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Battery Comparison for GPS Tracking Device

Overview

Many different types of batteries may be used with Raveon’s M7 series of GPS transponders.  This Technical Brief describes how well some common battery types will work with the M7 radios. 

Actual battery life will vary based upon how often the M7 GPS transponder transmits, but the data in this Technical Brief may be used to predict the battery life of most configurations.

Test Setup

For the tests in this brief, a UHF GPS transponder, model RV-M7-UC-GX was configured in GPS mode 2 to transmit its position every 10 seconds.  In GPS mode 2, the radio’s receiver is on 100% of the time, and the current draw of the M7 was an average of 90mA.  The peak current draw was 2.1 amps for 68mS each time the M7 transmitted its GPS position.

Summary Data

Brand Type Recharge-able mAh Life
(RX on)
Life
(RX off)
Duracell Alkaline NO 1600 18 hours 36
Energizer Lithium NO 2500 28 hours 56
Lenmar NiMH Yes 1500 17 hours 34

Duracell Alkaline

These batteries are the common Duracel batteries found at most department stores.

Test Result Summary

Initial Voltage:                                   12.57 volts

Voltage at ½ discharge:                   10.2 volts

Usable life (hours)                           18 hours

Voltage drop when transmitting       2.4V  (1.1 ohm resistance)

Approximate mAh capacity             1600mAh

Discharge Curve

Transmit Transient

The plot below shows the dip in voltage as the transmitter turns on and off.


Summary

The Duracell is an OK battery to power the M7 transponder.  But its high internal resistance will reduce the RF power output after the first few hours of operation.  The DC to the radio should stay above 9V while transmitting for full power, above 8V for 3-4 watts.


Energizer Lithium

These batteries are the common Energizer Lithium batteries for cameras and digital electronics found at many department stores.

Test Result Summary

Initial Voltage:                                      12.1 volts  (14V for a few moments)

Voltage at ½ discharge:                      12.0 volts

Usable life (hours)                              28 hours

Voltage drop when transmitting          3.5V  (1.6 ohm resistance)

Approximate mAh capacity                2520mAh

Discharge Curve

Transmit Transient

The plot below shows the dip in voltage as the transmitter turns on and off.

Summary

Even though the internal resistance of the cell is higher than the alkaline, the Energizer Lithium is a good battery to power the M7 transponder.  Its high internal resistance will not reduce the RF power output because its voltage is fundamentally fairly high.  The DC to the radio should stay above 9V while transmitting for full power, above 8V for 3-4 watts, so the 3.5V dip means the radio will have full power at 12.5V, and 3-4 watts out at 11V DC at the battery pack.


Lenmar R2G NiMH pack, 2150mAh cells

These batteries are Nickel Metal Hydride rechargeable batteries.  They were fully charged before the test.

Test Result Summary

Initial Voltage:                                      11.0 volts

Voltage at ½ discharge:                      10.3volts

Usable life (hours)                              17 hours

Voltage drop when transmitting          2.0V  (.95 ohm resistance)

Approximate mAh capacity                1500mAh

Discharge Curve

Summary

These batteries should be a good power source for the M7 GX transponder.

The internal cell resistance is low, but the voltage is also low. The RF power output stayed at full power for most of the life of the battery, dropping to about 4 watts at the end of the battery life.  The double dip at end of live was due to the fact the radio keep working down to 6 volts (albeit with almost no RF output because the RF PA is off), and the batteries keep putting our very low voltage for another couple hours.

This article describes batteries that may be used for an AVL system, but Raveon’s UHF Radio Modems may also be battery powered, so this article can be applied to these radios also.

Raveon Technologies Corporation

990 Park Center Drive, C

Vista, CA 92081

sales@raveontech.com

760-727-8004

TDMA Transmission Overview

TDMA, or Time-Division-Multiple-Access is a very effective way of allowing a lot of radios to share one radio channel.  Used extensively in GSM cellular and APCO public-safety systems, TDMA excels at allowing quick and reliable access to radio channels.  Raveon’s M7 series of GPS tracking radios use TDMA to send GPS position information, status, and data. It allows 2-10 times more radios to share a radio channel than conventional carrier-sense methods.  This allows 2-10 times more tracking radios on one channel, as compared to radios that do not have TDMA capability.

The following diagram illustrates how it works.

When a RV-M7 GX wants to report its position and status, it waits until its assigned time-slot, and then transmits its data.  By default, TDMA time slot positions are assigned by unit-ID, so RV-M7 GX with ID 1 uses the first slot, and ID 2 uses the second slot, and so on.

A TDMA “Frame” time is the time it takes all units to transmit once.  This is configured with the TDMATIME xx command.  The factory default is 10 seconds, so every 10 seconds, each RV-M7 GX may transmit.  The TDMA frame must be set long enough for all units to transmit.  For example, if you have 50 RV-M7s, and use 200mS TDMA slots, then the TDMATIME should be set to 10 seconds.  The simplest way to set it the TDMATIME is to make it equal to the TXRATE, the rate you wish to report position

The duration of a TDMA time slot is programmed into the RV-M7 GX with the SLOTTIME command. If SLOTTIME is set to 200 milliseconds (factory default), then every 10 seconds, the RV-M7 will have a 200mS window to report its position in.

All TDMA frames are synchronized automatically in all RV-M7 GX Transponders to the top of the minute.  Slot 0, frame 0 is at the top of each minute. They use the internal GPS receiver to determine the current time, and calculate when their are supposed to transmit their position and status information.

A unit may be allocated additional time slots.  The SLOTQTY command sets the number of slots each unit receives.  It is normally set to 1.

Criterion International

After searching for and testing several UHF radios to upgrade a municipal water department’s wireless SCADA system, RAVEON’s Fireline modem was chosen as the best performance/value solution. The simple and versatile ability of the Fireline to be quickly configured easily beat out the other radios on the market. Thirty + radios have been installed and in service continuously operating with no problems for over two years.

Regards.

Chris Carda

President

Criterion Industrial

Identifying Digital Input States in a $PRAVE message

The $PRAVE message has the status of each input as represented by a single digit hexadecimal number in field 12. For example, the the $PRAVE message below, the last 3 represents the digital inputs from transponder 0001.

$PRAVE,0001,0001,3308.9051,-11713.1164,195348,1,10,168,31,13.3,3,-83,0,0,,*66

In this example field 12 has value 3.  The field 12 value is the hexadecimal binary representation of the bits.  Refer to the following table:

IN 2
(TXD)

IN 1
(RTS)

IN 0
(DTR)

Hexadecimal Representation

0

0

0

0

0

0

1

1

0

1

0

2

0

1

1

3

1

0

0

4

1

0

1

5

1

1

0

6

1

1

1

7

The stock RV-M7 GX has up to 3 digital inputs, using the input pins of the RS-232 serial port.  An open circuit or ground is a 0, and if they are connected to a positive voltage greater than 3V, they are a digital 1. If all 3 pins are allowed to float (nothing connected – same as ground) the value should be 0.  If positive voltage is applied to a pin the pin value will be 1.  The field 12 value will be 1 or 2 or 4, depending on which pin had the voltage applied.

RS-232 Pin

Function

4 – DTR

Input 0

7 – RTS

Input 1

3 – TXD

Input 2

5 – Ground

GND

Connect to vehicle chassis or other ground point.

Note that the weatherproofed (-WX) model has less RS-232 pins and only 2 digital inputs.  Inputs 1 and 2 are valid, but input 0 is indeterminate (state can float).

In the RavTrack PC software it is easy to not monitor this missing pin, so any change of state or change of value of this pin would not matter to the software.  Simply configure this input as unused.

1aa

RS-232 Pin

Function

4 – RTS

Input 1

3 – TXD

Input 2

5 – Ground

GND

Connect to vehicle chassis or other ground point.

On the M7 series of transponders, if an input is left floating/unconnected, the transponder will read it as a digital 0 (low), and report it this way.

Dual Bandwidth Capable. Wide and narrow-band explained.

Raveon Technologies data radio modems can have either wide band IF filters, which are used on 25kHz or 30kHz spaced channels, or narrow-band IF filters, which are used on 12.5kHz spaced channels.

 

As the picture above illustrates, it is possible to have twice the number of radio channels, when everyone uses 12.5kHz narrow band radios.

So, why is this important?  There are two big reasons:

1. Your radio system must have receivers with the proper IF bandwidths to perform properly and meet regulatory specifications.

2. In the USA, the government has mandated that all all Part 90 Business, Educational, Industrial, Public Safety, and State and Local Government VHF (150-174 MHz) and UHF (421-512 MHz) private PLMR (Private Land Mobile Radio) system licensees convert to narrow-band operation by 2013.

Raveon Technologies is here to help you migrate your system to narrow-band technology.  Our M7 series of radios supports both wide and narrow-band operation, and our new VHF M7 supports both in the same radio.

  Wide Band Narrow Band
Channel Spacing 25kHz or 30kHz 12.5kHz
Actual receiver IF filter bandwidth 15kHz 7.5kHz
Maximum data rate with  standard modulation 9600 baud 4800 baud
Maximum data rate with  4-level modulation 19200 baud 9600 baud

Because the IF bandwidth in a narrow-band radio must be 1/2 the bandwidth of a wide-band radio, the over-the-air data rate will be 1/2 also.   And unlike other brand radio modems that loose sensitivity when operating on narrow channels, the M7 series of radios has the same high receiver sensitivity on both wide and narrow-band channels.

Raveon’s UHF data radio modem, the RV-M7-U, may be ordered as either a wide-band or a narrow-band radio.  It is configured at the factory for one or the other.

Raveon’s new VHF data radio modem, the RV-M7-V, is dual-bandwidth capable and user-configurable for either  wide-band or narrow-band .  It has 6-channel memories in it, and each channel may be set to either wide or narrow band.

A narrow-band radio can usually communicate with a wide-band radio, if they are set to the same over-the-air data rate as the narrow-band radio.  But because the wide-band radio has overly-wide IF filters for the signal, the communication range will not be as good as two narrow-band or two wide-band radios communicating.

A wide-band radio will not communicate with a narrow-band radio.  In the voice world it might work, but in the data world, the narrow IF filter in a narrow-band radio will filter off the wide-band signal, and no reliable communications will be possible.

So, if you are migrating your wire data system, SCADA system, or telemetry system from wide to narrow-band, you must make sure all radios in the system have the same IF bandwidths and over-the-air data rates.  Please contact Raveon Technologies for either wide-band or narrow-band data radio modems.

Links to FCC Documents regarding the narrow-band migration:

< http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-04-292A1.doc>

< http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-04-292A1.pdf>

< http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-04-292A1.txt>

GPS Position Accuracy

The accuracy of a position determined by using a GPS receiver is limited by the accuracy of the GPS signal itself.  The US government controls the precision of the GPS signals sent from the GPS satellite constellation.   It varies from day to day, and the following graph shows historically, how precise the GPS position information is.

gpsaccuracyRaveon’s GPS transponders utilize the WAAS signal, so accuracies of 2-3 meters are possible.  Laboratory tests with the M7 series of GPS transponders confirm that this is possible, but typically, the accuracy is in the 3-5 meter range.

If the GPS transponder is located indoors, or if there are very tall buildings near the transponder, the accuracy will be degraded due to multipath of the GPS signal.

Antennas for a RavTrack vehicle tracking system

In a RavTrack system you will need antennas for vehicles, as well as base stations, and possibly repeaters if your particular system uses any repeaters.   Here will will discuss common antennas for all three uses.

The Raveon “GX” series of tracking transponders used in a RavTrack system can be configured to operate as a vehicle unit, a base station, or a repeater, all by software configuration.  Each GX transponder will have 2 antenna connections.  One is for a GPS antenna, and the other for a UHF antenna.

Here is a picture of the GX transponder in the standard enclosure.  Note that the GPS antenna connector is an SMA female, while the UHF connector is a BNC female.  They are at opposite ends of the transponder.

 

transponder-and-antenna-connectors 

Note that if your transponder is the weatherproof version  the UHF connector is TNC female.  Transponders installed in vehicles for tracking purposes will require both a GPS antenna and a UHF antenna. We have a few antennas that are combination GPS and UHF antennas.  When these are offered the antenna cable(s) will terminate in 2 separate connections. 

The GPS antenna receives the GPS satellite transmissions by which the transponder will determine its precise GPS location.  Note that the location is actually that of the antenna itself, which may be important to remember especially when dealing with large vehicles or other objects.

Once the location is determined the UHF antenna is required to allow transmission of the vehicle location.  The UHF antenna should be a “mobile” antenna chosen to match the proper transmission frequency of your system, as well as selected to best suit the type of vehicle.  The UHF antenna is almost always larger than the GPS antenna so size and styling can be important criteria.

Anther important criterion is the manner in which the antennas mount to the vehicle.    It is best to have the antennas as high up on the vehicles as practical, and generally speaking larger (UHF) antennas are typically better performers.  However an overly large antenna may not just be unsightly but prone to damage as well.  Some vehicles will be equipped with an “antenna bar” in order to mount the antennas.  As multiple antennas may posssibly compete with one another, it is best if a skilled RF technician is consulted or contracted to perform the installation.

Antenna mounts come in a variety of approaches of which the 3 most common are magnetic mount, through-hole mount, and flange mount.  The magnetic mount is most suitable for temporary installations, although the magnets are quite strong and the antennas may stay put even under challenging circumstances.  The through-hole mount is the sturdiest and most permanent, but requires a hole be drilled through the vehicle surface (or antenna bar).  The flange mount approach is typically used to grip the vehicle trunk lid, if this is available.  All of these mounts are available in “NMO” style where the UHF antenna physically threads on to the mount itself.  Here are some quick photos:

 

nmo-mag-mount5

NMO style magnetic mount

 

nmo-antenna-combines-to-mount6

 

 

 

 

 

 

 

 

 

 

 

 

 

Antenna threading onto NMO flange  mount.

 

thru-hole-nmo-mount4

 

 

 

 

Thorough-hole mount.

 

For more information on NMO mounts see the post “The versatile NMO antenna mount” in this section at:

http://ravtrack.com/GPStracking/2009/the-versatile-nmo-antenna-mount/

Oftten the GPS and/or UHF antenna will have a magnetic mount base or through-hole mount base incorporated as the antenna base.  Here is a photo of a combo GPS/UHF antenna with a through-hole base:

 

 

combo-antenna-thruhole

 

 

 

 

 

 

 

 

In some vehicle deployments the UHF antenna will not only broadcast location but will also receive transponder broadcasts from other fleet members.  This ability is fairly unigue to Ravtrack.

Once a location broadcast hits the air it is ready to be received by other fleet members but also by a base station or possibly a repeater.  Sometimes the base station is mounted on a mobile command vehicle, and special antenna considerations are in order.   However, typically the base station antenna is on top of a building, or an antenna tower.  Usually an omni-directional (all direction) antenna is used, as the vehicles can be broadcasting from many different locations. 

The most common omni-directional base station antenna is made with a fiberglass sheath.  Here is a picture:

 

fiberglass-antenna

 

 

 

 

 

 

 

 

 

This sort of antenna typically mounts onto a pole or mast the customer provides.  Check to see if the actual mounting hardware is included with the antenna. 

This antenna is also very effective for repeaters.  Sometimes, if a repeater is used the base station will use a directional antenna pointed at the repeater antenna.  Here is a picture of a Yagi style directional antenna used for this purpose:

 

yagi

 

 

 

 

Antennas can act as lightning attractors, so you may want to investigate lightning arrestors for some installations.

Here are some general rules if thumb when dealing with antenna installations::

 

Survey your area for best antenna locations

  

 

 

 

Use the largest antenna you can tolerate and afford

 

Make certain the antenna will work in your frequency

 

Determine your mounting and support early

 

Mount the antenna as high as practical

 

Try to keep the antenna cable short, and use good grade cabling

 

Take precautions against lightning and surge

 

Don’t forget signal cable and power for your transponders

 

Hire a skilled RF technician if at all possible

 

 

The versatile NMO antenna mount

A popular type of antenna mount is called an “NMO” which stand for new Motorola.  NMO mounts come in a variety of types and are frequently used especially when installing mobile antennas.  Whether you are installing an antenna on a vehicle or a fixed structure the NMO mount may be a good solution.

The idea of the NMO mount is simple.  NMO mounts are devised to have a standard threaded connector where you screw on the antenna of choice to the mount of choice.  The NMO mount itself connects to the antenna and provides the antenna cable as well.  There are a large number of antennas that are built to screw on to the NMO mount. Simply look for an antenna with an NMO base.  Here is a simple picture of a mobile antenna with an NMO base combining to an NMO mount:

 

nmo-antenna-combines-to-mount

 

  Here an antenna with an NMO base will thread on to the NMO mount.  Note the antenna cable comes from the mount itself.

The NMO mount in the above example is a “trunk lid” mount.  The flange to the left hooks under the lid of a vehicle trunk.

Another popular type of NMO mount is the magnetic mount.  When affixed to many metallic surfaces the mount stays put quite well.  Here is a picture:

 

nmo-mag-mount

 

A third popular type  of mount is the through-hole mount.  This  requires a small (typically 3/8″ to 3/4″ ) hole be drilled through the surface hosting the mount, and is the best choice for an extremely rugged installation.  The “NMO” part of the mount protrudes above the mounting surface, becoming accessible to the antenna itself.  Here is a picture of a through-hole NMO mount:

 

thru-hole-nmo-mount

The following external post provides a good look at a through-hole NMO mount assembly and brief description of the approach

http://www.radioreference.com/forums/radio-equipment-installation-forum/97536-install-nmo-antenna.html

 

The installation of a through-hole NMO mount and antenna is covered by this external video.  The video was shot by a fellow holding the camera in one hand while trying to perform the installation, so it is a bit shaky, but all-in-all he does an excellent job:

http://www.youtube.com/watch?v=zs-0EF7mP8k

 

Raveon can provide several NMO mounts and antenna types.  We invite your further questions.

 

 

 

 

 

M7 Heat Sinking and Duty Cycle

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, dissipating about 8 watts of heat.   This depends upon the RF power output setting and the DC input voltage.

As a precaution to protect the M7 radio modem from over-heating, the M7 has thermal protection built into it.  When the internal circuits exceed 70 degrees Celsius, it will automatically turn its output power down by about 3dB.  If the transmissions continue and the heating continues, at around 75-80 degrees Celsius, the RF power amplifier will shut down to protect it and other circuits.  It only will remain shut down till the next transmission attempt, and at that time, if it has cooled off below 70C, it will begin transmitting again. 

The temperature of the M7 enclosure must be kept below 60 degrees Celsius, (140 Fahrenheit) 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 large percentage of the time, then the enclosure’s temperature will begin to rise.  The following chart shows the case temperature at 25% and 50% Duty cycle.

M7 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:

m7dutycycle-heatsink

The above data is the M7’s enclosure 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.

For technical information about Raveon’s UHF data radio modems, <click here>

For technical information about Raveon’s VHF data radio modems, <click here>

The M7 data radio transceiver with the optional heatsink attached is shown below.

Connecting the M7 to a Lowrance display

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.540cwiring-to-m7

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:db9-lowrance-31

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.