Antenna Cable

 < Day Day Up > 



Attached to most antennae (except the standard dipoles), is an interconnect cable. This cable provides a 50 Ohm impedance to the radio and antenna, with a flexible connection between the two items. (As a point of reference, antenna equipment for televisions is 75 Ohm.)

RF cabling has a high loss factor and should not be used except for very short connections. The cable length should have been determined during the site survey. The typical length is three feet, more or less, although it is possible to run an antenna cable as far as 40 feet and still obtain adequate signal strength. However, the reader should understand that the longer the cable, the more signal loss there is, so select the most direct route from the antenna to the radio.

Low loss/ultra low loss cable provides a much lower loss factor than an interconnect cable, and should be used when the antenna must be placed at any distance from the radio device. Also, although the cable is low loss, it should still be kept to a minimum length. Thankfully, many times low loss cabling is the only cable type supplied by vendors (e.g. Cisco) for mounting the antenna away from the radio unit.

Low loss/ultra low loss cable is usually offered in four different lengths with one RTNC plug and one RTNC jack connector attached. This allows for connection to the radio unit and to the interconnect cable supplied on the antennae. While they are similar to the normal TNC connectors, they cannot be mated to the standard connectors.

Note 

If you are not careful you may be tied to one vendor insofar as AP / antennae are concerned. For example, you are installing Cisco Aironet products, to ensure compatibility with the Cisco products, you are required to use antennae and cabling from Cisco.

AP Antennae

The deployment team also must consider how the antennae are to connect to the access point. It is assumed that the access points will be placed in out-of-the-way locations, such as being hidden by ceiling tiles, up high on a beam, over the top of a window, etc. Many times the positioning of the access point isn't conducive to its antenna placement. But when positioning an antenna apart from the access point, keep in mind that antenna cabling can cause signal loss. This is true at both the transmitter and the receiver. As the length of cable increases, so does the amount of loss introduced. To operate at optimum efficiency, keep cable runs as short as possible.

Wireless NIC Antennae

Correctly connecting the radio to a removable antenna will make the system more flexible, and it can increase both the device's range and throughput speed. But many wireless NICs come with the antenna built-in; thus they cannot be removed. Such a card may prevent you from connecting, if your location requires more "gain" to cover the distance. So if any of your end-users need a wireless set-up that provides more gain, look for a PCMCIA card with external antenna connectors. They are identified by a small round connector on the end or side of the card—the connectors are sometimes covered with small plugs, so look carefully.

Antenna Cabling Selection Process

To reiterate, any time you run cable to connect an antenna to its associated device, there will be signal loss. So make your runs as short as possible. To help you in your cabling decision-making, use an attenuation calculator. Times Microwave Systems provides attenuation calculators at its website, http://www.timesmicrowave.com/tele-com/cable_calcultors.

Don't be confused if your equipment has several different types of connectors. There are adapters and pigtail cables available to connect to just about anything.

Once you've tested all the cabling and connectors, you can fasten the cable to form a secure installation. The best way to do this is to use cable clips that fit over the cable and allow you to mount the cable against, for example, a wall for a professional-looking job. These clips are very inexpensive, usually running less than 20 cents each. The clips should be spaced evenly to provide sufficient support. Trusty cable ties (zip ties) can be used to secure the cable to the antenna mast. Right angle "N" connectors also can be used to alleviate stress on your coax cable if the mounting orientation is awkward.

Lightening arrestors, signal splitters / combiners and perhaps even amplifiers (although amplifiers are strictly regulated) may also form part of your RF connection hardware rig.

When selecting antenna cable, the author's best advice:

  • The shorter, the fatter-the better.

  • Plan the location of your radio to minimize the length of antenna cable needed.

  • As the length of your cable increases, compensate by using lower loss (thicker) cable.

  • Connect the antenna directly to the radio to eliminate cables whenever possible.

  • Check with the manufacturer of the WLAN system hardware before adding new cables and connectors!

click to expand
Figure 21.1: A pigtail cable, which is simply a small length of cable with adapting connectors to join a proprietary socket on a device to an external antenna cable.



 < Day Day Up > 



Going Wi-Fi. A Practical Guide to Planning and Building an 802.11 Network
Going Wi-Fi: A Practical Guide to Planning and Building an 802.11 Network
ISBN: 1578203015
EAN: 2147483647
Year: 2003
Pages: 273

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net