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.

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

The M7’s I/O Connector

On the front of the M7 series of transponders, is an Input / output (I/O) connector used to configure the unit.  This I/O connector supports RS232 serial data (422 optionally), as well as digital input and output.  

The RS232 9-pin serial I/O connector is a female 9-pin D-subminiature connector having the following pins configuration.  It is pinned out so that it may be plugged directly into a computer or PC’s 9-pin COM port. 

DB9 Female I/O connector

Front-view of DB-9 connector on modem (female)

Note:   RS-232 signals use positive and negative voltages to represent digital 1s and 0s.  A positive voltage is a 0, and a negative voltage is a digital 1.

This I/O pin-out allows the M7 to be directly plugged into a PC computer’s 9-pin serial port using a conventional 9-pin RS-232 serial cable.  To connect it to a modem, or peripheral that has a serial port, you will need a “null-modem” cable.  

Null Modem Cables

Sometimes, a “Null Modem” cable may be required to connect the M7 modem to another device.  The specific connections are very dependent upon the type of hardware and handshaking used, but the following sections should help in configuring a null-modem cable.

How to use the handshaking lines in a null modem configuration? The simplest way is to don’t use them at all. In that situation, only the data lines and signal ground are cross connected in the null modem communication cable. All other pins have no connection. An example of such a null modem cable without handshaking can be seen in the figure below.

Simple Null-Modem Wiring Diagram

 (Same wiring for male-to-male or female-to-femal cable)

If you are connecting your M7 to a Lowrance or Garmin GPS display, then you will need a null-modem cable to connect the M7 to the display. Lowrance provides a serial cable for its GPSs with “pigtail” wires, so you can solder your own DB9 male connector to it, and plug the Lowrance directly into the M7.

To connect a Garmin GPS, use a null-modem cable to connect it to the M7, or the supplied Garmin serial cable and a “Null Modem Adaptor”.

Digital Inputs

The M7 GX Transponder has 3 digital inputs, called Trigger Bits.  Trigger Bits are digital inputs that trigger the M7 GX to report its position and status.  Normally these inputs are used for RS-232 signals, but they may be used for general-purpose digital inputs.  The M7 GX may be configured to trigger a position/status report based upon the digital input bits state.

Important: If the digital input function is not needed, the TRIGBITS setting must be set to 0.  This is the factory-default setting, and unexpected transmission may happen if the digital inputs are enabled and not used.

If you are not using digital inputs to initiate a transmission, the TRIGBITS must be set to 0. (TRIGBITS 0 command)

If the RV-M7 GX was configured to transmit less-often when it is not moving, activation of the digital inputs will override this causing the unit to report at the interval programmed with the TXRATE command.  The digital inputs may be configured to be active high, active low, or active on a change in state.  The following table lists the available digital inputs on the standard RV-M7 GX:

 There are 3 commands that must be configured to use the digital inputs:

TRIGBITS x        This command enables or disables individual bits for use as input triggers.

TRIGPOL x         Sets the polarity of the input.  0=active high, 1=inverted, active low.

TRIGEX x            Sets which bits are used to report on exception. Exception reporting is when a position/status report is generated when an input changes either low-to-high or high-to-low.

The xx parameter is the hex binary representation of the bits.  Refer to the following table to see the value for x.

 For example, to enable bits 0 and 2 (DTR and TxD pins) to be used as digital input, issue the following commend:

TRIGBITS 5

If the bits are to be normally active high, then the polarity must be set to 0 (TRIGPOL 0 command).  To set bit 0 so that it is inverted (active low), use the following command:

TRIGPOL 1

This will cause the unit to transmit when bit 0 (DTR pin) is low.

To enable exception reporting, that is transmit when a pin changes from low-to-high or high-to-low, use the TRIGEX command.  When TRIGEX is 0, all inputs are active either high or low.  When a bit is set to 1 in TRIGEX, then that bit will cause the unit to transmit position/status anytime it changes state.

For example, to configure the unit to transmit position when bit 0 changes state, issue these commands:

TRIGBITS 1  (enables bit 0)

TRIGEX 1 (configures bit 0 for exception reporting)

To configure all bits to be used to report when they change, issue these commands:

TRIGBITS 7 (enables bit 0, 1 and 2)

TRIGEX 7 (configures bit 0, 1, and 2 for exception reporting)

To configure bit 0 to be used to report when it changes, bit 1 to cause a report when it goes low, and disable bit 2, use these commands.

TRIGBITS 3 (enables bit 0 and 1, disable 2)

TRIGEX 1 (configures bit 0 for exception reporting)

TRIGPOL 2 (configures bit 1 for active-low reporting)