The calculator converts from radiated power (EIRP) at the output of the transmitter in dBm to the electric field strength* dBµV/m (deciBels micro-volt per meter).
*Electric Field Strength and Electric Field Intensity refer to the same thing
Typically this measurement is made at 3 meters for the purposes of FCC testing. However you can specify any distance in the calculator.
Use this calculator to determine if you will pass the FCC limit test by making a measurement of the transmit power (EIRP) at the RF IN/OUT port of your device.
Let’s say for example you want to certify your receiver product. Here are the steps you would use to find the field strength:
- Connect the RF input port to a spectrum analyzer and make a measurement at a desired frequency.
- Measure the signal power at this frequency (in dBm).
- Next use this calculator to find the EIRP (in dBm) taking the antenna gain into consideration.
- Use the EIRP in the calculator on this page and it will give the Field strength in dBuV/m at any specified distance
For an EIRP of -10 dBm, the field strength at 3 meters is calculated to be 85.2 dBuV/m.
The dBuV/m to dBm tool provides the reverse calculation. For example if the FCC limit is specified to be 55 dBuV/m at a 3m distance, then the maximum EIRP is not to exceed -40.2 dBm.
💡 Note that there is a frequency dependence to this limit (i.e. the field intensity limit will vary with frequency) so the EIRP should be taken account based on this.