Why Does the FCC use Microvolts(µV) to Determine the Power Output (Field Strength) of a FM Transmitter?
Great question, the best source we’ve found to help explain that is at Ramsey Electronics.com. Below is a copy of what they say: The new FCC Part 15 Rules specify a maximum “Field Strength” of your transmitted signal. Since it is unlikely that you have the equipment to carry out accurate field strength measurements in microvolts, it is useful to understand at least the theory of field strength so that you can understand both what you can expect from such transmitters, and what limits the FCC intends. Previous limits on nonlicensed FM-broadcast band devices were defined as a maximum field strength of 40µV per meter measured at a distance of 15 meters. The June 1989 revised rule specifies a maximum of 250 µV per meter, but measured at 3 meters from your antenna. The term, “250µV per meter” means that an accurate field-strength meter with a calibrated and scaled 1-meter antenna may indicate a maximum signal field strength of 250µV (In contrast, non-licensed operation from 26.96 to 27.28 M
