Field Strength vs. Radiated Power and Distance

Field strength in volt per meter (V/m)
vs. radiated power and distance

The graph shows the proportion between field strength (y-axis), distance (x-axis) and ERP (the curve). The graph illustrates how high the field strength is at a given distance from the antenna when ERP is 1, 10, 25 and 100 watt, respectively. Because antennas are often directional it has to be clear how high the ERP is in the direction required. After this the graph can be used from 1-1000 m away from the antenna. How to use the graph is illustrated below by an example.		SEE ALSO:
		Useful Data main page SWR Nomograph (1+2) SWR including Feeder Loss Mismatch Loss related to SWR Attenuation vs. Frequency Wind Loading Field Strength vs. Radiated Power Conversion tables (1), (2) and (3)

Field Strength in volt per meter vs. Radiated Power and Distance	Example: How high is the field strength 30 m away from the antenna when the radiation of the antenna is 10 watt ERP. 30 metres is found on the x-axis and the readings are made where the yellow graph indicates 10 watt ERP. Readings on the y-axis show 0.75 V/m. The graph can also be used if a field strength of 1 V/m – 20 m away from the antenna is required and where the ERP power to be used is unknown. Here the point is found in the graph - notice that the green line indicating 25 watt passes through this point. As readings indicate in the graph the field strength is very low on 1000 m even at 100 watt ERP. This shows that a high ERP is needed on 1000 m before the field strength becomes important at this distance.