An Excellent Mapping GPS with NMEA 0183 Output AND Input for APRS Use
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When we started looking for a GPS unit for the Emergency Communications Jeep, we had one absolute must-have requirement. The GPS would have to support NMEA 0183 data output. NMEA 0183 data input would be nice as well. This is to facilitate something called APRS - Automatic Position Reporting System. This is a system used by HAM Radio Operators - and many in Search and Rescue - to keep track of position information via radio.
In APRS, you need a radio, a radio modem (called a Terminal Node Controller or TNC - it works just like a modem between a computer and a phone line, but in this case the phone line is a radio connection), and a GPS. The GPS is connected to the TNC via an RS-232 NMEA 0183 connection. The TNC takes the position information and formats it in a special way, it then triggers the radio and sends the position as a burst of data.
You can hear this by tuning a receiver to 144.390 MHz in just about any area in the USA. The bursts of data you hear are people transmitting their positions.
Some radios, such as the Kenwood TM-D700A we have in the Project Jeep, have the TNC units built-in. You just plug the GPS into the radio and it not only handles transmitting your position to other people, but it can also receive their positions. You can display their position information on the display screen on your radio, on an attached computer, or on the GPS unit itself if it will also accept NMEA 0183 data.
We checked out a number of units at the SEMA Show in Las Vegas. There were plenty to look at. The problem is that most manufacturers are trending towards units featuring "Turn-By-Turn" navigation where the GPS talks you through driving from one point to another. Units like this do not generally feature that NMEA 0183 connectivity we require. We even looked at a $2000 unit from Eclipse which lacked NMEA connectivity but had everything else.
We did find a unit from Lowrance which had what we were looking for, but even they are cutting back. Their older system actually had TWO NMEA 0183 ports. That would have been perfect as it would support an independent connection to the laptop in the Jeep, but one will do.
The Lowrance GlobalMap Baja 540C is a complete GPS system. It does NOT to turn-by-turn navigation. What it does is provide accurate position information, and it supports visual maps including Topographical information. It also allows you to search the map data for points of interest, gas stations, freeway exits, lakes, etc.
It's a two-part system, designed for both marine and land use.
The head unit - the Baja 540c - features a 5" TFT 480x480 color display screen and all of the functional controls. It's actually a very capable unit. It can even control a marine radar unit. But it isn't the GPS receiver. That's the second part.
The actual GPS receiver is a small puck unit, a 12-channel antenna/GPS/WAAS receiver unit called the LGC-Baja with a base that can be bolted onto just about any surface. The LGC-Baja is designed to a more rugged specification to survive real off-road use. It held up just fine in our testing.
It hooks up to what's called the NMEA-2000 bus. This is the latest in terms of interfacing marine-compatible navigational, radar, and even fish-finder systems. It uses one 15-foot pre-made cable to connect to the NMEA-2000 bus.
Installing the 540c system is a little more involved than most of the simple turn-by-turn units. Because you have a separate GPS antenna/receiver unit, there is a little more cabling involved. It's not rocket science, it's really quite easy.
To start with, you need to find a flat surface on which you can mount the LGC-Baja antenna/receiver. The top of our ARB Safari Snorkel turned out to be perfect for the task.
The cable coming off of the LGC-Baja is 15-feet long. It has a special red connector that goes to the rest of your NMEA-2000 gear. This is essentially a bus topology LAN. You have a central line, and this is tapped for each device connection. 120-Ohm terminators are used at the ends of this bus. All of the connectors are included. Both the LGC-Baja and the Baja 540c are tapped into this bus.
Physical installation of the 540c head unit involved finding a good location for the gimbal bracket included. It fit perfectly in our Project Jeep on the top of the center dash cowl. Routing the cables was then very easy - through the area behind the glove box and up to the center cowl. The red connector mates with the red connector on the back of the Baja 540c.
You then have to deal with a larger cable with a blue connector which you also connect to the back of the Baja-540c head unit. It features two sets of power connections - one to power the Baja 540c itself, the other to provide power to the devices on the NMEA-2000 bus. The connection for the NMEA-2000 bus requires a 3-amp fused circuit, and the one for the Baja 540c requires another. We setup these connections behind the glove box opening and put them up out of the way.
The same cable (blue connector) also has 4 wires which make up the RS-232 NMEA 0183 connection. Blue = unused, Yellow = Transmit Data out of the Baja 540c, Orange = Receive Data into the Baja 540c, and a shield wire. This was connected to the RS-232 GPS port on the Kenwood TM-D700A. I really wish they still included two ports on the Baja 540c, but that's the way the cookie crumbles. Anymore, we were lucky to find a GPS unit with one RS-232 port.
After the installation is complete and verified, you can power up. It takes a couple of minutes the first time to determine your position. Another good thing about the 540C is that turning off the 540c head unit does NOT kill the power to the LGC-Baja. Once it has a fix, it keeps it. Turning the head unit back on results in an instant display of your position.
The 540c head unit updates your position once each second. It will keep up to 10 trails with 9,999 points per trail. You can also save up to 100 routes. The display can be zoomed from as little as 0.02 miles across to 4000 miles across.
When you turn on the Baja 540c it contains a pre-loaded map of the USA and Hawaii. This shows major marine features and nav aids, and major metro-area freeways and larger roads. If you want more details and better maps, Lowrance offers several options. They offer their MapCreate software which allows you to make custom maps with extreme detail that can be loaded on to SD-type memory cards. These cards plug into a weather-resistant interface port on the front of the unit. We didn't have the chance to test that software, but I have seen a demo and it seemed pretty easy to use.
There are also maps pre-loaded on SD cards called FreedomMaps. These include the same details you can get from their software, and retail for around $100 each. We tested one for the Western USA and it was great! The backcountry data - complete with Jeep trails and 4WD roads - was excellent. For Search and Rescue, that's what we really needed. They include Topo data and work very well. We have had great luck with the one we tested in our 540c.
We did have one problem at first with the unit locking up when it was scrolling the map as we drove. A quick firmware update (available on-line from www.lowrance.com, simply download it and put it on an SD card with their auto-installer software) took care of that. Once that firmware update was installed, the 540c was absolutely rock solid.
The unit is easy to use, and you can find features, gas stations, and more using their search menus. The controls are large enough, and the menus are easy to navigate with a little practice. Their system is very logically organized, and you can memorize it easily. There is even a Man Overboard (MOB) function. Press the ZOUT and ZIN buttons and a waypoint is added and the course and bearing of that waypoint is displayed.
It has all of the other features you would expect, and a few you might not. One of the screens is a RADAR screen. If you have a marine radar connected to your NMEA-2000 bus (not likely in a land vehicle) you can monitor activity on the 540c display. Legalities aside, it would be interesting to mount one on top of a Jeep and take it out on the Bonneville Salt Flats to see what it does.
It will also show you what satellites you are seeing and where they are in the sky, and you can customize the data that you see at any time. You can overlay your ground speed, position, or just about any other piece of data that the 540c can provide. We usually keep the ground speed, battery/alternator voltage (detected through the power connection), and position on screen. I'll also put UTC on the display depending on the situation.
Since it can receive NMEA 0183 data, it can put icons on the screen (complete with the callsigns) of other APRS operators your radio hears on screen. This is PERFECT for Search and Rescue operations. It is also useful for interfacing to marine autonavigation systems.
One thing you will notice with many GPS units is that they radiate a quantity of HF noise. This won't generally bother you when running VHF or UHF, but you may pick them up with your HF radio gear. The 540c is no different, if we have our HF radio on we do pick up increased background noise. Turning the 540c head unit off eliminates most of it, and you can get that instant fix when you turn it back on. The noise can be bad, but it wasn't really worse than any other GPS units we have tested.
As for the display, it has several adjustable levels of brightness and has been completely readable in every condition we have been in, including with the top down. It's just the right size without being too big or too small. It fits right in with our other gear.
If I had to find one problem with the Lowrance system, I would have to say that some of their metro-area street data is a little behind. The street I live on is about 5 years old and does not show up on their maps yet - but it did on a couple of competing products. That's a little disappointing, but those competing products didn't feature the NMEA output that we needed. The Topo data and backcountry road and trail data is accurate and that's where we really need it.
You are looking at a retail price around $500 for the Lowrance Baja 540c system. It's not the least expensive unit out there, and it won't give you turn-by-turn navigation. What it will give you is a highly accurate GPS unit with an excellent display, NMEA 0183 output AND input, and the ability to take excellent Topo maps with an instant-on GPS fix. It was the perfect fit for our Search and Rescue Jeep.
James Bell, Jr.