Sunday, June 2, 2013

Lowrance Globalmap / LMS GPS Antenna Replacement Modification

The older Lowrance Globalmap and LMS series of marine electronics are terrific GPS receivers. The only common issue I see with them is that the GPS antenna units for them often go bad. The antenna are about 4" round white pucks that you mount high up on your boat that actually contains the GPS antenna / receiver along with an optional DGPS receiver. This then connects to the back of your Lowrance unit supplying power and communication to the antenna from the head unit itself.

There are two series of these GPS antennas depending on how new your Lowrance unit is. The older ones are NMEA-0183 based while the newer stuff is NMEA-2000 based (most models support both). The advantage of the older 0183 protocol is that is uses a simple RS-232 serial interface, while the 2000 protocol is CAN-bus based (not that this is bad, CAN is a great protocol, but for the point of interfacing these units the RS-232 protocol is significantly easier to work with). Both of my units (A Globalmap 3000 and LMS-480) support NMEA-0183.

Repairing the antennas themselves is a huge pain. I have a dead Lowrance LGC-3000 GPS CAN bus antenna that I cracked open to take a look inside, these units are definitely designed to not be opened, it took some serious cutting to get inside.

Inside Lowrance LGC3000

Nothing unexpected found, a basic GPS receiver, small micro, and an impressive watertight enclosure. Typically I see the micro and/or GPS receiver itself is dead. I'm not sure if heat is the cause or possibly static discharge is, but repairing usually isn't really feasible. Just getting into the thing pretty much destroys the nice water-tight enclosure.

So what to do if your GPS antenna is dead and don't want to spend $100+ for a new one? Simply use any GPS receiver that outputs NMEA-0183 data and feed it directly into the Lowrance spare serial port. This is pretty much every GPS receiver / module ever made.

Each device within the Lowrance family has an optional NMEA-0183 input (and sometimes output depending on device) that allows you to daisy-chain units together. So a single unit connected to the GPS antenna can send the GPS information via NMEA-0183 through multiple units allowing you to need only one antenna. Now the cool thing about this is in the Lowrance configuration menu, you can set which serial input you wish to receive the GPS information from along with what GPS strings you want to receive. This means you can feed NMEA-0183 GPS strings directly into the units spare serial input from any 0183 compatible receiver, not needing to use the Lowrance expensive antenna.

My solution as to use an old 12 channel Cirocomm receiver that I have had laying around which cost about $12. This receiver runs off of 3.3V- 5V and outputs TTL level NMEA-0183 GPS strings. The original GPS  module in the LGC puck can also be used as long as it is not dead itself. To use this with the Lowrance, I added an RS-232 level converter and small power supply to run directly off of 12V. I had these boards already designed and built for Xbee use, it was just a matter of wiring in the GPS unit to make it work. The only downside of this is you need to power the GPS unit directly as the Lowrance does not supply power on the spare serial interfaces like it does on the direct GPS interface. The serial interface requires only two wires, TX from the GPS antenna to RX on the Lowrance unit and ground. You could also interface this into the GPS input connector on the Lowrance, but if you are missing the antenna and cable, wiring to the spare serial interface avoids sourcing the expensive twist-lock connector. Once the new receiver is put together the only thing remaining to do is to mount it in a sealed watertight enclosure, something nice looking so it doesn't look stupid. Also preferably something plastic and white to reflect heat and be transparent to the GPS signal.

To use, set the Lowrance to use the NMEA-0183 input for GPS, then set the correct baud rate and GPS strings your receiver supports ($GPGGA and $GPGLL are the important ones). That is all, the Lowrance should respond indicating it is receiving GPS data and begin to populate you satellite information screen. Multiple units can then also be daisy-chained in the exact same manner.

Lowrance Globalmap 3000 NMEA Config
My Cirocomm GPS unit defaults to 4800 8N1, which is fine and sends $GPGLL, $GPGGA, $GPGSA, and $GPRMC strings, so make sure those are selected in the GPS configuration. If daisy-chaining, make sure the NMEA outputs are also enabled and set to the same baud rate on the sending units.

Lowrance LMS-480 NMEA Config
Note that again almost any GPS receiver can be used to supply GPS information to the Lowrance. Something like an old Garmin GPS 12 also works great as a spare if your antenna dies, simply take its NMEA-0183 output and feed it directly into the input of the Lowrance in the exact same manner.

Both units are daisy-chained off of my GPS receiver. Note testing was in my basement, so no GPS lock here


  1. I have a Lowrance Globalmap 5200c with a dead lgc-3000 antenna ( i believe this is NMEA 2000). What would be the easiest way to get it back up and running? Could i use an antenna with the older NMEA format?

  2. Tim,

    You can use any NMEA-0183 GPS antenna with the 5200c (including non-Lowrance brands). Check the 5200c manual as it will have wiring diagrams for the NMEA-0183 inputs. Aftermarket antennas will just need +12v, ground, and two wires to the Lowrance for GPS serial data.

  3. Brad, Interesting write-up on your Lowrance puck. I have a LGC-12W which has a Rockwell GPS receiver and antenna in the "puck" and outputs Zodiac binary to my LCX-18C chartplotter. The GPS no longer seems to be sending any sat data to the plotter. Not sure if its the antenna or the receiver that is bad. Disconnected from the chartplotter and powered from an external 12 VDC supply, the puck only draws 35mA, which seems low. Monitoring the data lines when plugged into the plotter the puck sends back a series of repeating pulse trains with one pulse being 700 msec long and then four 460 ms pulse. The plotter sends out a series of pulses to the puck when first turned on. All this is seen on my scope as I have not managed to find a way to decode the zodiac binary data yet.
    What method did you use to open your puck?
    Do you have any experience decoding this type of data?
    Any hints on troubleshooting?

    1. Mitch,

      It is hard to say what is coming out of your LGC-12W based on the description, the 12W is similar to the LGC-2000 I believe. if you have a logic analyzer you could at least verify the data is valid. It should still be outputting NMEA-0183 information, typically $GGA and $GSA strings regardless of the propitiatory Rockwell protocols.

      I cut mine open with a hacksaw around the lip of the puck, but it pretty much does destroy it in the process. If you have any other device that can output NMEA-0183 serial data you could at least verify if either the Lowrance chartplotter or puck has an issue. There is free NMEA emulator software available that should be able to validate this for you. My guess is the LGC-12W is toast. It's probably sending the NMEA headers but no valid position data along with it.


  4. Thanks for getting back to me. I have been traveling, so please excuse the


    I finally got around to opening the puck (managed to pry it open without too

    much collateral damage) and found that it must be a very recent version of the

    LGC-12W because it looks exactly like your LGC-3000! The spec from Lowrance

    listed the chips as Rockwell, but there is actually a SiRF II /LP chip set in

    there. That along with 8M of memory, a voltage converter and a MAX 232 chip.

    So, it does not speak Zodiac binary as reported! I confirmed op of the head

    unit by feeding NMEA data from a simulator, as you suggested and it worked

    fine! My head unit actually has a GPS port as well as a larger 2 Input/1

    output NMEA port, and I tested the former, which is used to power and 'talk'

    to the LGC-12W. I also connected the LGC to a PC running VisualGPS and saw the

    stream of NMEA (standard GGA,GSA/V, RMC and some apparently Lowrance strings

    ($LAWREV).) No fixes seen or satellites detected, though it -30C here and I

    don't want to spend too much time outside!!!

    Anyway the testing goes on and I'll let you know how it turns out!

    BTW, I noticed one of your blogs about re-capping your Tek 2445B. I have a

    2445A and re-capped last year. Love that scope!



  5. I am going to connect my Lowrance lcx/20c to a VK16U6 GPS module and antenna ttl signal,
    via the nmea0183 I have a Blue, Yellow and Orange Cable Plus the Shield or gnd.
    I understand the following Orange is TX or Tranmitt, Yellow is RX or Receive the shield is GND and the blue is not used.

    This VK16U6 GPS module needs 3 to 5 VDC can you tell ne where to get this voltage or how....



  6. Hi Oscar,

    My LGC-12W module has a power supply inside that takes the 12 volts supplied by my LCX-18C and converts it to 3.3 volts. this should power you VK16U6 GPS module.


  7. Hi Brad,

    Am I successfully leaving messages on your blog? First time user so not sure if I am doing it right! I have posted 2 comments over the past month and no reply.


  8. Desde Galicia.
    Gracias por tu interesante artículo.
    Saludos cordiales.

  9. Hi,
    I'm trying to us a Globalsat BU-353 (USB) as the antenna/receiver for my LMS 240. I'm not very techie and have no test equipment except a multi meter. I've tried wiring in through the original puck plug and the spare COM port, but get the "GPS Module not responding" message. Maybe a dumb question, but do I need to do something different since it's a USB device?

    Thanks, Jeff

  10. I have a Lowrance Globalmap 2000. The Monitor is dying. What can I do to get it running again, or where can I get a replacement?

  11. HI Brad, I have a globalmap 7200c an trying to wire an Eagle EGC 12W antenna (puck) onto the Globalmap unit. I am encouraged by your blog that it is possible to wire it up to the Nmea 0183 cables. My question is the EGC 12w has 4 pins and I assume wires (1-power, 2- ground, 3- XMT gps and 4- Rec Gps). Can you show me which wires from the EGC12w joins up with which coloured wire of the NMEA 0183 loom (set up as RS 232)? thanks

  12. Try the Sirf 3 gps receiver on ebay uk, wiring details sent by seller.

  13. I have a Lowrance LMS332C and the LGC2000 antenna died. I decided to upgrade to a newer unit rather than pay thru nose for a new used antenna. I did however, as you suggested, buy a very inexpensive new antenna that I was hoping I could connect to it and have work then just sell the whole thing. My wiring looks the same as the LGC3000 in your picture. Can you tell me what color corresponds with what pin #? I am assuming red is hot and black is ground. I want to reuse my blue connector that goes to the network port.

    1. Hi. Were you able to find the pin sequence for the lgc 2000? Someone cut the end off the antennas. It has 5 wires including the ground, however, I cannot find any pin diagrams or anything related.b