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How to Obtain an FCC License for Narrow-band Data Radio

Obtaining an FCC license to use a narrow-band radio channel is not difficult at all.  In fact, the FCC has listed over 300 ,000 license holders in the Land Mobile Radio service alone.

Licenses for Data Radio Use

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

1901 Pennsylvania Ave., N.W., Suite 500
Washington, DC 20006
P: 202-872-0030
F: 202-872-1331
Central Station Alarm Association (CSAA)
Attn: Robert Bitton, President
1565 Union Avenue, P.O. Box 775
Union, New Jersey 07083-0775
P: 908-810-8822
F: 908-810-8844
1565 Oak Street
Eugene, Oregon 97401
P: Main Office: 541-485-8441
P: Chicago: 888-583-2-WAY
P: Dallas: 888-342-2-WAY
P: Los Angeles 888-355-2-WAY
P: WASH. D.C. 888-395-2-WAY
F: 541-485-7556
899-A Harrison St., S.E.
Leesburg, VA 20175
P: 703-669-0320
F: 703-669-0322

The FCC Licensing Process

  1. Gathering Information
    (Frequency band you wish to use, number of radios you will use, determine the desired RF power output level, location of the base-station, the base-station antenna height and supporting structure, base station site elevation above sea level (meters), and the emission designator (11K0F1D for the M7 radio).
  2. Choose a Frequency Coordination
    Frequency coordinators
    are FCC certified to recommend the most appropriate frequencies for applicants in the designated Part 90 radio services. Choose one from the list above, or Google “FCC Industrial Frequency Coordinators” to find one you would like to work with.
  3. File The Application
    Applications are normally filed with the FCC through the frequency coordinator.  The frequency coordinator you choose will file the application with the FCC.
  4. Immediate Operation
    There are two ways to begin immediate operation of your system. The FCC implemented a licensing procedure for conditional authority in 1995. You may begin operating your system 10 days after your application is filed with the FCC. In addition, you may apply for a Special Temporary Authority to operate during emergency or other urgent conditions without filing a license application.
  5. Notification of Construction
    A licensee must notify the Commission that its system is constructed and placed into operation within 12 months of the date of grant or their license will automatically cancel. Notification is made by filing FCC Form 601 through ULS (Purpose Code: NT). You may also request an extension.
  6. Renewal of License
    Your FCC license will typically be issued for 10 years.  You must file for renewal of your license no later than the expiration date of your license period, and no sooner than 90 days prior to expiration by filing FCC Form 601 (Purpose Code: RO) through ULS. (See 47 CFR 1.949).

Sleep Mode 1 in the M7 Data Radio

In the M7 radio, Sleep Mode 1 is enabled with the ATSM 1command.  There also must be 3 components installed on the circuit board of the M7 radio to allow sleep mode 1 to work. It is highly recommended that this modification be done at Raveon, or by very qualified technician skilled in fine-pitch soldering.  Damage to the M7 due to the installation of this modification by a customer is not covered under warranty. 

When the three components are installed, the DTR line on the RS232 serial port may be used to turn the M7 data radio on and off.  The three components are R43, C21, and R12.  R43 should be a 1K 0603 resistor.  R12 should be a 10K 0603 resistor, and C21 should be a 680pF 0603 ceramic capacitor, 50V rated.

I/O Circuit

M7 I/O Circuit Schematic

To access the three components, the main circuit board in the M7 must be carefully removed.  Remove the 4 screws securing the front pannel, the two screws on the side and the four screws that hold the back panel on.  Then removed the one screw on the bottom of the unit that secures the voltage regulator.  Slide the PCA out of the enclosure.   

The location of the three components on the printed circuit board is shown below:

Once these components are installed, the DTR input will control the power supply of the M7 radio. If DTR input is below about 0.8V, the M7 radio will power off.  If DTR goes above about 3 V, the radio will power on.  In Sleep Mode 1, and external device must control the DTR line.  The radio cannot turn itself on or off.  If nothing is connected to the RS 232 serial port, the radio will be turned off, because R12 is a pull-down resistor, and will cause the radio to turn off if no signal drives the DTR line.

Once the modification is complete, re-assemble the M7 in hte reverse order is was disassembled.

MIMIC Wireless Remote Control for power and AC devices

To easily do Wireless Pump Control, AC light control, and many other remote control applications, Raveon has added a “MIMIC” mode to the M7 series of data radio modems and to the Tech Series (RV-M21 RV-M22) data radio modems. It works for not only wireless pump control, but also to remotely control most any electrical device that is turned on and off with a switch or relay.

The MIMIC mode allows two or more data radio modems to “mimic” each other’s digital I/O.  When in the MIMIC mode, the M7 will periodically transmit its digital status.  The modem will also continue to operate as a radio modem, sending/receiving data using pins 2&3 of the DB9, but the other I/O pins of the DB9 will be used for digital input/output. The MIMIC mode also has a fail-safe setting, so that in the event the radio link is broken, the receiving MIMIC radio will automatically set the MIMIC output to a pre-defined state.

Normally, the Serial I/O connector operates like an RS232 serial interface.  If the MIMIC mode is enabled, the operation of the radio is modified to transmit the digital status of the INPUT0 and INPUT1 pins across the radio link, and output their status on the OUT0 and OUT1 pins.

 MIMIC  GPIO or FIO  IO Pins

The Tech Series data radio modems have General Purpose IO (GPIO) and Flexible digital IO (FIO) front panel options that are great for wireless long-range MIMIC signals.

 MOSFET Driver

The Tech series radio modems (RV-M21 and RV-M22) have a MOSFET output driver on the GPIO Out 0 output.  Out 0 will be pulled to ground to energize an external relay or lamp whenever OUT0 was supposed to go low.  So closing S1 on the sending station will cause OUT0 to go low, energizing the relay/lamp/led…

The MOSFET output drives OUT 0, pulling it to ground.  Do not connect a lamp/relay that draws more than specified output current.  Also, if driving an inductive load, use a surge-protection diode such as a 1N4001 across the load to prevent high-voltage transients.

If the MOSFET driver is used, Output 0 will simply follow Input 0 with RS232 signal levels or inputs from GPIO of FIO.

In the RV-M7 data radio, MIMIC mode will work without the optional MOSFET, but if you want the M7 radio do drive one relay or medium-current device, then you must order the MOSFET option for OUT0 from the factory when the M7 is purchased.

MIMIC Hardware

There are two aspects to the MIMIC mode:

  1. The transmitter that sends the status of its digital inputs.  This is enabled with the MIMIC X Y command.
  2. The unit that receives the over-the-air MIMIC message, and sets its digital outputs to match the inputs of the sending station.  This function is enabled with the ATIO 1 command.  ATIO 1 configures the DB9 serial port to operate with RS232 signal levels, and use the digital control lines for digital I/O instead of RS232 flow control.  ATIO 0 turns off MIMIC reception ability, and the digital I/O pins will operate as flow control signals.

The goal of the MIMIC mode is quite simple: Flip a switch at one location, and have something at another location turn on or off.

Configuring a Modem for MIMIC mode

MIMIC transmissions are enabled with the MIMIC X Y command.   MIMIC 0 disables MIMIC mode and puts the unit in standard radio modem operation mode.  MIMIC X Y with X and Y being any positive number will enable the MIMIC feature. The MIMIC X Y command sets the unit to transmit a MIMIC over-the-air message every X seconds when INPUT0 is low, and to every Y seconds when INPUT0 is high.

For a remote modem to receive the MIMIC message and output it in that slave device, use the FAILSAFE A B command to setup the safe parameters for the Slave outputs. The Slave output MIMIC the Master’s inputs, but it communication were to fail, the FAILSAFE setting will take over. Slaves must have FAILSAFE setup.

For complete details on configuring an M7 for MIMIC mode, see application note AN161_MIMIC_M7.

MIMIC Command settings

If digital input INPUT0 is low, every X seconds, the M7 will automatically transmit the digital status of both the the INPUT0 and INPUT1 pins.  If INPUT0 is high, every Y seconds, the M7 will automatically transmit the digital status of the INPUT0 and INPUT1 pins. For example, MIMIC 2 60 configures the radio to send the state of INPUT0 and INPUT1 pins every 2 seconds if INPUT0 is low, and every minute if INPUT0 is high.

Radio addressing operates as it does in the standard mode.  When a unit receives a MIMIC transmission intended for its ID, it will set its OUT0 and OUT1 pins as determined by the sending stations INPUT 0 and INPUT1.

When the unit is in the Command mode, MIIC transmissions will not take place. The command mode is entered by sending +++ into the serial port.  See the M7 Technical Manual for information on how to configure the M7 using the built-in commands.

The MIMIC transmissions are the same over-the-air format as a standard data transmission from an M7 radio modem, except they contain no user-data, only digital I/O information.  An M7 radio modem configured as a repeater will repeat the MIMIC messages.

Failsafe Settings

To ensure failsafe operation, a FAILSAFE A B command sets the minimum message interval, and the default digital output state if an over-the-air MIMIC message is not received within the failsafe period.  A is the minimum period, and B is the ASCII hex value of the digital outputs if the failsafe interval passes and no MIMIC messages are receive.  B is also the power-on default value of the digital outputs.

For example, FAILSAFE 60 1 configures the unit to require a MIMIC message at least every minute. If one is not received within 60 seconds, OUT0 will go high (open drain), and OUT1 will go low (below ground).

It is recommended that the A value for the FAILSAFE command be about 2.5 times longer than the largest of the X and Y values of the MIMIC command.  This allows for one MIMIC message to be missed.  For example if MIMIC transmissions are set to MIMIC 2 60, a reasonable FAILSAFE A B setting would be a value of 150 for A. This will allow one MIMIC message to be missed and the FAILSAFE value not kick in. If more than two MIMIC messages did not get received, after 150 seconds, the M7 would revert to the failsafe values.

Wireless Pump Control

To easily do Wireless Pump Control, Raveon has added a “MIMIC” mode to the M7 series of data radio modems. It works for not only wireless pump control, but also to remotely control most any electrical device that is turned on and off with a switch or relay. The MIMIC mode allows two or more M7 data radio modems to “mimic” each other’s digital I/O.  When in the MIMIC mode, the M7 will periodically transmit its digital status.  The M7 will also continue to operate as a radio modem, sending/receiving data using pins 2&3 of the DB9, but the other I/O pins of the DB9 will be used for digital input/output. The MIMIC mode also has a fail-safe setting, so that in the event the radio link is broken, the receiving MIMIC radio will automatically set the MIMIC output to a pre-defined state. Normally, the Serial I/O connector operates like an RS232 serial interface.  If the MIMIC mode is enabled, the operation of the radio is modified to transmit the digital status of the INPUT0 and INPUT1 pins across the radio link, and output their status on the OUT0 and OUT1 pins. There are two aspects to the MIMIC mode:

  1. The transmitter that sends the status of its digital inputs.  This is enabled with the MIMIC X Y command.
  2. The unit that receives the over-the-air MIMIC message, and sets its digital outputs to match the inputs of the sending station.  This function is enabled with the ATIO 1 command.  ATIO 1 configures the DB9 serial port to operate with RS232 signal levels, and use the digital control lines for digital I/O instead of RS232 flow control.  ATIO 0 turns off MIMIC reception ability, and the digital I/O pins will operate as flow control signals.

The goal of the MIMIC mode is quite simple: Flip a switch at one location, and have something at another location turn on or off.

Pivot Irrigation Systems using Raveon Data Radios

Raveon Technologies RV-M7 UHF radios provide an excellent communications link for Pivot Irrigation Systems using UHF and VHF radio modems.

In the course of maximizing crop yield, daylight hour efficiency, and limited natural resources, farmers today must utilize every technology available that gives them an advantage in the market place. To attain this advantage, however, it must come with a transparent technology approach so the farmer can focus on his expertise and strengths and allow the technology to operate seamlessly. Pivot Irrigation systems employing Raveon Technologies UHF or VHF GPS enabled radio solutions provide just that balance to the farmer.

As pivot irrigation systems improved farming efficiencies by an order of magnitude decades ago, adding “smart communications” to the irrigator is the next logical step. Data such as moisture, pivot location, weather, operability, and failure/faults which where once gathering by the farmer entering the field and making a visual inspection, can now be effectively done at the farmhouse (or even further away) using low cost UHF GPS enabled radios. Data can also be tracked and stored to be reviewed between growing seasons to better improve next year’s yields.

Two main methods of radio communications have been employed, cellular and UHF. VHF/UHF data radio modems far and away trumps cellular due to the fact that there are no monthly recurring data charges along with higher reliability as there are no risks of losing a signal due to heavy phone traffic volume. Add to the fact that UHF can transmit much farther (up to 50 miles), can send/receive unlimited data without added charges, operate in grid power failure modes, and be free of annual cell contracts that are inefficient in short Upper Midwest growing seasons (where data transmission may only be required for as little as four months), the choice of radio communication becomes obvious.

The Raveon Technologies RV-M7-U-GX radio modem solves the radio decision by providing highly reliable, ruggedized, low power, precise GPS enabled radio control operating in the licensed UHF frequency band (450-470Mhz.). The M7 is ideally suited as it is a proven design with a proven track record, has shipped in volume production for seven years, and has a low system and operating cost. Raveon’s RV-M7-UC data radio modem has all of the features of the RV-M7-U-GX except the internal GPS receiver.  It is ideal for sending/receiving data, remote control, reading remote sensors, and any other data communication need where GPS position information is not requried.

The systems solution includes the pivot irrigator itself, sensors that monitor weather, moisture, fault, pivot arm position, etc. along with the Raveon Technologies RV-M7-U-GX to perform radio communications. To complete the bidirectional link, a second RV-M7 radio along with a PC would be placed at the farmhouse for monitoring and control.

With the system in place, the farmer from the farmhouse or base station can monitor and adjust the exact position of the pivot arm, adjust for irregular shaped fields, water only when water is needed, change watering cycles during the changing growing season, spot a fault or failure with the pivot long before any crop damage can occur, flag locations of concern for visual inspection, and can store and save statistics and data to be reviewed between growing seasons.

In summary, Raveon Technologies low cost UHF radios provide a highly reliable data link between farmer and pivot irrigator to enable new levels of efficiency and crop management in modern farming.

Raveon Technologies is located in Vista, Ca. They can be reached at www.raveontech.com or 760-727-8004.

USB Port Assignments

The M7-USB option, and all of the USB serial bridge cables from Raveon use the FTDI FT232R chip-set.  Raveon has an application note <here> that describes how the M7-USB option works.  The driver for the FTDI chipset is included with most versions of Microsoft Windows, and it may be <Downloaded Here>.

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.

 

 

Lost Password

M7 series products with firmware version C0 or higher have the ability to password protect the user interface. If it is password protected, the radio will output a “password:” prompt when entering the command mode.
When in the command mode, to enable the use of a password enter:
Password xxxx
Where xxxx is the 2-7 digit password you would like to protect the user interface with.
To disable password protection, enter:
Password 0 (zero not oh)
Note: If the user-interface is password protected, and the Config button on the M7 is pressed, for security reasons, the encryption phrase is automatically erased.

To Reset the Password:

If you forget what the password is, you will have to reset the password. To do this:

  1. Remove the back plate off of the M7 radio.
  2. With the power on, momentarily press the Config button
  3. You will get an OK prompt back from the radio, and it will be in the command mode.
  4. Enter Password 0 to erase the password, and disable the password feature.
  5. To store a new password, issue a Password xxxx command where xxxx is the new 2-7 digit password.

C12 Software Release Note (M7 Series)

New features and fixes

  • The  “/” key can now be used to repeat the previous command.
  • Added login capability with password protection.
    • If the password is set, login is required.
    • The PASSWORD command will set the password and PASSWORD 0 will disable it.
  • Added an extended speed field to the standard GPS position report. Speeds > 255km/h are now supported and will add one byte over-the-air
  • Modified behavior of the REPEAT 1 command.  After using it, everything will be repeated, and entries 2-4 in the table are erased
  • WMX message output now contains an RSSI field
  • A CRC is now always required over-the-air. This change is transparent to users but increases reliability
  • TDMA slots now have a 10mS resolution
  • GPS 5 (-LX) now defaults to $PRAVE instead of WPL
  • Carrier detect level can now be set with the ATCD command. The default is -113dBm.
  • The ATRA command has been removed
  • TRIGBITS now latch- e.g. if set for high, they will always be transmitted high once
  • If TXRATE=0 and IDLERATE=0, then unit will now not report at all
  • GGA and RMC position messages can now be selected via OUTPUT 11 and 12 commands.
  • The default serial rate is now 9600 baud
  • AT&F saves all commands now. Previously an ATSV command was required
  • All UTC times ($PRAVE, etc) are now always 6 digits, with leading zeros.
  • VTG output messages are now turned on in GPS mode 13
  • VTG and GLL messages can now be turned out with OUTPUT 14

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 and all narrow-band 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 GPS tracking Data Radio modem 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.