Measuring Part 15 FM Field Strength

[R. Fry]

Posts on another board asked how a Part 15 hobbyist could measure field strength from a Part 15 FM transmit antenna, and how to set the right length of the whip antenna used on a field strength meter.  Following is my reply, FWIW:A field intensity meter designed to measure radiated fields with the accuracy needed for Part 15 certification will have its own antenna, and that cannot be modified without destroying the calibration of that meter. It will also have a means of determining that field intensity in standard units, such as millivolts/meter (mV/m), or microvolts/meter (µV/m).Another type of field strength meter is designed for the cable industry, and gives readings calibrated in terms of decibels with respect to 1 µV (dBµV) in a 75 ohm coaxial cable environment. A user can feed that meter with a receiving antenna, and the meter may read something -- but it can't measure radiated fields accurately, because that system has not been designed and calibrated to do so.The more common types of "field intensity meters" only show relative values, and can't be used to prove Part 15 compliance.//