GPS Receiver FAQ

This page contains all information necessary to get a compatible gps receiver to work with Navgps.

What are the requirements of the gps receiver?
What receivers are compatible?
What receivers are incompatible?
Which receivers are recommended/not recommended?
How do I connect the receiver to my handheld?
How do I connect the receiver to my laptop/pc?
How do I configure Navgps & the gps-receiver to communicate?
How do I know everything is ok?
I still got do I troubleshoot?

What are the requirements of the gps receiver?
The gps receiver has to be compatible with the NMEA protocol.
In plain English, what this means is that you have to check the specs for the gps model you're interested in and make sure somewhere in there is the word 'NMEA'.

Another detail is that Navgps uses two specific NMEA messages - $GPRMC and $GPGGA (see trouble-shooting section below for more info). You need to check the specs to make sure that these two commands are supported. Again, these are elementary messages and most units supporting NMEA, should support these messages.

What receivers are compatible?
Any receiver that meets the above requirements is compatible with Navgps. That means that except for the very inexpensive trekking type units, it should work with virtually any unit out there.

Even though we cannot compile a full list because of the variety and amount of different models out there, through self-test and user feedback, we've determined Navgps to be compatible at the very least with the following:

  • Lowrance Airmap 100
  • Pharos GPS - both cable and Compact Flash version
  • Magellan 300 series
  • Garmin III
  • Garmin 195
  • Navman - download driver here and set the Navgps port and speed to COM4 or COM5 and 57600 respectively.
  • DeLorme Tripmate
  • Teletype/Pharos Compact-Flash Card

What receivers are incompatible?
It's not compatible with the following:

  • DeLorme Earthmate - it does not output NMEA. But if you already have one and would like to use it, Byonics makes a cable dongle that'll translate it to make it Navgps compatible - it's called GST-1.

What receivers are recommended/not recommended?
After trying out various units, we'd say that the Navman is not a good aviation-use receiver.

The Pharos is generally better - but looses track when you suddenly change pitch or bank and only a reset brings it back to normal operation.

Most Garmin handhelds do quite well.

Also the Pretec compact-flash unit performs very well - but the antenna is required.

How do I connect the receiver to my handheld?
For most configurations, you'll need three connectors

  • A serial cable for your handheld. Usually from the handheld manufacturer.
  • A serial cable for your gps unit. Usually from the gps manufacturer.
  • You'll find that you cannot connect the two cables together - both the above cables have female ends. To make the final connection, you'll need a 9-pin male-to-male null-modem connector (see picture at left). If they just have a male-to-female null-modem connector, then you'll also have to tack on a male-to-male connector. The folks at Radio Shack should know all about this.

Connect all three/four together and you should be set.

Some gps receivers (namely the Pharos), come with handheld specific cables - making the setup easier and cleaner.

Compaq IPAQ Users:
Compaq has just come out with a cable that should make the connection much easier and cleaner. Click here for the Compaq RS-232 Cable.

You just need this cable and the cable from your gps vendor - no need for null-modems etc.

GPS Cables:
For cables of all kinds to connect gps units to laptops/pdas - recommend

How do I connect the receiver to my laptop/pc?

Assuming that your laptop has a serial port, all you just need a serial cable from the gps manufacturer.

How do I configure Navgps/receiver to communicate?
Once the cable connections are made, it's time to configure the gps receiver and Navgps.

Depending on your receiver (read the manual), set the receiver unit so that it's communicating at a given speed - 4800 bps (bits-per-second) is good. Other communication parameters should be parity=none, char-size=8, stop-bits=1. These are industry standard and should be the default.

On some units without a screen display, you cannot configure the unit. For example, the Tripmate and the Pharos. They use the default speed of 4800 bps.

Start up Navgps and select Preferences from the Options menu. Select the communication port and the speed you selected for the receiver unit. For handheld users, the port is almost always COM1. Click Ok.

How do I know everything is ok?
Once you click ok and you have the gps receiver powered on and the cable is connected....after some time you'll see the message 'Locating Satellites...'.

Sometime after that you should see the moving map centered at your current location. You're set to go!

Note that some receivers, when being initialized for the first time after battery change will take a while to locate the satellites.

I still got do I troubleshoot?
First read the above sections on the cable configuration and setting up the software. If problems still persist...then it's time to roll up your sleeves and troubleshoot.

Below are progressive messages you'll see. If the messages are stuck at one particular one - you have to solve that first before moving on.

Does your handheld freeze or become very slow when the serial cable is attached?
Make sure you don't have any software that uses the serial port. Case in point might be keyboard hardware that connect via the serial port. Remove/disable any such software.
Navgps had been written to handle any data coming over the serial line - whether correct or incorrect. It should not freeze without an external interference.

Do you see the message 'No GPS Rcvr Activity'?
If yes...that means that no data is being received from the unit.
Make sure the cable connections are correct and tight.
Make sure the receiver is outputting NMEA messages.
Make sure the port you selected in Navgps, is the one the cable is connected to.
If you're technically savvy, you might want to connect the receiver directly to the PC (disconnect the null-modem) and run a terminal program on the desktop and see what messages are coming over. Note the communication speed.

Do you see the message 'Waiting for NMEA Data'?
If yes...that means that some data is being received, but is not being recognized as valid NMEA messages. Two things could cause this:
The gps receiver is not outputting true NMEA messages.
The communication speed (baud-rate) selected in Navgps is not the same as that set in the gps receiver unit. This is more likely. Make sure the same speed is being used for sending and receiving.

Do you see the message 'Waiting for NMEA gprmc'?
Do you see the message 'Waiting for NMEA gpgga'?

If yes...that means that these required NMEA message is not being received. On some gps receiver units, you also have to enable the transmission of message types individually. Otherwise, you'll have to check the gps receiver manual and make sure that these messages are supported.

Do you see the message 'Locating Satellites...'?
You should be here, if you didn't see any of the messages above. This is a good sign. Just be sure you're in an open area for the receiver to lock-on to the satellites.

Be advised that if you're initialiazing a new gps (or after battery replacement), this could take a while. Units can take up to 15 minutes to locate the satellites.

If you're still not able to lock on to the satellites, then please contact us.