This question is often asked with regards to Raveon’s GPS tracking transponders. This tech blog describes how to determine your GPS transponder’s locations and addresses some additional questions.

The short answer

The NMEAOUT 1 command will enable output of NMEA 0183 compliant messages on the serial port. This will work on any GPS-enabled Raveon radio (M7 GX, ATLAS PL, etc). After exiting command mode, you’ll see the GPS transponder outputting messages similar to the following:

$GPGLL,3308.35228,N,11716.16936,W,213357.00,A,A*77
$GPGGA,213357.00,3308.35228,N,11716.16936,W,1,07,1.06,00134,M,-035,M,,*5F
$GPRMC,213357.00,A,3308.35228,N,11716.16936,W,000.8,277.0,040512,12.0,E,A*10
$GPGLL,3308.35218,N,11716.16947,W,213402.00,A,A*75
$GPGGA,213402.00,3308.35218,N,11716.16947,W,1,06,1.14,00135,M,-035,M,,*5E
$GPRMC,213402.00,A,3308.35218,N,11716.16947,W,000.4,254.1,040512,12.0,E,A*1E
$GPGLL,3308.35232,N,11716.16968,W,213407.00,A,A*75
$GPGGA,213407.00,3308.35232,N,11716.16968,W,1,06,1.21,00136,M,-035,M,,*5B
$GPRMC,213407.00,A,3308.35232,N,11716.16968,W,001.1,271.2,040512,12.0,E,A*1E

You probably noticed the GPS coordinates in the messages above. That’s Raveon in San Diego. In this example, there are typically 3 types of NMEA messages (RMC, GGA, and GLL) that the trasponder will periodicallly output. The NMEAMASK command in the Raveon GPS transponder can be used to enable/disable the various NMEA messages. The NMEARATE command can be used to configure how often these commands will be sent out the serial port.

GLL

The $GPGLL message is the simplest NMEA message to use (although they all contain position information). Its NMEA GLL format is:
$GPGLL,<Latitude>,<North/South>,<Longitude>,<East/West>,<UTC Seconds>,<Valid Data>,<Autonomous Mode>*<Checksum>
The possible values for <Valid Data> are “A” when the data is valid and “V” when it is invalid. <Autonomous Mode> is always set to “A” on Raveon radios.

GGA

$GPGGA,<Latitude>,<North/South>,<Longitude>,<East/West>,<GPS signal quality>,<Number of Satellites>,<Horizontal DOP>,<Number of Satellites>,<Altitude>,<Units>,<Geodial separation>,<Units>,<Age of diff GPS data>,<Reference ID>*<Checksum>
The GGA message is included because it contains the altitude information. The altitude field in Raveon products is always in meters.

RMC

$GPRMC,<Latitude>,<North/South>,<Longitude>,<East/West>,<Speed>,<Track>,<Date>,<UTC Date>,<Magnetic Variation;,<E/W>*<Checksum>
The RMC message contains the track/heading and ground speed information.

Why not $PRAVE?

$PRAVE is a special Raveon format that is intended for use with over-the-air position updates. It differs from a standard $GPGLL (or GGA or RMC) in that it also contains flags, addresses and signal strengths specific to Raveon GPS trackers. A number of the fields are not applicable for a message that wasn’t sent over-the-air.
Messages comming out of the Raveon GPS Transponder that begin with $PRAVE are due to the reception of an over-the-air message from another GPS transponder.

Parsing the $PRAVE message

The messages output by enabling the NMEAOUT switch are standard NMEA GPS messages. There are many open source and licensed parsing libraries available. The $PRAVE message format is a NMEA compliant “private message” (the $P indicates this) and most third-party parsers are able to parse it.

Raveon has VB, C and C++ example code that can parse NMEA messages, so contact Raveon tech suport if you would like copies of this code.

The RavTrack Atlas PL personal GPS locator radio network capabilities

Most people will identify the Atlas PL personal locator as an excellent device for people to wear and to send GPS position information, alerts, and man-down status.  Typically the Atlas PL is used in conjunction with the RavTrack AVL GPS vehicle transponders which are equipped in fleet vehicles and used for base receiving stations as well as store-and-forward repeaters.  It is common for these latter transponders to be used to complete a GPS tracking radio network for tracking both personnel, and vehicles, or other costly assets.

However, it is also possible for the Atlas PL units alone to be used to construct a GPS tracking network complete with multiple base stations and/or a repeater, without the involvement of the vehicle transponder models in the system.  The Atlas PL inherently has all the capabilities of the vehicle based models.  Releasing these capabilities is simply a matter of following correct configuration procedures for the Atlas PL.

The following diagram demonstrates the use of the Atlas PL in its traditional role as a personal GPS transponder but also as multiple base stations, with one base station also serving as a repeater.

Within each box are typical settings of the Atlas PL as part of the GPS tracking scheme.  Above each box are the intended uses of each Atlas PL in the tracking network, while below each box are a series of configuration commands the user should issue to each Atlas PL unit to configure each unit for the particular use specified.  Finally, alongside each command is an indication of what that command actually configures in the Atlas PL.

Each Atlas PL starts out in GPS mode 8.  This configures the Atlas PL to function in the most common transponder configuration and enables the advanced battery management functions of the Atlas PL as well.  However, it is important to note that the command GPS – such as GPS 8 – is a macro command which configures many different aspects of the unit.  Most commonly the GPS command is understood by the user to set the format of the NMEA output, but it in fact does much more.  For instance, issuing  the command “GPS 8” to an Atlas PL will completely turn off the receiver circuitry of the unit. This is not what we need for a base station receiver or repeater.  The subsequent commands change other configurable attributes of the Atlas PL, overriding the macro set of configuration parameters, to arrive at the final desired configuration.  It is critical these configuration commands be issued after the GPS command.

We hope this demonstrates some of the capabilities of the Atlas PL not commonly identified by the end user.  Should you have in mind a specific function of an Atlas PL that is not apparent, we encourage you to contact us.

The ATLAS PL Personal GPS Locator operates off of two internal Lithium-Ion battery packs. Combined, the two batteries deliver 6.8 – 8.6V to the internal radio circuitry.  As the ATLAS PL is used, the batteries discharge, the battery voltage drops, and the RF power will slightly decrease.

Below is a table showing typical RF power output verses battery life.

The above data is represented graphically in the following chart:

The time duration that the ATLAS PL will operate before its batteries must be recharged is dependent upon the GPS mode and the position transmission/update rate.

Below is a chart showing approximate battery life.  The Green line is if the PL is operating in GPS mode 2, 4, or 9 with the UHF radio receive enabled.   The Blue line is GPS mode 9 with the receive disabled (Transmits position only).