I don't know what COM Port my GPS is connected to. What should I do?

Electronics Hookup and Configuration

There are 5 types of connections between a GPS and the computer:


1. Standard Serial Connection
For a Standard Serial Connection, the GPS is transmitting NMEA data at 4800 Baud over a serial cable. This cable is connected to a "DB9" connector on the back of the PC - which looks like a "D" with 9 pins (or sockets.) This is the most common installation on older "desktop" style PCs and older GPS units.

2. Serial GPS connected to a USB-to-Serial adapter
In this connection, the Serial Connection (DB9 - described above) from the GPS is mated with a USB-to-Serial adapter that converts the signal into a USB connection. The USB connection is flat and commonly used to interface with mice, printers, digital cameras, and many other computer accessories. Since most laptops lack standard serial connections, this is a common option for navigators using an older GPS.

3. USB (or Bluetooth) GPS antenna connected directly to the PC via a Virtual COM port.
Today, most GPS's used for live positioning are USB GPS antenna units. These are often the size of a PC mouse (or smaller) and feature a USB cable that connects directly into the computer. There are many popular models - an Internet search of "GPS Mouse" will yield many choices. Some laptop/tablet computers even have these sort of GPS' built into the device.

4. USB (or Bluetooth) GPS antenna connected directly to the PC via Windows Location Services.
In some cases (usually with Windows 10-based PCs), USB/Bluetooth/Built-in GPS devices do not use Virtual COM ports to transmit the GPS signal to other applications. Instead, these GPSs use Windows 'Location Services' solely to transmit the GPS signal throughout the operating system. At this time, TNP is not directly compatible with these GPS units. However, there are third-party applications that will convert the Location Services GPS positioning data to a virtual COM port/NMEA. These applications include "GpsGate Splitter" - https://gpsgate.com/products/gpsgate_client ; use it to create a virtual COM port, then your GPS can connect to TNP in that fashion.

5. Garmin Handheld GPS connected to the PC
Garmin offers a line of handheld GPS units (such as the GPSMap 62/64, or Oregon/Montana) that connect to the computer via the USB Port. These interface to the PC in a fashion unlike the other three connection types listed above. As such, they are not the subject of this knowledge base article. Instead, please refer to Connecting a Garmin USB GPS.


With the exception of handheld Garmin GPS units that connect via USB, Terrain Navigator Pro interfaces with the GPS through the use of a "COM Port". This may be a physical connector on the back of the PC, or a virtual connection provided through a software driver.


I have a Standard Serial Connection. How do I determine the COM Port the GPS is connected to?
The easiest way to determine the COM port is to use MTTTY to verify that a NMEA data stream is being received by the computer from the GPS. To do this, set the GPS in NMEA interface mode (most GPSs are always in NMEA Interface mode, only those offered by Garmin may have other modes.) Then, refer to: Using MTTTY to test and verify the GPS connection

Once you have determined the COM Port, enter this value into the GPS Setup screen of Terrain Navigator to connect to the GPS. In TNP, open the GPS menu, choose Setup, set the manufacturer to NMEA - generic, the Unit to NMEA 0183 and set the Port accordingly. You also may need to determine the Baud rate used by the GPS, and enter it in TNP's GPS Setup, Port Settings.

I have a Serial GPS connected to a USB-to-Serial adapter. How do I determine the COM Port the GPS is connected to?
All USB-to-Serial adapters require software drivers to operate. Thus, a software driver CD-ROM accompanied your adapter. If the CD was missing or has been lost, download the driver from the manufacturer's web site. Once the driver has been installed, click here to determine the virtual COM Port of a USB to Serial Adapter.

Once you have determined the COM Port, enter this value into the GPS Setup screen of Terrain Navigator to connect to the GPS as described above.

I have a USB GPS antenna only connected directly to the PC. (Or connected via Bluetooth, or built into the PC.) How do I determine the COM Port the GPS is connected to?
All USB GPS antennas require software drivers to operate. Thus, a software driver CD-ROM accompanied your GPS. If the CD was missing or has been lost, download the driver from the manufacturer's web site. Once the driver has been installed, it functions identically to a GPS connected through a USB-to-Serial adapter; click here to determine the number of this type of virtual COM Port.

One exception to this are GPS units whose drivers do not create a virtual COM port. Instead, these units connect solely to the computer's operating system using Windows Location Services. This is usually the case on PCs that are running the Windows 10 operating system. These GPS units require a third party application (such as "GpsGate Splitter" https://gpsgate.com/products/gpsgate_client ) to create a virtual COM port which is, in turn, compatible with Terrain Navigator Pro.

Once you have determined the COM Port, enter this value into the GPS Setup screen of Terrain Navigator Pro to connect to the GPS as described above.

Finishing the Job: Reading the GPS Stream in Terrain Navigator Pro

To set TNP to connect to the GPS:
  1. From the 'GPS' menu, choose 'GPS Setup Wizard'. 
  2. Follow the on-screen instructions.
  3. If the GPS Wizard can not detect the GPS, select 'Setup' from the 'GPS' menu. Set the 'Manufacturer' to 'NMEA - generic', set the Unit to 'NMEA 0183' and specify the COM port determined during the above tests. Also, ensure that the correct baud rate of the GPS is selected in Port Settings. Then press 'Close'.
  4. Once the signal is detected, choose 'GPS Tracking', 'Start Tracking' from the 'GPS' menu.

Related Knowledge Base Article:
Configuring Terrain Navigator Pro to the GPS - Basic Instructions.

Feedback and Knowledge Base