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The radio link range is one of the most important aspects in a UAV. How far can we go with a good radio link? What affects this distance? How to increase the link range? are usual questions that concerns to UAV developers and manufacturers. Well this are the main factors that will have influence while achieving the maximum possible distance: - Bandwidth: the rate of data transfer, bit rate or throughput, measured in bits per second (bit/s). - Transmitter power: is the actual amount of power (in watts) of radio frequency (RF) energy that a transmitter produces at its output. - Antenna gain: an antenna's power gain or simply gain is a key performance number which combines the antenna's directivity and electrical efficiency. Normally the higher the gain, the narrowest radiation patter, f.e. a omny antenna has typically 3 to 5 dBis while a patch antenna can have 9 to 18 dBi but the patch antenna like the used in the G-TRACK must be always aiming to the UAV to have good link quality. - Losses: connectors and cables reduces the final output power of the system as it has looses. - Receiver sensitivity: Is the minimum magnitud of input signal required for a good performance of the device. - Fade Margin: Is the minimum margin necessary to ensure a good communication link measured in dBi a desired fade margin is 20 dB. - Path Loss: The losses produced by the attenuation of the signal caused by the distance between the two radios. - System Gain: Final system transmiting power taking into consideration all the installation; is the sume of the following: Transmitter Power + (Transmitter Antenna Gain - Transmitter Cable and Connector Losses) + (Receiver Antenna Gain - Receiver Cable and Connector Losses) + | Receiver Sensitivity | The following example shows an estimation fo the distance that you can achieve using the PCM data link with both ground and air omny antennas: Tx power = 30dBm (equivalent to 1W) Tx antenna gain = 6dBi Tx cable/connector loss = 2dB (typical value for one meter coax cable) Rx antenna gain = 3dBi Rx cable/connector loss = 2dB Rx sensitivity = -108dBm System Gain = [30+(6-2)+(3-2)+108]dB = [30+4+1+108]dB = 143dB. Under this situation we can have maximum path loss of (System gain - Fade Margin) 143 - 20 = 123 dB that in the frequency of 2.4 Ghz is equivalent to 15 Km. A table that shows some Path Loss values can be found below. Distance (Km) Master Height (M) Remote Height (M) Path Loss (dB) 5 15 2.5 116.5 5 30 2.5 110.9 8 15 2.5 124.1 8 15 5 117.7 8 15 10 105 16 15 2.5 135.3 16 15 5 128.9 16 15 10 116.2 16 30 10 109.6 16 30 5 122.4 16 30 2.5 128.8
