RavTrack PC receives $PRAVE messages from a Raveon GPS tracking transponder, and uses the information in the $PRAVE message to plot the position and display the status of tracked vehicles and personnel.

The $PRAVE messages come out of the M7 GX transponder, when it is configured in GPS mode 2.  The serial port of the M7 GX transponder must be connected to the PC running RavTrack PC.   This connection may be a direct RS232 connection, or it may use a terminal server to convert the RS232 from the M7 GX transponder to Ethernet. The Ethernet connection is then made to a LAN or WAN so that RavTrack PC can receive the GPS positions via the nework connection.

To verify that RavTrack PC is receiving $PRAVE messages, you can look at the communications statistics window within RavTrack PC, and see if $PRAVE messages are comming out.

In the “Messages In” column, there are two numbers (xxx/yyy)  The first number xxx is the total number of messages, and the second number, yyy, is the total number of $PRAVE messages that RavTrack PC has received.

If the communications with the M7 GX transponder is OK, the second number will increment each time a $PRAVE message is received, which is each time a transponder reports in. In the above example, RavTrack PC has received 311 position reports using its network connection.

If the second number is 0, but the first number is not zero (ie  123/0)  then the connection to the M7 GX is probably OK, because some messages are coming in.  These are usually the $GPGGA/RMC type messages output from the local GPS in the M7.  They are not over-the-air position reports.  Because the first number is incrementing, the connection to the M7 is OK. But, because the second number is 0, there are not $PRAVE messages coming in.  The most likely reasons that there are not $PRAVE messages are:

1.  All transponders are turned off.

2.  The UHF or VHF antenna to the M7 GX used with RavTrack PC is not connected.

3. The encryption keyphrase is not set corectly, and the My GX cannot receive the position reports.

4. All transponders are out of range of the M7 GX used with RavTrack PC.

5. The transponders are configured on a different RF frequency.

Hopefully you find this information helpfull.  Monitoring the communication statistics is an excellent way to verify the performance of your RavTrack GPS tracking system.  RavTrac PC automatically monitors the statistics, and will turn the communication status button on the bottom of the screen red if no messages are received for a long period of time, indicating that the communications with the transponder used to receive $PRAVE messages has failed.

Microsoft SQL Server may be used as the database engine for the RavTrack PC AVL system.

A free version is available from Microsoft, called “Express”.  For small AVL systems where the number of tracked vehicles is small (< 25) and the update rate is fairly slow (< 30 seconds), then the EXPRESS version is probably a good choice. But, for systems requiring higher performance, Microsoft provides a number of high-performance options.

The following table describes the primary differences between the various SQL implementations.

Scalability and Performance

Feature	Express	Workgroup	Standard	Enterprise	Comments
Number of CPUs	1	2	4	Max OS supported	Includes support for multicore processors.
RAM Used	1 gig(GB)	3 GB	OS maximum	OS maximum	Memory limited by operating system.
64-bit Support	Windows on Windows (WOW)	WOW
Database Size	4 GB	No Limit	No Limit	No Limit
Partitioning					Support for large-scale databases
Parallel Index Operations					Parallel processing of indexing operations
Indexed Views					Indexed view creation is supported in all editions.

The RavTrack system offers very good coverage in many environments with a single base station and single antenna.  However, in some circumstances this is not sufficient to cover the entire tracked area, or other factors may move you to install multiple antenna locations.

First, before you decide that one receiving antenna is insufficient, take a look at your area.  Do you have a voice UHF system of about 5 watts?  The Ravtrack system coverage is typically similar to the voice system coverage, although not necessarily identical.

Consider if you can mounting the base station antenna as high as possible to cover the desired territory.  In some cases this may mean moving the antenna away from the control room to achieve the best coverage.  A skilled RF technician familiar with your area can probably determine a good antenna location, sometimes by performing a site survey, or simply by experience.

Because you want to keep the antenna cable that links the antenna to the receiving modem as short a possible, this may mean that the receiving modem is moved from the vicinity of the tracking PC.  RS232 serial communication links have strict distance limitations.  However, if you have (or can get) Ethernet/IP communications between the base modem and the computer you can use a “terminal server” (AKA telnet server, serial-IP convertor) to place the base modem onto the Ethernet/IP backbone.  From here the position updates are carried via network telnet services from the base modem to the PC.

This approach can also be used to spread mulitple receiving base stations around your area, to improve coverage.  Again, you need an Ethernet/IP backbone linking all the antenna sites to your tracking PC.  You may check with your I.T. department if you have one, for help.  The Ethernet/IP backbone may be wired or wireless.  A number of wireless solutions exist. 

If you use this approach make sure your tracking software can acquire the telnet stream (sometimes you may use another telnet server), and/or that it can acquire multiple base station modems.  RavTrack PC currently supports up to 6 base station modems.

For much more detail on using terminal servers see application note 140 “Using an Terminal Server to expand your Ccverage area” at the following link.

http://ravtrack.com/pdf_appnotes/AN140(RavTrackTermServ).pdf

If for whatever reason this approach is impractical, one or more repeaters may be in order.  Remember that with RavTrack you don’t need to order fancy equipment to provide the repeater.  Any RavTrack transponder can easily be programmed to serve as a store-and-forward repeater.  Just ensure you make good locati0n and antenna choices.  For more information on antennas see the following tech blog “Antennas for a RavTrack vehicle tracking system”:

http://ravtrack.com/GPStracking/2009/antennas-for-a-ravtrack-vehicle-tracking-system/

One of the  advantages of using a repeater in your system is that the repeater will “repeat” any vehicle transmission it receives back out over its entire area of coverage.  Remember your vehicle transponder not only sends its own position information, but can receive the same from other fleet members, a feature fairly unique to RavTrack.  So, if you are equipping vehicles with tracking displays to do just that, those vehicles will not only receive position reports from other nearby fleet members, but those that are further away as well when using a well positioned repeater. 

On the flipside, a store-and-forward repeater does just that, it first receives and stores a transmission, then repeats out that same transmission.  While the RavTrack transponder has an extremely quick turn-around time from receiving to transmitting, it still will take time to receive then repeat.  Because of this the total duration of a transmission may need to be extended by lengthening the duration of each transmission slot in the system, and  you may want to recalculate system timing parameters and overall system performance and scalability projections.  If you have multiple repeaters they may require  further time slot expansions.  This is the prevalent case if you deploy each repeater using the same repeat frequency.  For more information on system timing with and without repeaters please refer to the techblog  “TDMA Time Slots”: 

http://ravtrack.com/GPStracking/2009/tdma-time-slots/

If your scenario will require you to install multiple repeaters, there are different methods for doing this as well, and different tradeoffs in the process. 

Whatever issues you face we encourage you to contact us so we can help you work towards the best approach for your particular 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.

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 style magnetic mount

Antenna threading onto NMO flange  mount.

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:

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:

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:

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

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:

  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:

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:

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.