Industrial Wireless

Technical Specifications

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Industrial Wireless Technical Specifications

Advantages of Wireless Systems
Decibel (dB)
Decibel Milliwatt (dBm)
Decibel Dipole (dBd)
Decibel Isotropic (dBi)
Line of Sight (LOS)
Recieved Signal Strength Indication (RSSI)
Fade Margin
Is Line of Sight (LOS) Necessary?
Range of a 1 Watt Radio
Maximum Distance of Antenna from Radio
Minimum Distance Between 2 Antennas
Testing a Radio Link
Does Rain Affect Reception at 900 MHz?
Does Snow Affect Reception?
Are These Radios Susceptible to Interference from Cell Phones
Frequency
Yagi Antennas
Omni-Directional Antennas
TCP/IP Protocol
ModBUS Communications Protocol
Profibus
Spread Spectrum Radio

Advantages of Wireless Systems (Return to Top)
The biggest advantages of wireless are installation cost and convenience. Wireless communication systems can be installed in industrial applications at a fraction of the cost of laying cable. To install (or repair) a wired system, the expense and effort of laying cable or conduit, buying permits, hiring labor, renting machines, trenching, backfilling and more can add up. Wireless systems are easy to install and configure, saving up to 90% in project costs and drastically reducing project completion time.

Wireless solutions are also a convenient choice for unpredictable industrial environments. Systems can be tested in advance, prior to purchase and installation, to ensure suitability for a chosen application. That means you can be sure you get a solution that meets your particular needs. In applications where devices may be mobile or may be moved, wireless systems are ideal.

Decibel (dB) (Return to Top)
The basic unit of measurement used in radio signals is the decibel (dB). A dB represents the difference or ratio between two signal levels. It is typically used to describe the effect of some device on signal strength. For example, a cable can have a 6 dB of signal loss and an amplifier can have 15 dB of signal gain. This is important to know since signal strengths vary logarithmically, not linearly.

Decibel Milliwatt (dBm) (Return to Top)
A dBm represents the comparision of power levels versus 1 milliwatt. 0 dBm is defined as 1 mW (milliwatt) of power into a terminating load such as an antenna or power meter. Small signals are negative numbers (e.g. 0.1 milliwatt = - 10dBm). For example, typical 802.11b WLAN cards have +15 dBm (32mW) of output power. They also spec an 83 dBm RX sensitivity (minimum RX signal level required for 11Mbps data rate). Furthermore, 125 mW is 21 dBm and 250 mW is 24 dBm (doubling of power is +3dBm).

Decibel Dipole (dBd) (Return to Top)
A dBd represents the gain an antenna has compared to a dipole antenna at the same frequency. A dipole antenna is the smallest, least gain practical antenna that can be made. The term dBd (or sometimes just called dB, to add more confusion) generally is used to describe antenna gain for antennas that operate under 1GHz. Many antennas, especially VHF/UHF antennas, are measured in dBd if they are calibrated as a simple dipole antenna. The difference in gain (in dB) is referenced to the signal from the dipole antenna.

Decibel Isotropic (dBi) (Return to Top)
A dBi represents the gain an antenna has over a theoretical isotropic (point source) antenna. Unfortunately, making a true isotropic antenna is impossible, but mathematically they are useful for calculating theoretical fade and system operating margins. The gain of microwave antennas (above 1 GHz) is generally given in dBi. A dipole antenna has 2.15 dB gain over a 0 dBi isotropic antenna. Therefore, if an antenna gain is given in dBd, not dBi, adding 2.15 to it yields the dBi rating. For example, if an omni antenna has 5 dBd gain, it would have 5 + 2.15 = 7.15 dBi gain.

Line of Sight (LOS) (Return to Top)
Radio Frequency (RF) LOS is different that visual LOS. Visual LOS is present when one can stand next to one antenna and use binoculars to view the other antenna. RF LOS requires visual sight line between the antennas plus it also requires that a football shaped area between the two antennas be free of obstructions. This football shaped area is called the Fresnel Zone (pronounced “fray-nell” zone). The fresnel zone is an area that is larger in diameter at the center and smaller in diameter at either end. Also, the greater the distance between the antennas, the larger the diameter of the fresnel zone in the center.

Any obstructions that enter into the fresnel zone will reduce the communication range. This includes buildings, vegetation, the ground, etc. As the antennas get further apart and the diameter of the fresnel zone also increases. At longer distances the ground can begin to obstruct the fresnel zone, so in order to keep the entire fresnel zone free of obstructions it is necessary to raise the antennas.

The diameter of the fresnel zone is a function of the RF frequency and the distance between the antennas.

Recieved Signal Strength Indication (RSSI) (Return to Top)
RSSI is a way for the radio to report the strength of the radio signal it is receiving from the transmitting unit. This is an important indication of radio link quality, or how reliable the radio link is. All ioSelect industrial radios have RSSI indication.

Fade Margin (Return to Top)
The fade margin is the extra signal strength beyond what is minimally necessary for reliable reception. This extra margin is needed because the environment the radios are in is dynamic. Trees can grow, leaves can fall and regrow, and buildings can be built in the path of a radio signal. The only way to fight this is to have enough extra signal strength at the receiver so that even if these things come to pass there is still enough signal to maintain a reliable link. We suggest 10 to 20 dB of fade margin.

Is Line of Sight (LOS) Necessary? (Return to Top)
No, but it helps. The radio waves used by ioSelect pass through all kinds of obstructions just like your AM/FM radios. Wood, drywall, concrete, and steel all affect the propogation properties of radio waves differently. Wood structures are the easiest to pass through, and steel structures sometimes act as sheilds. With this in mind, to ensure radio waves penetrate or escape a conductive metal enclosure such as a steel electrical enclosure, or to get the signal into or out of a robust steel building, we recommend mounting the antenna on an external surface and connecting it to the radio inside with an appropriate RF cable.

Range of a 1 Watt Radio (Return to Top)
That depends on the gain of the antennas used and the nature or density of obstructions in the path. Here are a few guidelines to keep in mind:

  • 1000' (1/5 of a mile) in a heavily obstructed industrial or municipal setting using 1/4 wave, 0 dB gain omni-directional antennas.

  • 1000' (1/5 of a mile) to 1 mile in mildly obstructed industrial or municipal settings using 1/4 wave, 0 dB gain omni-directional antennas and smart antenna placement.

  • 1 to 2 miles Line of Sight with 1/4 wave, 0 dB gain omni antennas.

  • 1 mile through a dense forest of hardwood trees or across an industrial plant using 6 dB gain antennas (on both ends).

  • 2 to 20+ miles if you have Line of Sight and you can increase the antenna height as the distance increases (higher the better).

Maximum Distance of Antenna from Radio (Return to Top)
Generally 200 feet is a practical maximum. Like all cable, as the length of your coaxial RF cable increases so does signal loss. Similarly, there are several types of coaxial RF cable which vary in attenuation properties depending on quality and price. Rule of thumb: running antenna cable is very similar to running 120 V wire, as the length increases you must increase the cable diameter to compensate for the voltage (signal) loss.

Minimum Distance Between 2 Antennas (Return to Top)
Separate the antennas either 6 feet vertically or 10 feet horizontally.

Testing a Radio Link (Return to Top)
Under conditions when the most obstructions are in place. This means in the spring/summer if there are leaf bearing trees (add a 5-10 dB of additional signal attenuation if testing in the winter) or when the doors to a facility are closed (if transmitting from outside to inside a building).

Does Rain Affect Reception at 900 MHz? (Return to Top)
Typically, radio designers ignore the effects of precipitation at frequencies below 1 GHz. However, practical experience has shown some receive signal strength variations in heavy rain storms, possibly due to water vapor in the path or antenna connections not being water tight. This is why we recommend that all installations have a 10-20 dB fade margin.

Does Snow Affect Reception? (Return to Top)
Snow flakes themselves will not attenuate a 900 MHz radio signal, however snow and ice build-up on an antenna, change its shape, and therefore change is propogation characteristics. To overcome this, most antennas have a fiberglass radome that prevents snow from contacting the metal radiating elements. Yagi antennas are mounted with vertical polarization (cross bars vertical) to minimize snow build-up. These preventative measures have allowed radio based SCADA systems for water/waste water utilities and oil & gas applications to be used reliably in the most northerly cities and outlying areas for decades.

Are These Radios Susceptible to Interference from Cell Phones (Return to Top)
No. Cell phones operate on frequency bands, typically 860 to 890 MHz and 1.8 GHz, outside the ISM 900 MHz band where the ioSelect industrial radios operate. The fixed frequency voice radios that plant personnel use often operate in the 450 MHz range. In terms of off-band interference, the ioSelect industrial radios use narrow band filters to keep unwanted signals out. That said, other ISM band radios operating within the 900 MHz band do have the potential to cause interference, but because of the nature of frequency hopping radios, if a collision occurs on one frequency, milliseconds later the radios hop to other frequencies where data can be updated.

Frequency (Return to Top)
This is the key identifier for a radio. The frequency that a radio operates at defines if the system is license free or if a license from the regulation body is required (such as FCC - Federal Communications Commission). There are three main license free bands: 900 MHz, 2.4 GHz, and 5 GHz. These are callled the ISM (industrial, scientific, and medical) bands, the FCC requires that a radio operate within specific guidelines including some spread spectrum technology.

Yagi Antennas (Return to Top)
These are directional antennas that are designed to achieve a very substantial increase in the antenna's directionality and gain compared to other types of antennas. There are three parts that make up a Yagi antenna, the driven element, the director, and the reflector. We are more concerned about the type of gain we can obtain from a Yagi antenna. The number of elements is one of the main factors. Typically a reflector is the first element added in any yagi design as this gives the most additional gain. Directors are then added. Next is the element spacing, typically a wide spaced beam, one with wide spacing between the elements gives more gain than one that is more compact. The most critical element positions are the reflector and first director. Finally, the antenna length, has been shown that gain is proportional to the length of the array.

Omni-Directional Antennas (Return to Top)
This type of antenna radiates radio waves in all directions in one plane. The power decreases at the elevation angle above or below the plane, where zero power is on the antenna's axis. This type of antenna can deliver very long communication distances. Rubber Ducky or whip antenna is one type of omni directional antenna, but with low or zero gain. The higher gain omni directional antennas are coaxial collinear antennas.

TCP/IP Protocol (Return to Top)
TCP/IP, also known as Transmission Protocol and Internet Protocol, are the first networking protcols defined in this standard. Communications are separated into various layers: link, internet, transport, and application layer. The layers define the operational scope, each has their own functionality that solves a set of problems in its scope. The link layer is for communication for the local network where the host is connected. The internet layer manages the connections within the local network and establishes the internet. The transport layer handles host to host communication tasks. The last layer, the application layer contains protocols that are defined for each of the data communication services and application based interaction between the internet hosts.

ModBUS Communications Protocol (Return to Top)
The ModBUS protocol is a messaging structure that is used to establish a master-slave or client-server communication. It is a truly open and widely used network protocol in the industrial manufacturing world. Applications include but are not limited to buildings, infrastructures, transportation, and energy applications. It is a serial communication protocol used widely with programmable logic controllers (PLCs). It has been developed with the industrial world in mind, openly published, easy to deply and maintain, and minimal restrictions. Many devices on the same network can all communicate together. Versions include ModBUS RTU, ModBUS TCP/IP, and ModBUS ASCII. Each device that communicates via ModBUS has its own unique address in order to communicate with the Master (is the only device that can initiate a command in serial and MB+ networks). Any device on Ethernet can send out a ModBUS command. When a Master sends out a command, only the intended device will respond.

Profibus (Return to Top)
Also known as Process Field Bus is a standard for field bus communications. There are two types, Profibus DP and Profibus PA. DP (Decentralized Peripherals) is used to operate sensors from a central location for automation applications. PA (Process Automation) is used to monitor measuring equipment from a system. This version is designed to be used in explosive and hazardous environments.

Spread Spectrum Radio (Return to Top)
This type of radio uses a technique where the signal generated in a specific bandwidth is deliberately spread across the frequency domain. This type of method creates a secure communication, increased resistance to natural interference/noise, and to prevent detection. More specifically a FHSS radio (Frequency Hopping Spread Spectrum) rapidly switches a carrier among frequency channels. Only the transmitter and receiver know the sequence, which increases security of the signal. There are 3 main advantages: highly resistant to narrowband interference, difficult to intercept, and can share a frequency band with many types of conventional transmissions creating efficient use of the bandwidth.