Maximum Field Strength Calculator
This calculator calculates the maximum field strength that a dipole antenna could produce at 3M assuming 100% antenna efficiency. This give you an upper bound for transmitter power. The calculator is based on the Maxim app note 3622 which can be found at: www.maxim-ic.com.
The power density for an isotropic antenna at 3m :
PD= Power/Surface Area= Power/4*PI*r2
Volts/meter= sqrt(PD*377) = sqrt(377*Power/(4*PI*r2))
The 377 factor is the resistance of free space in ohms.
Dipole gain in dB compared to an isotropic antenna is 2.15dB
So the gain is 1.281.
Thus the maximum field strength for a dipole is:
It should be noted that the field strength is inversely proportional to distance, so the field strength at 30m is 1/10 the strength at 3m.