18x LVC GPS Navigator Unit

I purchased the GPS 18x LVC for NTP timekeeping purposes due to its highly-accurate 1-pulse-per-second output. This output is not available on the other GPS 18x models. For those interested only in navigation and not precision timekeeping, the GPS 18x USB model is probably the best option. As the LVC model is a "barewire" model meant for OEM integration, it requires a little bit of soldering to get setup the way one wants. I opted to connect the GPS to a small circuit board that supplies power to the GPS, has a fuse, and has indicator LEDs to show the state of the GPS: one LED shows that power is applied, with another LED shows when the PPS signal is transmitted. The circuit board has a DB-9 serial connection to the computer. Other people I know have connected the PPS and data wires directly to a DB-9 serial port and the power/ground wires to a male USB-A plug without any LEDs. Either way works fine -- the GPS draws about 60mA by itself (mine draws 75mA with the LEDs) and so can be powered easily off of a USB port (which can supply 100mA without the device needing to ask for more power). It's difficult to rate the GPS unit itself as it's so simple and there's not a whole lot of features: supply it with power, let it see the sky, and it starts outputting data. It managed to find an initial lock and output PPS signals within about 3 minutes of when I turned it on for the first time. Since then, it's able to reestablish a lock within about 5 seconds after being powered down and turned back on again. For testing purposes, I have it inside my apartment on top of a box placed next to my northeast-facing window and it is able to see between 5 and 9 satellites depending on the time of day. While no GPS receiver is meant to operate indoors due to the very weak strength of the GPS signals, the 18x is quite sensitive and gets quite reasonable signal indoors. The receiver is WAAS/EGNOS-enabled for improved precision (~3m vs. 10-15m). As the window in my computer room is on the northeast side of my apartment, the receiver cannot see the WAAS/EGNOS satellites in the southern sky. For those interested in setting up this GPS receiver for either navigation or timekeeping, the GPS 18x technical specification document, available from Garmin at [...] is of invaluable help, as well as the Garmin configuration software SNSRXCFG (Windows only, but supposedly works under WINE for Linux) which is available at the "Software" link at[...]. The out-of-the-box configuration for the GPS 18x was quite good, and I only changed a few settings with SNSRXCFG to reflect my specific needs (e.g. increasing the PPS duration from 100ms to 200ms, turning off the PPS signal if GPS lock was lost so that I don't inadvertently use bad timing information, etc.). Once I constructed the circuit board and soldered all the necessary components (about an hour or so), I simply followed the directions at [...] (specifically setting the "low_latency" flag with setserial, installing and configuring gpsd, and configuring NTP) and I had everything working in about 15 minutes. The GPSd software makes interfacing the GPS 18x with the computer trivial. After connecting the GPS to the computer and letting NTP run and stabilize for a few hours ntpq -p reported that the clock had an offset of 0.000 +- 0.003ms. That is, the clock was syncronized to the correct time with an uncertainty of three microseconds. That's excellent and about a thousand times better than using only internet timeservers. In short: this GPS receiver is well-suited for precision timekeeping and is quite inexpensive. A person with basic soldering skills can fabricate the necessary connector with little trouble. The configuration software from Garmin makes it very easy to change any settings on the device itself and the device is compatible with GPSd and NTP. If you're interested in GPS timekeeping this is almost certainly the best option. ##### Update Jan 28, 2012: I emailed Garmin with a few questions and they confirmed that unit only supports the L1 C/A GPS signal and WAAS/EGNOS-compatible augmentation systems. It does not support the new L2C or L5 signals, nor does it support Galileo or GLONASS. The modernized L1C signal transmitted by new GPS satellites will also support the existing L1 C/A signal, so existing receivers like this device will continue to work indefinitely. ##### Update Oct 13, 2012: I recently attended a conference in Germany and put this receiver on the roof of the car and connected the serial port to a laptop loaded with road navigation software. The magnetic base held it solidly in position at 160km/h (100mph) on the German autobahn. Such a mounting location resulted in a clear view of the sky at essentially all times: 10 GPS satellites were visible and tracked with a signal-to-noise ratio of 48-50 (which is excellent and extremely strong) for each satellite and excellent geometry (HDOP of 0.8). The unit was able to get EGNOS signal within a minute and estimated position uncertainty was 2.5 meters even while moving at 160km/h. The weather on the trip was poor and there was heavy rain: this did not affect the signal strength and the receiver remained waterproof along the whole journey. While the receiver is particularly suitable for timekeeping it is also quite satisfactory for navigation. ##### Update Oct 27, 2025: Everything is still working fine. I have several 18x LVCs that are in regular use and have been working fine for nearly 15 years. Although more advanced receivers are available, such as those that support other constellations like GLONASS (Russia), Galileo (EU), and Beidou (China) in addition to GPS (USA), have more channels (the 18x is 12-channels, I recently bought another receiver with 1,408 channels), support higher accuracy 1PPS precision (my u-blox M8T can do ~20 ns vs the 18x's 1000 ns precision), and have some additional useful features like specifying that it's in a fixed position, my 18x receivers continue to truck along without issue. The major advantage of the 18x is that it's a completely integrated unit that just needs wiring. Pretty much all other timing receivers are bare boards that need external wiring, cabling, etc. that add cost and hassle. For a general-purpose GPS receiver that also does really good timing, it's hard to go wrong with the 18x. Even though newer and better options are available, it's hard to go wrong with this one.

I have purchased many of these units over the years, and have never been let down. It has always exceeded my expectations for accuracy and performance. I first purchased this unit many years ago for an APRS tracker in a vehicle, and it worked for years stuck to the roof of a vehicle. It is fully waterproof. It has internal magnates, and says it's rated for something like 65MPH, but honestly, I don't think many vehicles could/would ever attain a speed that would peel this off a roof. It also has a spot for a bolt mount (also weatherproof) , if you want to get serious and bolt it down. It also does not appear to discolor paint, at least the paint on my vehicles. It has an internal rechargeable super capacitor or battery that retains date/time/almanac for some period of time being powered down, to help with acquisition upon power up. Because of this, it would always have very fast signal acquisition upon power up, always less than 1 minute, and sometimes just a matter of a few seconds, and worked everywhere, including many parking ramps (!!) and only failing to acquire signals in underground parking garages! After an extended power down of weeks or months, the internal power will run down, and expect it to take up to a few minutes to get a good fix. It survived summers, winters, car washes, etc, and never failed. I purchased several others for balloon mounted APRS trackers, and again, they worked well, where other GPS units would routinely have a hard time dealing with the massive signal refraction caused from the satellite signal bending effects of 120,000 cubic feet of hot air directly overhead from a hot air balloon envelope. Years later, several more were purchased due to the 1PPS out signal to create an array of several GPS timed NTP servers for some product development use, that proved to be so reliable, accurate and stabile, - greatly exceeding the reliability "enterprise" NTP GPS timed servers in our case, due to the fact that there are no separate antenna/cable/connector components that can be compromised by moisture/weather- that they were then retained past development for full commercial use in an enterprise setting. The waterproof hockey puck all in one design really can't be beat! Those units have been running 24X7X365 for many years, stuck to the roof of a metal building in the snow, rain, hail, sleet, ice, heat, sun, without any detectable known issues. All in all, if you need a WAAS enabled GPS unit for a project, this can't be beat. The only down side to these units is that you need to solder them to something (project board or connector) to use them, and you'll need a Windows PC with serial to run Garmin's configuration/firmware update utility if you want to change any of the unit's options (change baud rate, or change it to no 1PPS output if sat signal is lost, NEMA string output configuration, etc). The ones I've purchased always were advertised as connectionless, but they always came with a non weatherproof test connector/header that could easily be snipped off.

The Garmin 18x LVC is a bare lead OEM GPS unit with a measurement pulse output aligned to the Universal Coordinated Time (UTC) second, within a maximum error of 1.0 microsecond (1.0 millionth of a second) Only the LVC variety outputs the measurement pulse (Pulse Per Second) signal. As a retail item this unit is primarily used for very accurate timekeeping. One could theoretically use it for navigation, but with bare leads you need to solder a connector on the unit, and there are other 18x models, not the LVC, that have connectors from the factory. But the 18x models with connectors DO NOT output the precision measurement pulse, so they are useless as reference clocks. You may wonder why anyone would need a clock accurate to within 1.0 microsecond. The clocks inside computers are notoriously inaccurate, sometimes up to an hour off per day. So, the Internet is peppered with reference clocks. People interested in time keeping will place a reference clock server online, and thousands of Desktop PCs also connected to the Internet can poll these servers to accurately set their clocks. The reference clocks need to be accurate, because of dispersion in distribution (i.e it takes a small bit of time for the client PCs to receive the time from the time server. Having microsecond accurate time servers insures no client will ever drift past 1/2 second from UTC. It's all automated. The user doesn't do anything. It just happens. So that is what this particular unit is for, from a retail perspective. There is a web page, [...] , explaining in very simple terms how to make a time server. Soldering skills are required for individuals to make use this unit. The 18x USB, not the 18x LVC, is handy for navigation via a laptop.

It’s a good one.

Siempre un buen producto. Se acaban a la interperie, pero por supuesto que desquitan el costo. Bien Garmin !

Fa egregiamente il suo lavoro, con buona stabilità nella ricezione dei satelliti

I bought this to hook up to a yacht GPS Log. I should have checked the tech spec for the variant I needed. I wanted a 'wired' version - not one with USB connectors. This needs a 5V supply and the boat system is 12V. I bought a small 12V to 5V regualtor, connected it up and it worked fine. The housing looks as if it is waterproof, but I have installed it in a sheltered location. It would have been more straightforward if I had bought the PC version with an RS232 interface. Anyway, it does the job ok.