Legally signal transmit power in antenna dBmW allowed is 36, meaning that if you use a 24dBi parabolic antenna, you may only use WLAN equipment with a power of 15 dBm (about 30 mW only). Generally, existing WLAN equipment on the market have between 15-20 dBm transmit power (30-100 mW). Radiation emitted in antenna usually be measured with Effective Isotropic Radiated Power (EIRP), which is measured in dBm. In their agreement, IndoWLI colleagues seem inclined to agree allowable EIRP is 36dBm. EIRP which is a power in radiasikan at the end of the antenna, can be calculated from: EIRP (dBm) = TX Power - TX Cable Loss + TX Antenna Gain. With the batasinya EIRP of 36dBm, and the average loss in the coax cable & connectors at 5 dB.
So if we use a 21 dBi parabolic antennas, transmit power that can be used only 20 dBm (100 mW). That is, the use of power amplifiers to be very in forbid, you might incur a fine of Rp. 600 million and or imprisonment of 6 years according to article 55 UU36/1999. To determine the System Operating Margin (SOM), we must see Free space loss-FSL, Margin Operating System, Sensitivity receiver (Rx), antenna gain and cable loss. The concept of attempted calculations are shown in the overview above system. Free Space Loss (FSL) is a loss (losses) that occur in communication connections via radio waves can be formulated as follows: FSL = 20 log 10 (Freq, in MHz) + 20 log10 (distance, in miles) + 36.6. From the simple calculation above, then for a distance of 5 km and the frequency of 2400 MHz (2.4 GHz), FSL = 114 dB Furthermore, the need to calculate is the Margin on Operating Systems (System Operating Margin - SOM) for the system to continue to work well. Formula to note is actually very simple which only requires the ability not only added, namely: SOM = Rx signal level - Rx sensitivity. Rx signal level = Tx Power - Tx Cable Loss + Tx Antenna Gain - FSL + Rx Antenna Gain - Rx cable loss. To be safe from radio interference, such as fading, multipath, etc.. the margin of the operating system should be at least 15dB. IEEE 802.11b radio sensitivity in general have a Rx sensitivity = -77 dBm. If we use a dipole antenna, the Tx / Rx antenna gain is 3 dBi. Some colleagues, especially in WARNET many uses parabolic antennas to increase the Tx / Rx antenna gain to 24 dBi. For built-in antenna, the Tx / Rx cable loss = 0 dB. For installations in WARNET that are outside the building, then the Tx / Rx cable loss can reach 5 dB. From the above calculation, for nano-cell with Tx / Rx antenna cable loss 3dB and 0dB, it will be obtained Tx power 14 dBm or 25 mW. Thus the equipment-based 802.11b access point that there are now suitable / appropriate for the needs of nano cell above because most beroutput 25-50 mW. For the purposes of WARNET if counted correctly, then for a distance of 5-7 km we need a IEEE 802.11b equipment at 2.4 GHz with a power around 20 dBm or 100 mW.
For those users WaveRider (http://www.waverider.com) calculation process is simplified by the tool facility in the form of excel file. In the tool we can easily calculate System Operating Margin (SOM), as shown in the picture. We just enter the type of antenna, type of equipment that we use Waverider, antenna length, distance etc then it will appear how SOM, Freshnel Clearence Zone (FZC) etc.. What a coincidence that not only provides a tool for SOM & FZC calculation, but also the calculation to determine the direction and elevation antenna of each node. This is very helpful, if we are equipped with Global Positioning System equipment (GPS) which provides location information (altitude, latitude and longitude), then by including information on the location, direction and elevation antenna antenna can be calculated directly. Other information was also brought by the software is the computation of antenna height, which is based on the calculation of FZC.