# RF Calculators

**VPI Laboratories Calculators**

This equation calculates the RF power density per square centimeter based on an antenna port power measurement, the numeric gain of the antenna, and a distance in centimeters. Typically this is used for RF exposure calculations used in determining whether a product is going to require SAR testing or if the device meets MPE exemption levels.

Used to calculate the RF power density per square centimeter based on an Effective Isotropic Radiated Power (EIRP) measurement and distance in centimeters. This calculator is typically used for RF exposure calculations that will be used in determining if a product requires SAR testing or if the device meets MPE exemption levels.

Calculate antenna numeric gain from dBi or numeric. This shows the conversion between a dBi or a numeric gain when needing to know one or the other. Some equations need the gain numeric form (such as the Power Density (Antenna) calculation above) and some need the unit to be in dBi.

Given an EIRP value in Watts and a distance in meters, this conversion calculator gives you an expected field strength. Can be used to ensure a test set up will handle the expected power coming out of a transmitter when given an estimated EIRP.

Passing FCC unintentional and intentional radiated signals testing can sometimes be challenging. VPI Technology's engineers have worked with many different clients to resolve design challenges that stop products from passing FCC testing. Our engineers do not conduct the FCC testing, so you can be assured that there will not be a conflict of interest between our Engineering division and Laboratories division.

Contact VPI's Engineering group today for help with your design and engineering challenges. Call 801-495-2310 or fill out our contact form.

Calculate EIRP or Effective Radiated Power (ERP) in different units from a field strength measurement and a distance in meters. Used to make sure transmitter testing is performing as expected.

The equation converts units from dBm to mW. Typically only used to get one unit converted to the other unit for use in another equation.

The equation converts units from dBuV to uV. Typically only used to get one unit converted to the other unit for use in another equation.

Used to calculate factor for adjusting limits or field strengths for frequencies below 30 MHz (40 dB/decade). The FCC rules allow for a roll off of 40 dB per decade. This equation is used to calculate a correction factor to be applied to a measurement to adjust for distance. Some limits are specified at 300 meters, some at 30 meters, and some at 3 meters. VPI Laboratories is not able to measure at 300 meters, so a correction factor is needed to apply to the measurement to compare the emission to the limit. Two distances are needed for the factor to be calculated. The equation can also be used for determining how fast a frequency rolls off for use as a correction factor.

Used to calculate factor for adjusting limits or field strengths for frequencies above 30 MHz (20 dB/decade)

Calculates a value when the limit changes with the logarithm of the frequency. This equation is used when a standard specifies a limit at one frequency and another limit at another frequency and states that the limit between is a linear interpolation of the log of the frequency. This is usedd when a new standard is brought out or to manually calculate a limit.

Calculates antenna gain from field strength, power to antenna, and distance. This equation will determine the gain using field strength measurements, power at the antenna port measurements, and a distance when the manufacturer does not specify a gain. Typically used for trace antennas. Care must be taken to eliminate any ground plane reflections in the field strength measurements for the calculation to be accurate. Provides both numeric gain and gain in dBi.