Multiple Base Antennas vs Repeaters in a RavTrack System

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.