Read The Last Recption’s Signal Strength

The command ATRSreturns the signal strength (in dBm) of the last message that the radio modem you issue it to received. 

The wireless data radio modem must be in the “Command Mode”.  To put the radio modem into the Command Mode, connect to the radio modem using a terminal program such as HyperTerminal or TeraTerm.   If the data radio modem has Ethernet capability, log into it as administrator.  Issue the +++ sequence.  this is three plus signs, with nothing before or after them.  The radio modem will respond with its model number and an OK: prompt when it enters the command mode. 

When you are in the command mode, type ATRS followed by the Enter key.  The  radio will return the signal strength of the last packet it received, followed by an OK prompt as shown below:

OK
ATRS
-92
OK

This indicates the last packet of data that the radio received over-the-air had a signal strength of -92dBm. 

Read the Reception History

There is a short history buffer in the radio that keeps track of the signal strengh and time of the last few packets.  The ATHS command will display a table of the historical packet signal strength and times. 

OK aths ROM RSSI TIME 0000 0 0 0000 0 0 0000 0 0 0000 0 0 1000 -110 33 0002 -75 45 08EA -99 122 0002 -74 131 OK

The most recent reception is on the bottom of the list.

Ping Another Data Radio Modem

The above two processes rely upon having received something from another radio.  There are cases when a newly installed radio has not yet received any data over the air.    In these cases it may be better to ping a remote radio.  You can send a “PING” message out one data radio modem to another.  A PING will cause the remote radio to respond with a short PING BACK message that the originating radio modem will receive.  Embedded in the PING BACK message is the received signal strength that the remote radio modem received the PING message at. 

When the originating radio modem receives the PING BACKmessage from the remote radio, it outputs the ID of the remote radio, and the Received Signal Strength (RSSI) that the remote radio read when it received the PING message.

Note, for PING to work the “Remote Access” must be enable on the remote radio.  By default it is enabled.  The command ATRV 0 enables remote access and ATRV 1 disables it.

Shown below is an example of how a PING command will look, when a radio modem pings unit 0002.

ok ping 0002 <RPR> FROM=0002 -74</RPR> ok

Read the Instantaneous Signal Strength

There is a command within the Raveon data radio modem that allows you to read the current RF level on the radio channel.  It is the ATRQ command.  The moment you issue the ATRQ command, it reads the RF level of any signal on the channel, and reports it back. 

To be useful, you will probably have to have some other radio transmit continuously or put a signal generator on the radio channel at the moment you issue this command. 

It is useful for determining if there is a lot of RF interference on the radio channel.  A clear interference-free channel will have a noise-floor below -120dBm. 

Also, when a data radio modem is receiving a signal, the receive signal that reaches the radio’s receiver will be weaker than the signal that reached the antenna.  The received signal will be attenuated as it travels down the coax cable to the radio’s receiver. If you want your data radio system to have the widest possible coverage, you should minimize your coax cable losses.

The amount of coax cable attenuation primarily depends upon the diameter of the cable and the dielectric material used to insulate the center conductor.  Small diameter cables are easier to install and use, but small diameter cables loose a lot more signal than the larger-diameter versions.   For cable runs less than a few feet, any cable type will do.  For coax cable runs 10-20 feet, you may consider using lower-cost middle-sized cable such as RG-58. For cable runs of over 20 feet, consider using the best quality cable you can afford (if you are trying to build a system with wide coverage and high reliability).

Coax Cable Comparison (English)

The chart above is in English units.  Below is the same data, in metric:

Coax Cable Comparison (metric)

Licenses for Data Radio Use

Raveon’s M7 radio modem operate on radio frequencies that are regulated by the Federal Communications Commission (FCC).  In order to transmit on these frequencies, you are required to have a license issued by the FCC. This article provides the information you need to obtain an FCC license for your organization

The FCC will has information to help you through the licensing process. You can find the basic information you need to begin the process at the FCC website. If you are engaged in Public Safety Radio Activities, you can go directly to:

http://wireless.fcc.gov/publicsafety

Licensees in the Industrial/Business Radio Pool are issued to radio users to support business operations. Their communications systems are used for support of day-to-day business activities, such as dispatching, AVL, and diverting personnel or work vehicles, coordinating the activities of workers and machines on location, or remotely monitoring and controlling equipment with data radio modems.  If you are a business, commercial, or institutional organization, you can go directly to:

FCC Industrial-Business Licensing

To be eligible for an FCC license in the Industrial License Pool, a person or business must use the license and be primarily engaged in any of the following activities:

• The operation of a commercial activity or business
• The operation of educational, philanthropic, or ecclesiastical institutions
• Clergy activities
• The operation of hospitals, clinics, or medical associations

In either case, you will be shown the regulations and the information you will need to gather before you get started – your desired operating frequencies, wideband/narrowband, antenna type and size, power/wattage, etc. You’ll also get information on how to obtain the necessary application forms – either in hard-copy or electronic format – and how to proceed.

The FCC website also offers a list of Frequency Coordinators. These are private organizations officially certified by the FCC to help you through the process, and who in most cases will handle the actual filing of your application. With few exceptions, you must apply for an FCC license through a Frequency Coordinator. They are located throughout the country, making it easy for you to find one that is familiar with radio operations in your area.

There are companies who specialize in assisting with licensing radio modems. You may consider contacting one of the following:

Atlas License Company and Data Services
1-800-252-0529
http://www.alcds.com

Airwaves Licensing
1-717-334-0910

http://www.airwaveslicensing.com

The when a USB device is connected to a computer, the FTDI driver software reads the device’s Vendor ID and serial number, and assigns an unused COM port number to it.   On the computer, it will create a virtual COM port, and any software that is designed to communicate with a serial device via a COM port, will be able to communicate with the Raveon data radio.  Once the FTDI device driver is installed, it will use the same COM port number for the same device plugged into the same USB port.  If the device is plugged into a different USB port on the computer, it will assign the device to a different COM port.

To force the computer to use the same COM port number for the same device, perform the following steps:

1. Connect power to the Raveon data radio modem.
2. Connect the Raveon device with the USB interface to the computer.
3. Let the computer install the device driver. Follow the on-screen instructions.

Once the device driver is installed, you can determine the COM port number that was assigned to the device by using the Windows “Device Manger“.  You can find the Device Manager utility program on most computers by selecting Start > Control Panel > System  from the System window, select the Hardware table, and click on the Device Manger button.  Expand the Ports (COM and LPT) branch to see all of the COM ports on the computer.

The COM  port for the USB serial bridge will show up in the list as “USB Serial Port (COMxx)”where COMxx is the port number assigned to the USB serial device.  The image above shows as typical listing of COM devices on a computer with 4 built-in serial ports, and one USB serial bridge.

To force the FTDI driver software to always assign the same COM port number to the same device, perform the following steps after the FTDI device driver is installed.

1. Double-click on the “USB Serial Port (COMxx)”  in the Ports branch of the Device Manger window.
2. This will open a new window showing the USB Serial Port (COMxx) Properties.
3. Select the Port Settings tab. Click on Advanced.
   
4. One the Advanced Setting for COMxx window, select the COM port Number that you would like to assign to the USB serial bridge.
   
5. Click OK.
6. On the USB Serial Port (COMxx) Properties, click OK.
7. One the Device Manager window, right click on the USB Serial Port item you just configured, and select “Disable”.
8. Once the USB Serial Port shows as disabled, right click on it again and Enable it.

The Device Manger should now show the USB Serial Port with the COM port number that you chose. 

If you unplug the USB Serial device and reconnect it, it should appear back in the Device Manager list with the correct COM port as long as you plug the same device into the same USB port.

FTDI has an application note describing how to configure the advanced settings in its device driver.  The document is FT_000073.  This application note may be helpful configuring one computer to work with multiple USB serial devices or if you need to customize your installation.

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

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.

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.

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 transciever with the optional heatsink attached is shown below.

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.