• Revision 2/2/97 - (see mountain performance & antenna connector, ... )
• Revision 2/7/97 - (Ext. Ant, Current Draw, Dead Reckoning, Data Smoothing, ... )
• Revision 6/29/98-(New hardware platform, CityPoint database)
• Revision 3/8/99 - (Incorporate G-12CX Color GPS feature differences)
• Revision 3/28/99-(Review by Bob Kaemmerer)
• Revision 12/23/01-(Ver. 4.57 adds area-calculation feature)

After a couple of years enjoying a 12xl, I recently acquired a 12cx, it is a really sweet machine. Good sensitivity, good features, impressive city data base, lots of track log, etc. The display is OK, wouldn't give it a great rating, but  colors do enhance the information content. If you don't look at it straight on, things get hard to read. And just like the xl, when the display is hot (from laying on a dashboard) the display gets darkish and loses contrast. 

I noticed that the "Power Save" feature has returned, I last saw it on the 45xl. This feature has been active on the 12cx during the above observations, wonder what it would be like if it was off? The 12 cx has an elapsed (ELPSD) time counter so I can measure the battery life accurately.  Note that there is also a 'TTIME" counter, this counter appears to increment only when it thinks you are moving, so don't use this counter for batt life measurement. 

A negative observation: the satellite status bars no longer distinguish between active sats (solid bars) and acquiring sats (hollow bars) so I can't tell which sats are doing the work. 

A curiosity: when I first got the unit, there was a number displayed on the lower right-hand side of the sat display page that indicated the DOP for the current conditions. Also there was a small number displayed on the position page in the time 'window' it was presented in a time format and appeared to be equivalent to the 'elapsed' time counter. After a few hours usage, these numbers disappeared?? Anyone know how to get them back, the DOP is especially useful. 
Bob Kaemmerer

Comments by Timothy J. Lipetz: 

I found a store that had both the XL and CX, and I compared them.  At first I thought the CX looked better, but then I noticed that was only from a narrow viewing angle.  When viewed from outside that viewing angle the 12XL was MUCH EASIER TO SEE, and the 12CX's screen became almost unreadable. 

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The temperature range for the G-12CX is narrower than for the G-12XL: 
        5°F to 131°F (-15°C to 55°C) for the G-12CX 
        5°F to 158°F (-15°C to 70°C) for the G-12XL 
The button layout on the G-12CX has also changed to incorporate dedicated zoom in/out keys and the rocker keypad is now round.  Otherwise,  please read the following review to be for the G-12CX as well as for the G-12XL.

The Garmin G-12xl continues to be improved beyond the first G-12xl units delivered 18 months ago.  The latest edition with firmware versions 4.0x and up include enhancements such as 24 hour battery life,  built in CityPoint database (over 22,500 towns and cities in the USA alone).  

Area calculations of an enclosed track became available in the 4.57 update. The unit draws a line from the beginning to end of track to enclose the area.  Units available are sq ft, sq yd, acres, sq mi, sq nm, sq mt, sq km, and "Auto."  If one travels in a figure-8 manner, one area is subtracted from another.  If one travels in two circles in the same or opposite direction at the same location, the two areas are added together. 

Lets review features and operation. Most of the features are the same as the Garmin G-II+ and G-48 marine units. 

The G-12XL does lock to the SV signals quickly. From a "cold" start, after a 2000 mile UPS trip, it locked on in 56 seconds. After a 3 hour off time, the lock up time was 20 seconds. Specifications are "warm start" , 15 seconds, "cold start" 45 seconds, "autolocate" 5 minutes.  A popular feature  is the "Initialize by Country" feature.  With this feature, you may select your country from a list and it will speed up the Autolocate from an unknown location. 

The G-12XL's specification for position accuracy is 100 meters with SA, 15 meters exclusive of SA and 5 meters with suitable DGPS correction signals. This is considerably better than the DGPS specs available with most low cost single and dual channel multiplexing systems. The DGPS error specification for the G-45XL for instance is 10 meters. This reduced error capabilities are achievable with even low cost multichannel receivers as compared with single and dual channel units. An averaging mode is available in the G-12XL to improve waypoint 
accuracy in the presence of SA. I have observed error estimations in the range of 50 ft with a few minutes of averaging at a spot.  David Wilson has tested the G-12xl and other GPS receivers in a controlled environment to determine absolute accuracy.  See: ACCURACY OF GPS RECEIVERS for more information. 

The G-12XL operates from 4 AA batteries or from external power in the range of 10 to 40 volts DC. External current draw (version 3.5x and later) is about 80 ma (light off) and 120 ma (light on). Twenty four  hours is specified as the AA battery life. Some report AA battery life up to 28 hours on highest quality AA alkalines.   The data/power cable used is the same as the Garmin G-45xl/G-II+/G-III/SP units. The external antenna connector a miniature MCX coax jack is located on the rear of the unit just behind the "up arrow" button. A six inch adapter lead MCX to BNC jack is available for US$20. We measured 4.35 volts on the connector with battery voltage measuring 5.05vdc on the G-12XL's test screen. The Garmin GA-26 amplified antenna, the Lowe amplified antenna,  and the Magellan M-4000 amplified antenna all work with the G-12XL (with adapter cable). We believe most other 
amplified GPS antennas will work as well. The G-12XL has a diode switch to disable the internal antenna (to prevent interaction) when the external antenna draws power (unlike the Magellan GPS-X000xls). 

The unit outputs NMEA protocol 0183 ver 2.0. Other proprietary sentences are output as well. DGPS signals in the RTCM-104 format are accepted. A setup screen permits selection of the I/O combination needed by a particular application. 

The G-12XL has a number of features and displays that are useful. These include:

You can "point" at a waypoint on the map and the distance and bearing to that waypoint from your present position will be displayed. You can also "mark" and store a new waypoint by moving the cursor to the desired position on the map and pressing the MARK key plus ENTER. The map may be north up, or current track up, or direction of current route segment up. The map display can contain position range rings, plot straight lines between waypoints, display "nearest" nine waypoints, or put names beside waypoints. The map screen also supports zoom and pan features.  Sixteen ICONS are provided to identify waypoints.

Jack Yeazel and I have been out testing the 12XL on the road and in the field. The G-12XL has worked without a flaw that either of us could find. We uploaded and downloaded waypoints, tracks and routes using Waypoint+ (W95), and G7to..(DOS). We tried it out on SA4 and Delorme MapExpert, and Vista. No problems found. We compared the G-12xl with the EE, and G-II+.  In a sentence, the 12XL on a par with the other two other two in every test for lock stability, multipath performance, re-lock after an underpass, and ability to suddenly change direction without loss of lock. We were very impressed. We also  tried the G-12XL (barefoot [antenna wise]) on the dash with a G-45 with external amplified antenna mounted to the windshield.  The G-12XL outperformed the G-45 in every test. We were very impressed at the speed that the speed the G-12XL responded to changes in direction as compared to the other two units. At about 4 mph, the 12XL,  and G-II+  would complete a change of direction in about 15 feet. The G-12XL laid down smooth tracks on our highway maps during all tests. No gaps, jumps, etc., (The G-12XL has data smoothing.) The G-45 had a number of minor jumps of perhaps a few hundred feet at most in multipath situations. The latest G-12xl is (slightly) more sensitive than earlier G-12xl units.  Garmin says this is a result of continuous small improvements in RF component quality. 

These are the major features We have observed in playing with the G-12XL. Our impressions are that the G-12XL is an improved G-45XL with a much faster acquisition of satellites and a well thought out user interface. There are a few additional features that will appeal to many, particularly the improved (12 channel) receiver performance and quicker lock. The more frequently used display items are easy to use, but the more obscure require several screens and menus and half a dozen button pushes to access. All in all, We like the unit much better than the older single and dual channel units we have tested. 

We made these tests using two Toshiba 2150C laptop computers both running moving map software. The two gps units were operated simultaneously on the dash in front of the driver (G-12XL) and with amplified external antenna on the lower part of the windshield in front of the passenger (G-45). The laptops were positioned so both displays could be watched simultaneously and then we drove over a course of perhaps 30 miles and evaluated the relative performance of the GPS equipment by observations including the GPS "cookie trails' on the moving map display. Dropouts of the G-45 for instance would show a break or jump off the track of the "cookies" for that unit. 

More Field Tests (2/1/97): I took the G-12XL into the North Georgia mountains where I have previously had problems with my M-4000. The improvement in performance evident in the G-12XL is substantial. We drove for about 4 hours in twisty mountain roads with switchbacks and steep mountains on the side of the road. The M-4000 would frequently lose lock and take up to minutes to recover. The G-12XL never lost lock as long as it was laid flat on the dash of the car. The G-12XL produces position output to the computer much faster than the M-4000. With the M-4000, the position indicated on the computer map usually follows behind actual position by 200 to 300 feet making you unsure if the next road intersection is the one you want. With the G-12XL, points plotted on the display about every two seconds and seemed to be only perhaps 50 ft behind the actual location at the moment of plot. Several times, just before we entered a switch back, I removed the G-12XL from the dash and put my hand across the antenna to block sigs. Then after the switchback, I put the G-12XL back on the dash. Within less than 5 seconds, the G-12XL recovered lock. In similar tests, the M-4000 required up to a couple of minutes to recover lock. Multi-Channel Parallel GPS receivers have MY vote! A couple of EE owners have reported that the EE would work on the seat of the car beside them. I tried this out with the G-12XL for a short time. Perfect operation did not occur. However, it did provide a track almost all of the time, but sometimes, switchbacks would interrupt proper tracking for 10 to 20 seconds. There were 6 to 8 sats visible while I was running the "on the seat" test, still.. Not Bad! Actually, this is superior performance. Also, multipath caused additional position errors in the range of perhaps 200 feet SOME OF THE TIME when the G-12XL was located on the seat instead of the dash. When I put the G-12XL back on the dash, the track would immediately come back to normal error. Therefore, if you are interested in accuracy, the dash is the better location. An outside antenna would be even better. My hat is off to the EE in this regard as well since it is reported to provide similar performance. With the Garmin G-12XL, I don't think I will need to carry my amplified external antenna around anymore. Operation on an automobile dashboard appears to give 100% satisfactory operation. 

We also noted that both the G-45XL and the G-12XL have a form of "dead reckoning" for moments when signal dropouts occur. For instance, if the G-12XL is tracking along and just before a sharp turn you invert it and block its antenna, it will continue to track straight for about 30 seconds. It also provides a very good data smoothing filter to throw out random fixes that are way off track. This results in an exceptionally smooth track on a moving map display even when multipath is present. Even with this filter, there was no overshoot apparent during quick stops, sharp turns, and similar maneuvers when normal continuous tracking was taking place.