![]() ![]() Typically the device loses about 0.020 dB per foot in an outdoor or wide open office doors, walls, glass, and etc. It is a measure of how much signal power the device loses over a given distance. Free Space Path Lossįree space path loss is a weakening of the RF signal due to a broadening of the wave front. How to find EIRPįor example we have a Cisco 1242AG access points running at full power with a 6dBi antenna on the 802.11a radio and a 2.5dBi antenna on the 802.11bg radio.Ĩ02.11a EIRP = 17dBm (40mw) - 0dB + 6dBi = 23dBm = 200mw of actual output powerĨ02.11bg EIRP = 20dBm (100mw) - 0dB + 2.5dBi = 22.5dBm = 150mw (approx) of actual output powerīased on the example above, in theory, if you were to measure it right at the antenna you could get an RSSI of -23dBm or -22.5dBm respectively. Reference is the reference power (for example, 1 mW). Signal is the power of the signal (for example, 50 mW). This list defines the terms in the formula: Power (in dB) = 10 * log10 (Signal/Reference) ![]() You can calculate the power in dBs from this formula: The abbreviation dB is often combined with other abbreviations in order to represent the values that are compared. The dB measures the power of a signal as a function of its ratio to another standardized value. EIRP (Effective Isotropic Radiated Power)ĮIRP (Effective Isotropic Radiated Power) is the actual amount of signal leaving the antenna and is a value measured in db and is based on 3 values: Other important terminologies that we need to understand is the EIRP and Free Space Path Loss. ![]() 55dBm + -95dBm = 40db this means you have an SNR of 40, the general rule of thumb is that any SNR above 20 is good. For example, lets say your Signal value is -55dBm and your Noise value is -95dBm. To calculate the SNR value, we add the Signal Value to the Noise Value and it generates (or should) a positive number that is expressed in decibels (db). Typical environments range between -90dBm and -98dBm. Looking at this value, if the value is closer to -120 (minus 120) it is better because that means there is little to no interference. Noise level is the amount of interference in your wireless signal, so lower is better. This value is measured in decibels from 0 (zero) to -120 (minus 120). Noise can be due to other wireless devices such as cordless phones, microwave devices etc. Noise is any signal that interferes with your signal. The Signal is also affected by the APs transmit power & antenna as well as the client's antenna. Normal range in a network would be -45dBm to -87dBm depending on power levels and design. Typically voice networks require a -65dBm or better signal level while a data network needs -80dBm or better. The closer this value to 0 (zero), stronger the signal. It is the strength that one device is hearing another device. RSSI (Received Signal Strength Indicator) is a more common name for the Signal value. Let's look at the components of the SNR and then understand how SNR is determined. SNR is measured as a positive value between 0dB and 120dB and the closer the value is to 120dB, the better. In simple words, SNR (Signal-to-Noise Ratio) is a ratio based value that evaluates your signal based on the noise being seen. It is the ratio of signal power to the noise power corrupting the signal. The power level of the RF signal relative to the power level of the noise floor is known as the Signal-to-Noise ratio or SNR. SNR, RSSI, EIRP and Free Space Path Loss Signal to Noise Ratio EIRP (Effective Isotropic Radiated Power). ![]()
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