The M7 transceiver has a 5-watt RF power output rating.  In a typical application the units is in Standby or Receive mode most of the time.  A small fraction of the time, it is transmitting.  But when it transmits, the M7 begins heating up, dissapating about 8 watts of heat.   This depends upon the RF power output setting and the DC input voltage. 

The temperature of the M7 enclusure must be kept below 60 degrees celcius, (140 farenheit) for proper operation of the unit.  For GPS transponder operation, there is no problem doing this, because the duty cycle is low.  But, if the M7 is used to send data, and is on the air a lare percentage of the time, then the enclusure’s temperature will begin to rise.  The following chart shows the case temperature at 25% and 50% Duty cycle. 

 

M7 Duty Cycle

You can see in the chart, that the M7’s enclosure temperature gets hotter if the DC input voltage is higher, or if the duty cycle is higher.  

For example, if the DC input voltage is 10V, and the unit is operated at 25% transmit duty cycle, then the enclosure temperature would be about 42 degrees C.  Given the same duty cycle, the enclosure temperature would be 46 degrees if the DC input were to be 14 volts. 

Raveon offers a heatsink option for the M7.  The heatsink is large finned heatsink that covers the top of the M7, and is secured on with thermally-conductive epoxy.  When this heatsink is attached, the M7 will stay cooler.  The following chart illustrates this:

The above data is the M7’s enslosure temperature with a heatsink secured to it.  The heatsink covers the top of the enclosure and uses normal air convection (no fan).  It reduces the case temperature by about 4-8 degrees.  

If a CPU cooling fan or similar fan were added instead, the case temperature rise would be only a few degrees above ambient.

The M7 GX series of GPS transponders may be directly connected to a Lowrance Globalmap 540C or a Globalmap 840C navigation display. When connected, the Lowrance display map will show the location of the vehicle it is in PLUS the location of all other M7 transponders within radio range.  This unique feature allows one to quickly, easily, and inexpensively, make a mobile AVL system for tracking cars, trucks, racecars, construction equipment, or any thing Raveon’s M7 GX transponder may be installed on.

Both the 540C and 840C have built-in interfaces for a “NMEA 0183″ devices, which is another way of saying that they can connect to other devices using a serial cable.   The NMEA 0183 is an RS232 serial connection that typically operates at 4800 baud.  It is used to exchange waypoint and other information between displays, GPS devices, and transponders.

When Raveon’s M7 GX transponder is connected to the Lowarnce diplay using the NMEA 0183 connection, the M7 transponder can put icons on the screen of the Lowrance display.  As the transponder received updated positions from other vehicles, it updates the position of the icons on the Lowrance display.

Lowrance 540C and 840C Wiring

From the Lowranace technical manual, here is how their NMEA 0183 interface works:

NMEA 0183 Cable Connections

NMEA 0183 is a standard communications format for marine electronic equipment. For example, an autopilot can connect to the NMEA interface on the GlobalMap 540c and receive positioning information.  The GlobalMap 540c can exchange information with any device that transmits or receives NMEA 0183 data. See the following diagram for general wiring connections. Read yourother product’s owner’s manual for more wiring information.

NMEA 0183 Wiring  (Data cable)

To exchange NMEA 0183 data, the GlobalMap 540c has one NMEA 0183 version 2.0 communication port. Com port one (Com-1) can be used to receive NMEA format GPS data. The com port can also transmit NMEA format GPS data to another device.  The four wires for the com port are combined with the Power Supply cable and NMEA 2000 Power cable to form the power/data cable (shown earlier). Com-1 uses the yellow wire to transmit, the orange wire to receive and the shield wire for signal ground. Your unit does not use the blue wire.

 Wiring the DB9

The Lowrance’s “Data Cable” must be connected to the M7 transponder.  This connection will allow the M7 to put icons on the screen of the Lowrance display, showing the location of other tracked vehicles.  The Raveon M7 GPS transponder uses a 9-pin “DB9″ connector to connect to the Lowrance.  Solder the Lowrance data cable wires onto a DB9 connector and plug the DB9 into the M7 transponder as shown below:

The orange wire goes to pin two of the DB9, the yellow wire to pin 3, and the shield braid of he cable connects to pin 5 of the DB9.  The blue wire is trimmed off.

The extra wires on the Lowrance display called NMEA 2000 power are typically not used in a vehicle installation, and may be wrapped up with electrical tape and tucked away.  

Configuring the Lowrance

Set the NMEA communication of the Lowrance to 4800 baud.

Configuring the M7 GX Transponder

Raveon has a designed the M7 GX transponder to work with Lowrance Display or any other NMEA 0183 display that can accept the “$GPWPL” NMEA message.   The $GPWPL is an industry standard message that the Lowrance displays and many other GPS displays interpret as a waypoint command.  The M7 GX outputs this $GPWPL message to put icons on the screen of the Lowarance, and to move the icons around on its screen.

To configure the M7 transponder to output the $GPWPL message, set the M7 GX to GPS mode 2.  To do this, put it into the configuration mode by send the +++ into the serial port.  The M7 will respond with an OK.  Type GPS 4 and press enter to put it into GPS 4 mode.  GPS 4 is the mode that causes the M7 GX to output $GPWPL messages whenever it receives a status/position message over the air.

Internal to Raveon’s M7 series of GPS transponders is a GPS receiver module made by Trimble.  It is their Copernicus II GPS receiver module.  Many of the M7’s performance specifications are driven by the use of this receiver module.  The Copernicus II is ideally suited for vehicle tracking systems, AVL, asset tracking, and personal location.   Details of the module are available on Trimble’s website at: http://www.trimble.com/embeddedsystems/copernicus.aspx?dtID=overview 

The following is a summery of the Copernicus GPS modules features and performance:

Overview

Trimble’s Copernicus® GPS receiver delivers proven performance and Trimble quality for a new generation of position-enabled products. It features the Trimble revolutionary TrimCore™ software technology for extremely fast startup times and high performance in foliage canopy and urban canyon environments. The Copernicus module is a complete 12-channel SBAS (which includes WAAS, EGNOS) capable GPS receiver in a thumbnail-sized module. Each module is manufactured and factory tested to Trimble’s highest quality standards.

Key Features:

• 2.54 mm T x 19 mm W x 19 mm L
• 94 mW typical continuous tracking
• Supports SBAS (WAAS, EGNOS)
• Active or passive antennas
• NMEA, TSIP, TAIP protocols
• RoHS-Compliant (Pb-free)

The sensitive Copernicus II GPS receiver can autonomously acquire GPS satellite signals and quickly generate reliable position fixes in extremely challenging environments and under poor signal conditions The unit also accepts aided GPS (A-GPS) data for faster startups in very weak conditions.  The Copernicus II GPS module is a complete drop-in, ready-to-go receiver that provides position, velocity, and time data in a user’s choice of three protocols Trimble’s powerful TSIP protocol offers complete control over receiver operation and provides detailed satellite information.

PERFORMANCE SPECIFICATIONS

Accuracy (24 hr static)

• Horizontal. <2.5 m 50%, <5 m 90%
• SBAS. <2.0 m 50%, <4 m 90%
• Altitude. <5 m 50%, <8 m 90%
• SBAS. <3 m 50%, <5 m 90%
• Velocity. 0.06 m/sec
• Static PPs. +/- 60ns RMS
• PPS (Stationary Mode “indoor” @ -145dBm). +/-350ns

Acquisition (Autonomous, -130dBm, 50%)

• Reacquisition. 2 s
• Hot Start. 3 s
• Hot Start without battery backup. 8 s*
• Warm Start. 35 s
• Cold Start. 38 s

Sensitivity (unaided)

• Tracking . -160 dBm
• Acquisition. -146 dBm
• Receiver Dynamics. 2G

Raveon’s M7 GX AVL transceiver uses a  Time Division Multiple Access (TDMA) protocol to transmit position, status, and data over the air.  TDMA protocols greatly increase the available channel bandwidth but they require more system planning than conventional carrier-sense methods. 

With a TDMA system, each radio in the system is assigned a time slot to use for sending its data (data being GPS postion, status, or ASCII data).   Because only one radio transmits in any single timeslot, there is never any interference between radios.  Hundreds of GPS tracked vehicles or assets may be all located in the same place, and still communicate without interference – an impossible task with conventional radio systems.

The M7 radio’s TDMA timing may be configured by the system installer to optimize it for a particular application.  The TDMA slot width and the number of slots maybe configured to achieve the maximum system performance.  Each TDMA slot needs to be long enough so that the complete GPS position/status message can be sent in it. 

 Table 1 below shows the recommended slot times for various over-the-air data rates. 

Use the ATR2 x command to set the over the air rate.  Use the SLOTTIME xx to set the TDMA slot time.  The SLOTTIME must be wide enough to accommodate a Position/Status transmission from the GPS.  Refer to the Table 1 above to determine how long a position/status transmission will take.  The factory default for a stock RV-M7-UC-GX radio is 200mS slots, 4800 baud over-the-air.  This is an excellent compromise between speed and communication range. 

The TDMA Frame Length

 The TDMATIME is the length of one TDMA frame/epoch.  A TDMA frame contains small time slots where each radio is allowed to transmit in.  The slots are sequentially numbered.  For example, in the configuration below, the TDMA frame is configured to have 20 slots.

Figure 1

Radio number 1 transmits in Slot 1. Radio number 2 in slot 2… 

TDMA Frames have a pre-set number of slots, and once the TDMA Frame Time has passed, the frame restarts at slot 0 again.  Slot 0 is reserved for future base-station control signals.  The length of a TDMA Frame is set with the TDMATIME xx command. 

 Figure 2

In the M7 GX radio, the TDMA Slot Time is programmable, in 50mS increments.  The SLOTTIME xx command is used to set the slot width.  Typically it is set at 50, 100, 150, or 200mS.  The factory default is 200mS. 

For example, with a TDMATIME of 4 second, and a SLOTTIME of 200mS, there are enough slots to support 19 radios reporting every 4 seconds.  The Frame will repeat every second so every second, each of the 19 radios has 200mS of air-time available.   Figure 3 depicts this configuration.

 Figure 3

Configuration 1 below shows the slot timing with a 1200 baud M7 GX radio using 750mS time slots. 

 Configuration 1

Configuration 2 below shows the slot timing with a 4800 baud M7 GX radio using 200mS time slots. 

 Configuration 2

Creating and Finding Map Images

All GPS Tracking software programs need some source of image files to overlay the position of the things being tracked.  The Internet provides a rich source of map images, and this page identifies some of the better sources.  If you find others, please let us know about them. 

RavTrack PC GPS Tracking Software by Raveon uses uses map files stored in the “.maplib” format.  This format was developed by Franson for display geo-referenced map images.   Virtually any type of image may be converted to a “.maplib” file, using the built-in calibration tool within RavTrack PC.   Images or maps that are in the  .jpg, .tiff, .bmp, and .gif file format may be converted.  Aditionally, any file in the “.geotiff” file format may be inported as a .maplib file, and the calibration in the .geotiff file will be used.

Below are some links to websites that provide map imagery for GPS tracking use. 

Topographic Maps in .geotiff format

  Low-cost topo  maps, pre-calibrated in .geotiff format.  
  http://www.ChartTiff.com/wwwref_RavTrack.htm

Map Image Service

Digital Data Services Inc. provides custom map service.  Contact them if you would like them to create a custom map image for your location.  Remember to ask for the file in .geotiff format, so that you do not have to calibrate it when using it with RavTrack PC. 

  http://www.usgsquads.com/svcs_custom_maps.htm