AIR-ANT2566P4WR-RF

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AIR-ANT2566P4WR-RF

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Cisco Refurbished
Original Part No : AIR-ANT2566P4W-R=

2.4GHz 6dBi/5GHz6dBiDirectionalAnt.4pt,RP-TNC REMANUFACTURED
AED 0

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Available Quantity: 759

Delivery Time: 2 to 4 week

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    Overview

    Executive Overview

    This antenna reference guide explains issues and concerns about antennas used with a Cisco® Aironet®wireless LAN system or wireless bridge system. It details deployment and design, limitations and capabilities, and basic theories ofantennas. This document also contains information about the Cisco antennas and accessories, as well as installation scenarios, regulatory information, and technical specifications and diagrams of the available antennas.

    Overview of Antennas

    Each Cisco Aironet radio product is designed to perform in a variety of environments. Implementing the antenna system can greatly improve coverage and performance.

    To optimize the overall performance of a Cisco wireless LAN, it is important to understand how to maximize radio coverage with the appropriate antenna selection and placement. An antenna system comprises numerous components, including the antenna, mounting hardware, connectors, antenna cabling, and in somecases, a lightning arrestor. For a consultation, please contact a Cisco Aironet partnerat: http://tools.cisco.com/WWChannels/LOCATR/jsp/partner_locator.jsp.

    Cisco partners can provide onsite engineering assistance for complex requirements.

    Radio Technologies

    In the mid-1980s, the U.S. Federal Communications Commission (FCC) modified Part 15 of the radio spectrum regulation, which governs unlicensed devices. The modification authorized wireless network products to operate in the industrial, scientific, and medical (ISM) bands using spread spectrum modulation. This type of modulation had formerly been classified and permitted only in military products. The ISM frequencies are in threedifferent bands, located at 900 MHz, 2.4 GHz, and 5 GHz. This document covers both the 2.4- and 5-GHzbands.

    The ISM bands typically allow users to operate wireless products without requiring specific licenses, but this will vary in some countries. In the United States, there is no requirement for FCC licenses. The products themselves must meet certain requirements to be certified for sale, such as operation under 1-watt transmitter output power (in the United States) and maximum antenna gain or effective isotropic radiated power (EIRP) ratings.

    The Cisco Aironet product lines utilize both the 2.4- and 5-GHz bands. In the United States, three bands are defined as unlicensed and known as theISM bands. The ISM bands are as follows:

    ● 900 MHz (902-928 MHz)

    ● 2.4 GHz (2.4-2.4835 GHz) - IEEE 802.11b

    ● 5 GHz (5.15-5.35 and 5.725-5.825 GHz) - IEEE 802.11a, HIPERLAN/1 and HIPERLAN/2. This band is also known as the UNII band, and has threesubbands: UNII1 (5.150-5.250 GHz), UNII2 (5.250-5.350 GHz), and UNII3 (5.725-5.825 GHz)

    Each set of bands has different characteristics. The lower frequencies exhibit better range, but with limited bandwidth and hence lower data rates. The higher frequencies have less range and are subject to greater attenuation from solid objects.

    802.11 Modulation Techniques

    The IEEE 802.11 standard makes provisions for the use of several different modulation techniques to encode the transmitted data onto the RF signal. These modulation techniques are used to enhance the probability of the receiver correctly receiving the data and thus reducing the need for retransmissions. The techniques vary in their complexities and robustness to RF signal propagation impairments.

    Direct-Sequence Spread Spectrum

    The direct-sequence spread spectrum (DSSS) approach involves encoding redundant information into the RF signal. Every data bit is expanded to astring of chips called a chipping sequence or Barker sequence. The chipping rate, as mandated by the U.S. FCC, is 10 chips atthe 1- and 2-Mbps rates and 8 chips at the 11-Mbps rate. So, at 11 Mbps, 8 bits are transmitted for every one bit of data. The chipping sequence is transmitted in parallel across the spread spectrum frequency channel.

    Frequency-Hopping Spread Spectrum

    Frequency-hopping spread spectrum (FHSS) uses a radio that moves or hops from one frequency toanother at predetermined times and channels. The regulations require that the maximum time spent on any one channel is 400 milliseconds. For the 1- and 2-Mb FHSS systems, the hopping pattern must include 75 different channels, and must use every channel before reusing any one. For wide-band frequency hopping (WBFH) systems, which permit up to 10-Mb data rates, the rules require the use of at least 15 channels, and they cannot overlap. With only 83 MHz of spectrum, WBFH limits the systems to 15 channels, thus causing scalability issues.

    In every case, for the same transmitter power and antennas, a DSSS system will have greater range, scalability, and throughput than an FHSS system. Forthis reason, Cisco has chosen to support only direct-sequence systems in the spread spectrum products.

    Orthogonal Frequency Division Multiplexing

    The orthogonal frequency division multiplexing (OFDM) used in 802.11a and 802.11g data transmissions offers greater performance than the older direct-sequence systems. In the OFDM system, each tone is orthogonal to the adjacent tones and therefore does not require the frequency guard band needed for direct sequence. This guard band lowers the bandwidth efficiency and wastes up to 50 percent of theavailable bandwidth. Because OFDM is composed of many narrow-band tones, narrow-band interference degrades only a small portion of the signal, with little or no effect on the remainder ofthe frequency components.

    Antenna Properties and Ratings

    An antenna gives the wireless system three fundamental properties - gain, direction, and polarization. Gain is a measure of increase inpower.Direction is the shape of the transmission pattern. A good analogy for an antenna is the reflector in a flashlight. The reflector concentrates and intensifies the light beam in a particular direction similar to what a parabolic dish antenna would do to a RF source in a radiosystem.

    Antenna gain is measured in decibels, which is a ratio between two values. The gain of a specific antenna is compared to the gain of an isotropic antenna. An isotropic antenna is a theoretical antenna with a uniform three-dimensional radiation pattern (similar to a light bulb with no reflector). dBi is used to compare the power level of a given antenna to the theoretical isotropic antenna. The U.S. FCC uses dBi in its calculations. An isotropic antenna is said to have a power rating of 0 dB, meaning that it has zero gain/loss when compared to itself.

    Unlike isotropic antennas, dipole antennas are real antennas. Dipole antennas have a different radiation pattern compared to isotropic antennas. The dipole radiation pattern is 360 degrees in the horizontal plane and 75 degrees in the vertical plane (assuming the dipole antennais standing vertically) and resembles a donut in shape. Because the beam is “slightly” concentrated, dipole antennas have a gain over isotropic antennas of 2.14 dB in the horizontal plane. Dipole antennas are said to have a gain of 2.14 dBi (in comparison to an isotropic antenna).

    Some antennas are rated in comparison to dipole antennas. This is denoted by the suffix dBd. Hence, dipole antennas have a gain of 0 dBd (=2.14 dBi).

    Note that the majority of documentation refers to dipole antennas as having a gain of 2.2 dBi. Theactual figure is 2.14 dBi, but is often rounded up.

    Types of Antennas

    Cisco offers several different styles of antennas for use with access points and bridges inboth 2.4-GHz and5-GHz products. Every antenna offered for sale has been FCC-approved. Each type of antenna will offer different coverage capabilities. As the gain ofan antenna increases, there is some tradeoff to its coverage area. Usually high-gain antennas offer longer coverage distances, but only in a certain direction. The radiation patterns below will help to show the coverage areas of the styles of antennas that Cisco offers: omnidirectional, Yagi, and patch antennas.

    Omnidirectional Antennas

    An omnidirectional antenna (Figure 1) is designed to provide a 360-degree radiation pattern. This type of antenna is used when coverage inall directions from the antenna is required. The standard 2.14-dBi “Rubber Duck” is one style of omnidirectional antenna.

    Figure 1. Omnidirectional Antenna

     

    Directional Antennas

    Directional antennas come in many different styles and shapes. An antenna does not offer any added power to the signal; it simply redirects the energy it receives from the transmitter. By redirecting this energy, it has the effect of providing more energy in one direction, and less energy in all other directions. As the gain of a directional antenna increases, the angle of radiation usually decreases, providing a greater coverage distance, but with a reduced coverage angle. Directional antennas include patch antennas (Figure 2), Yagi antennas (Figure 3), andparabolic dishes. Parabolic dishes have a very narrow RF energy path, and the installer must be accurate in aiming these types of antennas these at each other.

    Figure 2. Directional Patch Antenna

     

    Figure 3. Yagi Antenna

     

    Diversity Antenna Systems

    Diversity antenna systems are used to overcome a phenomenon known as multipath distortion or multipath interference. A diversity antenna system uses two identical antennas, located a small distance apart, to provide coverage to the same physical area.

    Multipath Distortion

    Multipath interference occurs when an RF signal has more than one path between a receiver and a transmitter. This occurs in sites that have a large amount of metallic or other RF reflective surfaces.

    Just as light and sound bounce off of objects, so does RF. This means there can be more than one path that RF takes when going from a transmit (TX) and receive (RX) antenna. These multiple signals combine in the RX antenna and receiver to cause distortion of the signal.

    Multipath interference can cause the RF energy of an antenna to be very high, but the data wouldbe unrecoverable. Changing the type of antenna and location of the antenna can eliminatemultipath distortion (Figure4).

    Figure 4. Multipath Distortion

     

    You can relate multipath distortion to a common occurrence in your car. As you pull up to a stop, you may notice static on the radio. But as you move forward a fewinches or feet, the station starts to come in more clearly. By rolling forward, you move the antenna slightly, out of the point where the multiple signals converge.

    How Diversity Antenna Systems Reduce Multipath Distortion

    A diversity antenna system can be compared to a switch that selects one antenna or another, never both at the same time. The radio in receive modewill continually switch between antennas listening for a valid radio packet. After the beginning sync of a valid packet is heard, the radio will evaluate the sync signal of the packet on one antenna, and then switch to the other antenna and evaluate. Then the radio will select the best antenna and use only that antenna for the remaining portion of that packet.

    On transmit, the radio will select the same antenna it used the last time it communicated to thatgiven radio. If a packet fails, it will switch to the other antenna and retry the packet.

    One caution with diversity antenna systems is that they are not designed for using two antennas covering two different coverage cells. The problem in using it this wayis that ifantenna number 1 is communicating to device number 1 while device number 2 (which is in the antenna number 2 cell) tries to communicate, antenna number 2 is not connected (due to the position of the switch), and the communication fails. Diversity antennas should cover the same area from only a slightly different location.

    With the introduction of the latest direct-spread physical layer chips, and the use of diversity antenna systems, direct-spread systems have equaled or surpassed frequency-hopping systems inhandling multipath interference. While the introduction of WBFH does increase the bandwidth of frequency-hopping systems, it drastically affects the ability tohandle multipath issues, further reducing its range compared to present direct-spread systems in sites that are highly RF reflective.

    Wireless LAN Design

    Before the physical environment is examined, it is critical to identify the mobility of the application, the means for coverage, and system redundancy. An application such as point-to-point, which connects two or more stationary users, may be best served by a directional antenna, while mobile userswill generally require a number of omnidirectional micro cells. These individual micro cells can be linked together through the wired LAN infrastructure or by using the wireless repeater functionality built into every Cisco Aironet access point.

    The Physical Environment

    After mobility issues are resolved, the physical environment must be examined. While the area of coverage is the most important factor for antenna selection, it is not the sole decision criterion. Building construction, ceiling height, internal obstructions, available mounting locations, andthe customer’s aesthetic desires also must be considered.

    Cement and steel construction have different radio propagation characteristics. Internal obstructions such as product inventory and racking in warehousing environments are factors. In outdoor environments, many objects can affectantenna patterns, including trees, vehicles, and buildings, to name a few.

    The Network Connections

    Cisco Aironet access points use a 10/100/1000-Mb Ethernet connection. Typically the access point is in the same location as the antenna. While it may seem that thebest place to put the access point is in a wiring closet with the other network components, such as switches, hubs, and routers, this is not the case. The antenna must be placed in an area that provides the best coverage (determined by a site survey).

    Many people new to wireless LANs want to locate the access points in the wiring closet and connect the antenna using RF coax. Antenna cable introduces losses in the antenna system on both the transmitter and the receiver. As the length of cable increases, so does the amount of loss introduced. To operate at optimum efficiency, cable runs should be kept as short as possible. (See the Cabling section in this document for more information.)

    Building Construction

    The density of the materials used in a building's construction determines the number of walls the RF signal can pass through and still maintain adequate coverage. Following are a few examples. The actual effect on the RF must be tested at the site, and therefore a site survey is recommended.

    Paper and vinyl walls have very little effect on signal penetration. Solid walls and floors and precastconcrete walls can limit signal penetration to oneor two walls without degrading coverage. This may vary widely based on any steel reinforcing within the concrete. Concrete and concrete block walls may limit signal penetration to three or four walls. Wood or drywall typically allow for adequate penetration through five or six walls. A thick metal wall reflects signals, resulting in poor penetration. Steel-reinforced concrete flooringwill restrict coverage between floors to perhaps one or two floors.

    Recommendations for some common installation environments are outlined below:

    ● Warehousing/manufacturing: In most cases, these installations require a large coverage area. Experience has shown that an omnidirectional antenna mounted at 20 to 25 feet typically provides the best overall coverage. Of course, this also depends upon theheight of the racking, material on the rack, and ability to locate the antenna at this height. Mounting the antenna higher will sometimes actually reduce coverage, as the angle of radiation from the antenna is more outward than down. The antenna should beplaced in the center of the desired coverage cell and in an open area for best performance. In cases where the radio unit will be located against a wall, a directional antenna such as a patch or Yagi can be usedfor better penetration of the area. The coverage angle of the antenna will affect the coverage area.

    ● Small office/small retail store: The standard dipole may provide adequate coverage in these areas depending on the location of the radio device. However, in a back corner office a patch antenna may provide better coverage. It can be mounted to the wall above most obstructions for best performance. Coverage of this type antenna depends on the surrounding environment.

    ● Enterprise/large retail store: In most cases, these installations require a large coverage area. Experience has shown that omnidirectional antennas mounted just below the ceiling girders or just below the drop ceiling typically provide the best coverage (this will vary with stocking, type of material, and building construction). The antenna should be placed in the center of the desired coverage cell and in an open area for best performance. In cases where the radio unit will be located in a corner, or at one end of the building, a directional antenna suchas a patch or Yagican be used for better penetration of the area.

    Also, for areas that are long and narrow - such as long rows of racking - a directional antennaat one end may provide better coverage. The radiation angle of the antennas will also affect the coverage area.

    ● Point-to-point: When connecting two points together (such as a wireless bridge), the distance, obstructions, and antenna location must be considered. If the antennas can be mounted indoors and the distance is very short (several hundred feet), the standard dipole or mast mount 5.2 dBiomnidirectional may be used. An alternative is to use two patch antennas. For very long distances (1/2 mi. or more), directional high-gainantennas must beused. These antennas should be installed as high as possible, and above obstructions such as trees, buildings, and so on; andif directional antennas are used, they must be aligned so that their main radiated power lobes are directed at each other. With a line-of-site configuration, distances of up to 25 miles at 2.4 GHz and 12 miles at 5 GHz can be reached using parabolic dish antennas, if a clear line-of-site ismaintained. With the use of directional antennas, fewer interference possibilities exist and there is less possibility of causing interference to anyone else.

    ● Point-to-multipoint bridge: In this case (in which a single point is communicating to several remote points), the use of an omnidirectional antenna at the main communication point must be considered. The remote sites can use a directional antenna thatisdirected at the main point antenna.

    Cabling

    As stated above, cabling introduces losses into the system, negating some of the gain an antenna introduces and reducing range of the RF coverage.

    Interconnect Cable

    Attached to all antennas (except the standard dipoles), this cable provides a 50 ohm impedance to the radio and antenna, with a flexible connection between the two items. It has a high loss factor and should not be used except for very short connections (usually less than 10feet). Typical length on all antennas is 36 in. (or 12 in. on some outdoor antennas).

    Low-Loss/Ultra-Low-Loss Cable

    Cisco offers two styles of cables for use with the 2.4-GHz and 5-GHz product lines. These cables provide a much lower loss factor than standard interconnect cable, and they can be used when the antenna must be placed at any distance from the radio device. While these are low-loss cables, they should still be kept to a minimum length.

    There are two types of cable supplied by Cisco for mounting the antenna away from the radio unit. The 100- and 150-foot cables are LMR600 type cable, while the 20- and 50-foot cables are LMR400 type cables. All four lengths are supplied with one RP-TNC plug and one RP-TNC jack connector attached. This allows for connection to the radio unit and to the interconnect cable supplied on the antennas.

    Connectors

    According to the U.S. Federal Code of Regulations, products used in the 2.4- and 5-GHz ISM bandsmanufactured after June 1994 must either use connectors that are unique and nonstandard(meaning not readily available on the market by the average user) or be designed tobe professionally installed (“professional” here indicates a person trained in RF installation and regulations). Since many of the 2.4-GHz products are installed by non-RF trained personnel, these products must comply with the unique connector ruling. The Cisco outdoor access and bridge products are designed for installation by a RF professional, and therefore may use a standard N style connector. Cisco Aironet indoor products use reverse polarity-TNC (RP-TNC) connectors. While they are similar to the normal TNC connectors, they cannot be mated to the standard connectors.

    To ensure compatibility withCisco Aironet products, use antennas and cabling from Cisco.

    Mounting Hardware

    Each antenna requires some type of mounting. The standard dipole antenna simply connects to the RP-TNC connector on theunit. Mast mount antennas are designed to mount to a variety of mast diameters and each comes with mounting hardware for attachment. TheYagi antennas have an articulating mount option. Patch antennas are designed to mount flat against a wall or ceiling, and ceiling-mount antennas are equipped with a drop-ceiling cross-member attachment. The 2.4-GHz 21-dBi parabolic dish mounts to a 1.625- up to a 2.375-in. mast. In this dish antenna, fine-threaded turn-buckles allow accurate aiming of the antenna.

    For most indoor applications, a .75- or 1-in. electrical conduit provides a suitable mounting. For outdoor applications, use a heavy galvanized oraluminum wall mast that will withstand the wind-loading rating of the selected antenna.

    Lightning Arrestors

    When using outdoor antenna installations, it is always possible that an antenna will suffer damagefrom potential charges developing on the antennaand cable, or surges induced from nearby lightning strikes. The Cisco Aironet lightning arrestor is designed to protect 2.4-GHz to 5.8- GHz radio equipment from static electricity and lightning-induced surges that travelon coaxial transmission lines. Both systems need to be properly grounded as identified in the hardware installation manuals of the products. These protection mechanisms will not prevent damage in the event of a direct lightning hit.

    Theory of Operation

    The Cisco Aironet Lightning Arrestor (Figure 5) prevents energy surges from reaching the RF equipment by the shunting effect of the device. Surgesare limited to less than 50 volts, in about .0000001 seconds (100 nanoseconds). A typical lightning surge is about .000002 (2 micro seconds).

    Figure 5. Cisco Aironet Lightning Arrestor

     

    The accepted IEEE transient (surge) suppression is .000008 seconds (8 micro seconds). The Cisco Aironet Lightning Arrestor is a 50-ohm transmission line with agas discharge tube positioned between thecenter conductor and ground. This gas discharge tube changes from an open circuit toa short circuit almost instantaneously in the presence of voltage and energy surges, providing a path to ground for the energy surge.

    Installation

    This arrestor is designed to be installed between your antenna cable and the Cisco Aironet access point. Installation should be indoors, or insidea protected area. A good ground must be attached to the arrestor. This can be accomplished by attaching a ground lug to the arrestor andusing a heavy wire (number 6 solid copper) to connect the lug to a good earth ground (see Figure 6).

    Understanding RF Power Values

    Radio frequency (RF) signals are subject to various losses and gains as they pass from transmitter through cable to antenna, through air (orsolid obstruction), to receiving antenna, cable, and receiving radio. With the exception of solid obstructions, most of these figures and factors are known and can be used in the design process to determine whether an RF system such as a WLAN will work.

    Decibels

    The decibel (dB) scale is a logarithmic scale used to denote the ratio of one power value to another. For example:

    X1`dB = 10 log10 (Power A/Power B)

    An increase of 3 dB indicates a doubling (2x) of power. An increase of 6 dB indicates a quadrupling (4x) of power. Conversely, a decrease of 3 dB reduces power by one half, and a decrease of 6 dB results in a one fourth of the power. Some examples are shown below in Table 1.

    Table 1. Decibel Values and Corresponding Factors

    Increase

    Factor

    Decrease

    Factor

    0 dB

    1 x (same)

    0 dB

    1 x (same)

    1 dB

    1.25 x

    -1 dB

    0.8 x

    3 dB

    2 x

    -3 dB

    0.5 x

    6 dB

    4 x

    -6 dB

    0.25 x

    10 dB

    10 x

    -10 dB

    0.10 x

    12 dB

    16 x

    -12 dB

    0.06 x

    20 dB

    100 x

    -20 dB

    0.01 x

    30 dB

    1000 x

    -30 dB

    0.001 x

    40 dB

    10,000 x

    -40 dB

    0.0001 x

    Power Ratings

    WLAN equipment is usually specified in decibels compared to known values. Transmit Power and Receive Sensitivity are specified in “dBm,” where“m” means 1 milliwatt (mW). So, 0 dBm is equal to 1 mW; 3 dBm is equal to 2 mW; 6 dBm is equal to 4 mW, and so on, as shown in Table 2.

    Table 2. Common mW Values to dBm Values

    dBm

    mW

    dBm

    mW

    0 dBm

    1 mW

    0 dBm

    1 mW

    1 dBm

    1.25 mW

    -1 dBm

    0.8 mW

    3 dBm

    2 mW

    -3 dBm

    0.5 mW

    6 dBm

    4 mW

    -6 dBm

    0.25 mW

    7 dBm

    5 mW

    -7 dBm

    0.20 mW

    10 dBm

    10 mW

    -10 dBm

    0.10 mW

    12 dBm

    16 mW

    -12 dBm

    0.06 mW

    13 dBm

    20 mW

    -13 dBm

    0.05 mW

    15 dBm

    32 mW

    -15 dBm

    0.03 mW

    17 dBm

    50 mW

    -17 dBm

    0.02 mw

    20 dBm

    100 mW

    -20 dBm

    0.01 mW

    30 dBm

    1000 mW (1 W)

    -30 dBm

    0.001 mW

    40 dBm

    10,000 mW (10 W)

    -40 dBm

    0.0001 mW

    Outdoor Range

    The range of a wireless link is dependent upon the maximum allowable path loss. For outdoor links, this is a straightforward calculation as long as there is clear line of sight between the two antennas with sufficient clearance for the Fresnel zone. For line of sight, you should be able to visibly see the remote locations antenna from the main site. (Longer distances may require the use of binoculars). There should be no obstructions between the antennas themselves. This includes trees, buildings, hills, and so on.

    As the distance extends beyond six miles, the curve of the earth (commonly called earth bulge) affects installation, requiring antennas to be placed athigher elevations.

    Fresnel Zone

    Fresnel zone is an elliptical area immediately surrounding the visual path. It varies depending on the length of the signal path and the frequency ofthe signal. The Fresnel zone can be calculated, and it must be taken into account when designing a wireless link (Figure 6).

    Figure 6. Fresnel Zone

     

    Based on both line-of-sight and Fresnel zone requirements, Table 3 provides a guideline on height requirements for 2.4-GHz antennas as various distances. This refers to height above any obstacles located in the middle of the RF path.

    Table 3. Guideline on Height Requirements for 2.4-GHz Antennas

    Wireless Link Distance (miles)

    Approx. Value “F” (60%Fresnel Zone) Ft. at 2.4 GHz

    Approx. Value “C” (Earth Curvature)

    Value “H” (mounting Ht.) Ft. with No Obstructions

    1

    10

    3

    13

    5

    30

    5

    35

    10

    44

    13

    57

    15

    55

    28

    83

    20

    65

    50

    115

    25

    72

    78

    150

    A 10-dB fade margin is included for 2.4-GHz calculations, while the included 5-dB fade margin for5-GHz calculations is sufficient for dependable communications in all weather conditions. Thedistances given are only theoretical and should only be used to determine the feasibility ofaparticular design.

    In outdoor deployments, and as a rule of thumb, every increase of 6 dB will result in a doubling of the distance. Likewise, a 6-dB decrease will halve the distance. Shorter-cable runs and higher-gain antennas can make a significant difference to the range. The following links provide range calculations for the outdoor mesh products:

    ● Cisco Aironet 1550 Series: http://www.cisco.com/c/en/us/support/wireless/aironet-1550-series/products-implementation-design-guides-list.html

    ● Cisco Aironet 1530 Series: http://www.cisco.com/c/en/us/support/wireless/aironet-1530-series/products-implementation-design-guides-list.html

    Regulations

    North America

    Connectors

    In 1985, the FCC enacted standards for the commercial use of spread-spectrum technology in the ISM frequency bands. Spreadspectrum is currently allowed in the 900-, 2400-, and 5200- MHz bands.

    In 1989, the FCC drafted an amendment governing spread-spectrumsystems in the unlicensed ISM band, and Congress enacted this amendment into law in 1990. This amendment is commonly referred to as the “new rules” or “’94 rules” because it impacts all spread-spectrum products manufactured after June 23, 1994. Products manufactured before June 23, 1994, are not affected by the amendment.

    The FCC 1994 rules are intended to discourage use of amplifiers, high-gain antennas, or other means ofsignificantly increasing RF radiation. The rules are further intended to discourage “home brew” systems that are installed by inexperienced users and that - either accidentally or intentionally - donot comply with FCC regulations for use in the ISM band.

    Both the original rules and the amendments sought toenable multipleRF networks to “coexist” with minimum impact on one another by exploiting properties of spread-spectrumtechnology. Fundamentally, the FCC 1994 rules intend to limit RF communications in the ISM band to a well-defined region, while ensuring multiple systems can operate with minimum impact on one another. These two needs are addressed by limiting the type and gain of antennas used with a given system, and by requiring a greater degree of RF energy “spreading.”

    Antenna Gain and Power Output

    FCC regulations specify maximum power output andantenna gain. For the UNII3 band, the FCC limits the transmitter power to 1 watt or 30 dBm, and the antenna gain of an omnidirectional antenna to 6 dBi. For directional antennas operating in a point-to-point system, gains of up to 23 dBi are permitted. For antennas with gain higher than 23 dBi, the transmitter output power must be reduced 1 dB for every 1 dB above 23 dBi increase in the antenna gain.

    At 2.4 GHz, the maximum transmitter power is also 1 watt. Using this maximum power, the maximum antenna gain is 6 dBi. However, the regulations also define the maximum values in regards to the following two different system scenarios.

    Point-to-Point and Point-to-Multipoint Systems

    In point-to-multipoint systems, the FCC has limited the maximum EIRP to 36 dBm. EIRP = TX power + antenna gain. For every dB that the transmitter power is reduced, the antenna may be increased by 1 dB. Thus, 29 dBm TX, +7 dB antenna = 36 dBm EIRP; 28 dBm TX +8 dB antenna = 36 dBm EIRP.

    In point-to-point systems for 2.4-GHz systems using directional antennas, the rules have changed. Because a high-gain antenna has a narrow beamwidth, the likelihood is great that it will cause interference to other area users. Under the rule change, for every dB the transmitter is reduced below 30 dBm, the antenna may be increased from the initial 6 dBi, by 3 dB. Thus, a 29-dB transmitter means 9-dBi antenna; a 28-dB transmitter means 12-dBi antenna. Because we are operating at 20 dBm, which is 10 dB below the 30 dBm level, we can increase the antenna gain by 30 dB. NotethatCisco has never tested, and therefore has not certified, any antenna with gain greater than 21 dBi.

    The main issue that comes up here is: What differentiates a point-to-point from a multipoint system.

    In Figure 7, point A communicates to a single point (point B), and point B communicates to a single point A; therefore, it is simple to see that both locations see this as a point-to-point installation.

    In Figure 8, point A communicates to more than one (or multiple) points; therefore, point A is operating in a multipoint configuration, and the largest antenna permitted is 16 dBi. Point B or point C can each communicate to only one point (point A); therefore, point B andpoint C actually operate in a single-point or point-to-point operation, and a larger antenna may be used.

    Figure 7. Point-to-Point Wireless Bridge Solution

     

    Figure 8. Point-to-Multipoint Wireless Bridge Solution

     

    Amplifiers

    In the FCC rules, Section 15.204-Part C states: “External radio frequency power amplifiers shall not be marketed as separate products.” Part D states: “Only the antenna with which an intentional radiator (transmitter) is originally authorized may be used with the intentional radiator." This means that unless the amplifier manufacturer submits the amplifier for testing with the radio and antenna, it cannot besold in the United States. If it has been certified, it must be marketed and sold as a complete system, including transmitter, antenna, and coaxial cable. Italsomust be installed exactly this way.

    If you are using a system that includes an amplifier, remember that these rules concerning power are still in effect. If the amplifier is one-half (.5) watt (27dBm), this means in a multipoint system, the maximum antenna gain is only 9 dBi, and in a point-to-point system it is only 15dBi.

    ETSI

    The European Telecommunication Standardization Institute (ETSI) has developed standards thathave been adopted by many European countries aswell as many others. Under the ETSI regulations, the power output and EIRP regulations are much different than in the United States.

    Antenna Gain and Power Output

    The ETSI regulations specify maximum EIRP as 20dBm. Since this includes antenna gain, this limits theantennas that can be used with atransmitter. To use a larger antenna, the transmitter power must be reduced so that the overall gain of the transmitter, plus the antenna gain, less any losses in coax, is equal to or less than +20 dBm. This drastically reduces the overall distance an outdoor link can operate.

    Amplifiers

    Since the ETSI regulation has such a low EIRP, the use of amplifiers is typically not permitted in any ETSI system.

    Frequencies and Channel Sets

    IEEE 802.11b/g Direct Sequence Channels

    Fourteen channels are defined in the IEEE 802.11b/g direct-sequence channel set. Each direct-sequencechannel as transmitted is 22 MHz wide; however, thechannel center separation is only 5 MHz. Thisleads to channel overlap such that signals from neighboring channels can interfere with each other. In a14-channel direct-sequence system (11 usable in the United States), only three nonoverlapping (and hence, noninterfering) channels, 25 MHz apart, are possible (forexample, channels 1, 6, and 11).

    This channel spacing governs the use and allocation of channels in a multiple-access-point environment such as an office or campus. Access points areusually deployed in “cellular” fashionwithin an enterprise, where adjacent access points are allocated nonoverlapping channels. Alternatively, access points can be collocated using channels 1, 6, and 11 to deliver 33 Mbps bandwidth to a single area (but only 11 Mbps to a single client). Thechannel allocation scheme is illustrated in Figure 9, and the available channels in the different regulatory domains are defined in Table 4.

    Figure 9. IEEE 802.11b/g DSSS Channel Allocations

     

    Table 4 shows the channels permitted in the corresponding approval areas.

    Table 4. DSSS PHY Frequency Channel Plan

    Channel ID

    Frequency (MHz)

    Regulatory Domains (Maximum Conducted Average Power Levels in dBm)

     

    -A

    -C

    -E

    -I

    -J

    -K

    -N

    -P

    -S

    -T

     

    2400-2484 MHz

     

    Mode

    B

    G

    B

    G

    B

    G

    B

    G

    B

    G

    B

    G

    B

    G

    B

    G

    B

    G

    B

    G

    1

    2412

    X

    X

    X

    X

    X

    X

       

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    2

    2417

    X

    X

    X

    X

    X

    X

       

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    3

    2422

    X

    X

    X

    X

    X

    X

       

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    4

    2427

    X

    X

    X

    X

    X

    X

       

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    5

    2432

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    17

    X

    X

    X

    X

    X

    X

    6

    2437

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    7

    2442

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    8

    2447

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    9

    2452

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    17

    10

    2457

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    11

    2462

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

    12

    2467

       

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

       

    X

    X

    X

    X

       

    13

    2472

       

    X

    X

    X

    X

    X

    X

    X

    X

    X

    X

       

    X

    X

    X

    X

       

    14

    2484

                   

    X

             

    X

             
                                                 

    IEEE 802.11a Channels

    The 802.11a specification today specifies four channels for the UNII1 band, four channels for the UNII2 band, and four channels for the UNII3 band. These channels are spaced at 20 MHz apart and are considered noninterfering; however, they do have a slight overlap in frequency spectrum. It is possible to use adjacent channels in adjacent cell coverage, but it is recommended when possible to separate adjacent cell channels by at least 1 channel.

    Figure 10 shows the channel scheme for the 802.11 bands, and Table 5 lists the North American frequency allocations.

    Figure 10. 802.11a Channel Allocation

     

    Table 5. 802.11a Frequency Plan

    Regulatory Domain

    Frequency Band

    Channel Number

    Centre Frequencies

    USA

    ● UNII lower band
    ● 5.15-5.25 GHz
    ● 36
    ● 40
    ● 44
    ● 48
    ● 5.180 GHz
    ● 5.200 GHz
    ● 5.220 GHz
    ● 5.240 GHz

    USA

    ● UNII middle + extended
    ● 5.25-5.700 GHz
    ● 52
    ● 56
    ● 60
    ● 64
    ● 100
    ● 104
    ● 108
    ● 112
    ● 116
    ● 120 *
    ● 124 *
    ● 128 *
    ● 132
    ● 136
    ● 140
    ● 5.260 GHz
    ● 5.280 GHz
    ● 5.300 GHz
    ● 5.320 GHz

    Additional Information

    SKU AIR-ANT2566P4WR-RF
    Weight (Kg) 1
    Datasheet URL http://www.cisco.com/c/en/us/products/collateral/wireless/aironet-antennas-accessories/product_data_sheet09186a008008883b.html
    Condition Refresh
    Module Type Accessories

    AIR-ANT2566P4WR-RF

    AED

    AED 0

    0