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 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.

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. 

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>

In a traditional wired SCADA system, a device is monitored by some type of computer or other human-to-machine interface.  The user may have something as simple as an LED indicator, or as complex as a computer server for the operator.  The human interface communicates to another electronic device that is remotely located at the Central Monitoring Station. Often this remote device is a Remote Terminal Unit (RTU) or Programmable Logic Controller (PLC).

Typical SCADA System

When the distance between the central monitoring station and the device being monitored is not trivial, then a wireless link between the two sites becomes a logical means of connecting them.

Raveon’s UHF data radio modems  and VHF data radio modems are well suited for very long range wireless SCADA systems.  They use licened narrow-band radio frequencies, and output up to 5 watts of rf power on either UHF or VHF radio bands.  Communication distances of many miles is usually easy to achieve, and with proper system design, 20-100 miles is achievable.