Especially 4 x 4 vehicles, who often have rather vertical windshields, do not give a sufficient view of the sky for the GPS receiver. Modern cars often have a heat-reflective metal layer on the windshield, which attenuates or even totally blocks the signal from the GPS satellites. A passive GPS antenna on the roof will see more satellites, but there will be some signal loss in the cable. In most situations total reception will be better with than without a passive antenna, but an active antenna is anyhow preferable.

We only present two models of passive antennas. Northstar has the AN-145 passive antenna. Taewung has the TWG-202, that can be delivered with a SMA, SMB, OSX (same as MCX), TNC, BNC or GT5 connector.

Active Antennas

Active GPS antennas are passive antenna elements with a Low Noise Amplifier (LNA) incorporated in the housing. The LNA needs electrical power for its operation. The DC current as well as the HF GPS signal pass through the same cable, so only GPS receivers that provide a DC voltage on their antenna entrance, can accept these active GPS antennas. In order to avoid mutual influence of the external antenna and the internal antenna in the GPS receiver and to minimize the problem of multi-path signal degradation (the two antennas can be separated by several meters), the internal antenna is often switched off as soon as the GPS receiver notices that an external active antenna is connected.

How does the GPS receiver know whether you connected a passive or an active antenna to its antenna entrance? It detects a minimum current drain through the antenna connector. Often a value of 5mA is mentioned. So, if the external active GPS antenna drains less than 5mA, which is great for the batteries, the GPS receiver does not switch off its internal passive antenna. In that case and under certain conditions it will be advisable to obstruct the internal antenna in the GPS receiver with a sheet of Alu foil or similar.

As the GPS receiver and the external active GPS antenna use the same battery-set, the batteries in the receiver, the two should be matched. A 5V external antenna will not function as an active antenna when connected to a 3V GPS receiver. And a 3V antenna, connected to a 6V receiver, will drain a lot of current from the batteries and even risks to be damaged.

When to use an external active GPS antenna? In all cases where your GPS receiver has no clear view of the sky. Examples: in the car or when trees, high buildings or mountains obstruct part of the sky. We will categorize the active antennas according to their supply voltages.

Series 2.5V to 3.3V

The WI-SYS 3914 is an extreme low current active antenna: typical 2mA at 2.7V. The noise figure is extremely low at 0.8dB. Sarantel offers the GeoHelix-A. Operating voltage 2.0 – 3.5V at 11.5 – 15.0mA with a noise figure of 1.2 dB typical. This type of antenna has a greater field of vision above the horizon and has a very low Near-Field. This means that their performance is not affected when in close proximity to objects-including human tissue.

Series 2.5V to 5.5V

TRI-M’s popular Mighty Mouse II active GPS antenna has a 3-stage LNA and RF filter. The current consumption is at a constant value of 5mA over the entire voltage range. A 28dB gain and only 1.6dB noise figure complete the picture. Available with MCX and BNC connectors. San Jose Navigation, Inc. (Sanav) believe that their MK-76 Mini GPS Antenna is the most compact on the market. Current consumption 12mA. The MK-76 is compatible with almost every GPS receiver.

Their SM-76 is a low noise model with a 12mA current consumption. Available with every possible connector. Sanav’s SM-19 is a low voltage, low current and low noise active GPS antenna. Current 4.5mA and noise figure 1.3dB max. Available with MCX and BNC connectors. The Titan 3 GPS Antenna is a high gain, low current active GPS antenna. Current 5mA and a total gain of 28dB. Works with all Garmin and Magellan GPS receivers that accept external antennas.

Series 3.0V to 5.0V

The WI-SYS 3910 is a high gain, low noise active GPS antenna. A gain of 28dB at 3V and a noise figure of only 0.8dB. Supply voltage 3.0 – 5.5V. Current 7.5 – 11.5mA. Wide range of connector types available. TRI-M’s Micro Mouse has a 24dB gain at a max current of 12mA. Available with different connectors, straight and right-angle. Sanav has also the Mini GPS Antenna MK-4, which is "the most diminutive GPS antenna currently available on the market". Current 11mA and 26dB gain at a noise figure of 1.5dB max. All straight and right-angle connectors available. GPS4Less sells it as the BS-2 Mini GPS Antenna.

The Etek MA-35 delivers a 26dB gain with a 2.5dB Noise figure. Current consumption 11mA at 5V. Connector types available: BNC, TNC, FME, GT5, MCX (OSX), SMA, SMB or SMC in straight or right angle.

From Jiashan Jinchang Electron Co.Ltd (jinchanggps.com) comes the GAACZ-A with a 28dB LNA and a Noise Figure of 1.5dB. Supply voltage 3.0 - 5.0V at 11 - 15mA. Connector types: SMA, SMB, SMC,BNC, FME, TNC, MCX, MMCX or other.

Series 5,0V

Rojone’s MicroNav is a low cost active GPS antenna with a noise figure of 1.5dB typical. Current 14mA and amplifier gain 27dB typical. Available with SMA, SMB, MCX and BNC connectors. TRI-M’s Big Brother is a high gain, 30 dB typical, active GPS antenna for 4.5-5.5V at 28mA. The noise figure is 2dB max. Available with all straight and right-angle connectors. Sanav's HA-26 is a 4.5 - 5.5V, 28mA, 30dB omni-directional antenna, that receives excellently in all horizontal directions.

Series 3V and 5V versions available

Laipac’s P1 is a 3V/5V/16mA active antenna with a typical amplifier gain of 27dB and a typical noise figure of 1.5dB. Available with a variety of connectors. Centurion has the GPS Telematics Antenna in 3V and 5V version. Both 15mA max. 26dB gain and a noise figure of 2dB max. G-COM’s GPS Micro RX is "the smallest GPS Active Antenna on the market". Available in 3V and 5V versions with FME female connector. The Vic-1 by Aromat Antenna is a 26dB active antenna that comes in a 3V and a 5V version with SMA connector. The GPS AT-101 from Fortuna Electronic Corp. is an 27dB typical active antenna with a noise figure of 1.2dB. Both the 3V as the 5V version need a max current of 22mA and they come with a BNC, SMA, SMB or MCX connector. GlobalSat has the AT-25 in 3V and 5V versions. DC current is typical 25mA, the amplifier gain 27dB with a noise figure of 1.2dB. Available with a variety of connectors.

Series 2.5V to 12.0V

The RST-8776 is a 26dB gain active antenna with a 1.5dB noise figure that operates in the range of 2.5V – 12.0V. It is available with a BNC, TNC, SMA or SMB connector. StarsNav Tech's STR-1 and STR-3 GPS Antennas have a two-stage LNA and 28dB overall gain. Power consumption is 5-11mA. Available with all current connectors. The Garmin and Magellan compatible Gilsson antennas have a gain of 28dB. The operating voltage is 2.5 - 12V at a 5 - 11mA current drain. These antennas come with BNC, MCX, SMA, SMB female or SMB male connectors. You can also find these antennas at the GPSgeek site.

Re-Radiating Antennas

And if you think that you need an active GPS antenna and your GPS receiver does not have a connector for an external antenna? There is a rather simple solution to this problem. When an active GPS antenna, that reads the satellites, is linked to a passive antenna, the passive antenna will radiate an amplified signal of the satellites, received by the active antenna. This amplified signal can be picked up by your GPS receiver. This way your GPS receiver gets a stronger signal than without the two other antennas, who are not physically linked to your receiver.

As we saw above, an active GPS antenna needs electrical power to do its job, and as there is no link to the GPS receiver, we can not take it from there. So we need an extra power-supply for the active antenna. This could be a set of batteries or the 12V car battery.

As the passive antenna radiates at exactly the frequency for which the active GPS antenna is so sensitive, it is clear that the two antennas should be HF invisible for each other, as otherwise a closed-loop could occur. The result would be unpredictable and vary a lot with the position to and the visibility of each other. A closed-loop could easily lock up or even destroy the LNA in the active antenna and/or the electronics between the two antennas.

Let’s look at some ready-made solutions.

From San Jose Navigation, Inc. (Sanav) come the RA-45 and RA-46. Both use the SM-66 active GPS antenna to capture the satellites. The radiating antenna of the RA-45 is a small rod in the form of a pencil. The RA-46 is equipped with a much bulkier Helix type indoor re-radiating antenna. Both models obtain their power from a car battery by means of a cigarette-lighter plug. The Vortech re-radiating GPS antenna is very much the same as the RA-46. Also for in-car use. The Tri-M re-radiating antenna with the Big Brother active antenna is discontinued. Instead they now use the Mighty Mouse antenna for their WIDE-GPS re-radiating kit. Also very much the same as the RA-46. Also fed by the 12V car battery.

If you only have one cigarette-lighter plug in your car, all the above-mentioned models will occupy it and you can not feed your GPS receiver from the car battery. That is why the Haicom re-radiating antenna, which is basically the same as the RA-45, is a handier solution, as its cigarette-lighter plug allows a second such plug to be inserted in its back. This way you can feed both the re-radiating antenna as well as the GPS receiver from the car battery.

And for those occasions that you want to use a re-radiating antenna outside the car, there is the PC-Mobile solution. Besides the SM-76 active GPS antenna, it consists of a small box, containing 3 AA size batteries and the feed for the radiating antenna. And this antenna could not be simpler either, as it is not more than 1m of antenna cable, ending in a small loop, that needs to be fixed to the GPS receiver’s antenna (with a rubber band or adhesive tape).

Smart Antennas

Smart Antennas are more than active antennas. They are complete GPS receivers. These are the TYPE 1 receivers as described on our GPS-Types page and they are the "Small GPS receivers with a cable (GPS mice)" from our Car-GPS page. We will categorize the smart antennas according to the technology, used for the GPS receiver.

SiRFstar II low power

The Falcom NAVI-S consists of a high-performance GPS core including acquisition accelerator, DGPS processor, multi-path mitigation hardware and satellite tracking engine. It can be connected to all type of equipment that supports RS-232 or USB type. The S-1 comes with a magnetic base and the S-2 with an adhesive pad. The price of Euro 79.- invites to experiment. GlobalSat has the BR-304 GPS receiver with RS-232 Interface for PC and the BR-305 for PC, pocketPC and Palm. RoyalTek has the RGM-2000 Sapphire, which fits perfectly for laptop, notebook, pocketPC and Palm users. It provides USB and RS-232 interfaces with various connecting cables for different devices. The Haicom 204E comes with a PSII to PDA plug. For most pocketPCs and Palm PDAs there are cables available with 12V cigarette-lighter plug. The Rayming TN-200 comes with an USB connector and a driver to convert the USB port into a virtual COM port. A Mac driver is also available. The Rojone Pty. Genius 1 also comes with an USB connector and provides a Time Mark TTL output which is 1 pulse per second, aligned to a GPS second, +/- 1 microsecond. Standard NMEA or SiRF Protocol.

From Holux comes the GM-210 waterproof GPS receiver with magnetic base. The 210-99 is a 6-30VDC/0.75W version and the 210PS is a 5V/0.75W version. It connects to Laptop, pocketPC and Palm device and drivers are available for Windows, Mac OS and Linux. EGNOS ready. The GPS 9532 from Leadtek can be configured to work with a variety of handheld PC, notebook, pocketPC, Palm devices or specialized systems. The housing contains a 3V lithium battery for data backup. It supports standard NMEA-0183 and SiRF Binary protocols. Fortuna Electronic Corp. offers the U2 and the MEII, which have different housings, but are very much the same GPS receiver. They come in RS-232 and USB versions and the power supply can be either 3VDC or 5VDC. Both 160mA typical for Continuous mode. They support NMEA-0183 and SiRF Binary protocols. The Rikaline GPS 6010 X5 is a high sensitive (Xtrac) Mouse GPS receiver, that is WAAS and DGPS enabled. It has a rechargeable backup battery on board, that is automatically re-charged during normal operation. This way critical satellite data can be saved for 1000 hours. The standard model is RS-232, but an USB version is also available. A series of cable sets are available to let it communicate with PC, pocketPC and Palm devices. The StarsNav Cobra-X has a SiRFStarII XTrac chip-set with an internal back-up battery. It is DGPS and Waas enabled and can come with different connectors. But what it makes special is that it comes with its own in-line Power Supply (3 rechargeable AA batteries).

SiRFstar I

The Leadtek GPS 9531 is a 5V/0.9W receiver, which comes with an universal connector RJ11. Communicates in NMEA-0183 and SiRF binary and is ideal for use with PC, pocketPC, Palm devices and other Computing devices through different adapter cables. From Laipac come the G10-R with a 9-pin Serial connector and the G10-U with an USB connector. Power is derived from a standard PS/2 plug. Being based on the NMEA protocol the receiver is compatible with virtually all freeware, shareware and commercial GPS mapping programs. Changing receiver outputs requires simple text commands via a terminal program, such as PROCOMM PLUS, or common terminal program included with Windows. The GPS-SM133 from Steminc comes with a DB-9 serial connector and complies with the NMEA-0183 data message standard and SiRF’s binary data protocol. Power supply is 5.0V/0.9W. The receiver works directly with a host computer. This could be a PC, pocketPC or Palm PDA.

Trimble FirstGPS

The RoyalTek RFG-1000 Onyx has a very low power consumption of less than 20mA. It is available with a RS-232 serial connector (power coming from a PS/2 port) or an USB connector. Drivers available for PC and pocketPC. Adapter-cables are available for a variety of pocketPCs.

Other/unknown

The Haicom HI-202E with USB connector is for Notebook, PC use. Because of the standard NMEA-0183 V2.2 output protocol it communicates with almost all GPS software. The Haicom HI-203E is not only for Notebook or PC, but by means of the appropriate cable-set, with 12V cigarette-lighter plug, it can communicate with a variety of pocketPCs and Palm PDAs.

The Garmin GPS 35 PC has an attached 10 feet power/data cable with female DB-9 serial connection, ready to attach to your PC. It has an additional 8 feet power cable extension from the DB-9 connector terminating in a cigarette lighter plug for easy application of power supply voltage between 6 and 40VDC. It also features an asynchronous serial data interface via a single serial port with true RS-232 voltage level output. Typically draws 80mA at 12VDC and has an internal 3V Lithium battery for data back-up. This receiver offers the choice of 102 map datum’s.

Also from Garmin is the GPS 16 WAAS enabled Receiver. It comes in 3 versions. The 16LVS low voltage 3.3-6VDC, the 16HVS high voltage 6-40VDC and the 16A with a 5Hz update rate. This well-documented professional receiver does not have the usual prof price tag. The Pharos iGPS-180 has the dimensions of a matchbook, needs little power and is water-resistant. It comes with a standard female PS/2 connector. It has the versatility to connect to all PDA applications as well as laptops. A variety of cable assemblies with a 12V cigarette adapter is available for pocketPCs. A universal PDA (DB9 male) and an USB cable assembly are also available.

The Etek GM-168 is a high sensitive GPS receiver with a uNav chipset. It delivers a very fast TTFF. The primary power is 3.3 - 7.5V and a current consumption of 70mA at 3.3V. Via the RS-232 interface it delivers the NMEA-0183 v3.0 protocol with a baud rate of 4800 to 38400. NMEA messages: GGA, GLL, GSA, GSV, RMC and VTG.

Some often used connectors

FME and MCX connector

Left is the universal FME female connector
and right a right-angle adapter to MCX.

BNC and MCX connector

Left is the BNC connector and right the
FME-MCX combination.