Terrain, antenna heights, foliage, buildings, interference, and antenna gains play a huge role in determining how far a radio can communicate. A 5 watt radio modem transmitting 5 watts of RF can be received thousands of miles away in free-space. ![]() For quick range calculations, assume 6-10dB drop for every doubling of distance.įor example, in the above image, if the center dark-blue circle were 1/2 mile across at -70dBm signal, the -80dBm range would be about 1 mile, the -90dBm circle 2 miles and the -100dBm circle 4 miles across.īut, remember that most all communication systems on earth are limited by terrain not line-of-sight distance. 1/4power is a 6dB drop in RSSI, so when a receiver with a given RSSI moves twice the distance from a transmitter, the RSSI will drop at least 6dB. This is a square-law phenemoena, so the received signal will drop by at least 1/4 every time the distance from the transmitter doubles. Radio Signal Strength (RSSI) will drop the further away a receiver is from the transmitter it is receiving. 1/100th of a mW is -20dBm, 1/1000th of a mW is -30dBm and so on. Everytime the received power drops by 1/10th, the RSSI will drop by 10dB. Every time the received power drops in half, the RSSI will change by 3dB.5mW = -3dBm.25mW = -6dBm and so on. RSSI is usually expressed in dBm which is decibels relative to milliwatts of received power. ![]() Raveon GPS tracking products also include location (latitude/Longitude) with the RSSI information which makes RF propagation analysis very simple. All Raveon data radio modems have a built in RSSI indicator to help determine the signal strength of a received radio modem signal.
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