Highly Directional in Software

Creator Data Matrix in Software Highly Directional

Highly directional antennas are generally used for WAN links such as point-topoint or point-to-multipoint The parabolic dish and grid antenna are common examples of these antenna types Using these antennas, you can create a link that spans up to 35 miles With prices under $500 in many cases, creating a single link (two antennas, two wireless bridges, connectors, and mounting kits) can cost less than $1500 Assuming the air is uncongested with RF traffic, this link can be less expensive than the cost of leasing a line for two months If the wireless link provides the needed bandwidth, it is a great cost/benefit solution Figure 4-23 shows an example of a parabolic dish antenna, and Figure 4-24 shows the grid antenna Notice the similarities between the parabolic dish and a satellite dish

FIGURE 4-23

FIGURE 4-24

This form factor allows for less of the signal to propagate behind the antenna and therefore provides more strength in the desired direction of propagation The grid antenna, with the holes in the back panels, withstands heavy winds well and is useful to maintain alignment in high wind areas

You will need more than just an antenna and a wireless device to get your wireless connections working In many cases, connectors, amplifiers, and mounting kits are all needed

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In addition to the different types, there are also variations on each type For example, the N-type connector comes in standard, reverse-polarity, and reverse-threaded models When selecting antennas, connectors should match your equipment When selecting an RF connector, make sure it matches your equipment in type and impedance Look closely at the packaging for the antenna and the device to ensure they both use the same connector type In some cases, adapters are available to convert from one connector type to another, but you must verify that the use of a pigtail adapter does not breach FCC regulations The FCC states that an adapter can be used only if it is part of a certified system While it is not illegal to sell the pigtail adapters, it may be illegal to use them with your equipment This is reminiscent of the old days when crackers would phone phreak the telecom network with tone generators It was legal to buy all the items to build the tone generator at your local electronics store, but if you used them to break into the phone network, you were of course committing a crime If you ve heard of blue boxing, you ve heard of phone phreaking Blue boxing, a kind of phone phreaking, was a method used to access the long-distance mode of the telephone network without paying for it You might think of it as using licensed wireless bands today without paying for them only then someone really paid for the implementation of the infrastructure

RF cables are used to connect the transceiver to the antenna (and possibly other in-series devices) Cables have different levels of loss, and this should be considered when selecting the cabling for your system Keep the following factors in mind when selecting RF cables for your implementation:

Different cables have different levels of loss, so not all cables are the same Make sure the impedance of the cable matches the rest of your system Be sure to select cable that is rated for the frequency you will be using Check with the vendor to discover the loss incurred per foot or per 100 feet

Higher frequencies mean greater loss in the same cable Either master the art of building cables or hire a professional to cut the

Lightning arrestors are installed in order to redirect or shunt electric currents caused by lightning strikes in close proximity They are not meant to protect against direct lightning strikes Sadly, if your antenna is struck directly by lightning, you will lose it and most likely the equipment to which it is attached Lightning arrestors are installed in series between the antenna and the AP or bridge (transceiver) Extra components installed between the lightning arrestor and the antenna, such as connectors or amplifiers, will not be protected by the lightning arrestor For this reason, you should install the lightning arrestor closer to the antenna with nothing between it and the antenna if possible Lightning arrestors should be rated at <8 s Among the features to look for in lightning arrestors are

Meeting the IEEE standard of <8 s Gas tube breakdown voltage Reusability Impedance Frequency response Connector types

The basic functionality of a lightning arrestor is as follows: 1 Lightning strikes near the wireless antenna 2 Transient currents are induced into the antenna or RF transmission line 3 The lightning arrestor senses these currents and immediately causes a short in order to direct the current to earth ground