Coaxial cable is normally used to connect a radio transceiver to an antenna. Each coaxial cable is designed for specific impedance. In WiFi equipment as well as most radios, we normally used 50-ohm impedance coaxial cable. Fail to meet the impedance will reflect the radio signal from the transmitter back into the transmitter rather than to the antenna. Thus, the impedance of the transmitter, the coaxial cable and the antenna must match to 50 ohm.
Unfortunately, the use of coaxial cable introduces signal loss before it reaches the antenna or vice versa the receiver. Shown in the table is the cable loss at 2.4 GHz for several type of coaxial cable.
Cable Type Loss / 10 meters(on 2.4GHz).
* RG 8 3.3 dB
* LMR 400 2.2 dB
* Heliax 3/8” 1.76 dB
* LMR 600 1.7 dB
* Heliax ½” 1.2 dB
* Heliax 5/8” 0.71 dB
The field experience shows that it would be best if one uses at least LMR coaxial cable. For those who are fortunate enough may use the high performance heliax coaxial cable. It is quite expensive for most of us in developing countries to buy such cable as it costs in the range of US$ 25 / meter. Black market price of heliax cable would be around US$3-4/meter. We normally find heliax coaxial cable from a used or unused cut heliax coaxial cable from a telecommunication project. If it is possible, do not use RG-8 coaxial cable for the installation.
Some of us normally restrict the length of coaxial cable to less then one (1) meter. Consequently, we must put the Access Point or other WiFi equipment up on the tower. The UTP Local Area Network (LAN) cable then run down from the top of the tower to the Network Operating Center (NOC) located at the bottom of the tower. Environment enclosure should be used to protect the WiFi equipment located on top of the tower.
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