Collision response
Field strength in free space is a term in telecommunications. It is the field strength caused by a half wave dipole under ideal conditions. The actual field strength in terrestrial environments is calculated by empirical formulas based on this field strength.
Power density
Let N be the effective power radiated from an isotropic antenna and p be the power density at a distance d from this source[1]
Power density is also defined in terms of electrical field strength;
Let E be the electrical field and R be the impedance of the free space
The following relation is obtained by equating the two,
or by rearranging the terms
Numerical values
Since a half wave dipole is used, its gain over an isotropic antenna ( ) should also be taken into consideration,
In this equation SI units are used.
Expressing the same equation in:
- kW instead of W in power,
- km instead of m in distance and
- mV/m instead of V/m
is equivalent to multiplying the expression on the right by .[2] In this case,