Garmin 18x LVC GPS Navigator Unit

I have the Garmin 18x LVC GPS attached to a serial card installed in a Debian Linux 'Squeeze' box (which was configured using the Setserial, GPSD, and NTP packages).USB based GPS units are useless for accurately setting the time.The 18x LVC GPS unit requires 5 volts of power (red wire), and for this I use a specific serial card, the StarTech.com 1 Port PCI RS232 Powered Serial Adapter Card (PCI1S650PW). The card can be configured to supply either 5 or 12 volts (or none) on pin 9 of the RS-232 DB-9 connector, and can draw power either from the PCI bus itself or from the PC power supply directly via the onboard Molex floppy power connector. (I used the latter option). Once the jumpers had been set and the card installed no drivers were required for Debian, Setserial recognizing the card as having a 16550A UART with a baud base of 921600.The GPS unit itself is mounted externally on the chimney, as the GPS satellite signals are fairly weak, so installing outside is the best option as the GPS itself is weatherproof. For me, this location gives the GPS a clear view of the sky, but the 5 meter (16 feet) cable would not be long enough to reach the computer inside the house, so I replaced almost all of the original serial cable (which is molded onto the 18x LVC). The wires (especially the three signal wires, which includes the PPS) are also *VERY* thin. So, I cut the original cable close to the GPS unit itself and extended it with my own cable which runs all the way back to the computer and is terminated with a serial DB-9 connector. If you do this, remember to use a shielded cable. There are basically five wires needed for the serial connection: Measurement pulse output (PPS) from the GPS is yellow -> pin 1 (DCD) on the DB-9, transmit is white -> pin 2 (RXD), receive is green -> pin 3 (TXD), ground is black -> pin 5 (GND), and power is red -> pin 9. For the replacement I used a shielded CAT 6 cable and joined each of the pairs together at both ends and used these to give me four of the connections: PPS, transmit, receive, and power (90 mA). I then connected all of the black wires together at the GPS end of the cable and used the drain wire as the ground, connecting it to pin 5 on the DB-9 at the other end. For mounting there is a metric (M3) threaded brass recess on the underside of the 18x LVC.I also have the StarTech.com PEX1S553LP 1 Port Low Profile Native RS232 PCI Express Serial Card with 16550 UART card installed in a Windows 7 PC which is only used to run firmware updates, etc. on the GPS when needed (as these cannot be performed under Linux). My 18x LVC is updated to version 3.80 (26th March, 2012). For what it's worth, my time1 setting in ntp.conf is 0.035. This gives me the lowest offset and jitter for PPS.Works like a charm, with extremely low latency PPS time (accurate to a few microseconds).

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.