How Radio is Made:

The expected range for an unlicensed, but legal FM broadcast station is not measured in watts, but in signal strength received by a calibrated signal strength meter. Radio Free Burning Man operates under Part 15 of the FCC rules for "intentional radiators." This means that the RFBM can transmit legally as long as it does not exceed 1 microvolt-per-meter, 2450 feet away from the transmitter. The actual wording of the rules states that the signal strength must not exceed 250-microvolts/meter measured three meters away from the antenna. In FM broadcasting, the 1-microvolt/meter measurement is considered to be the outer range of a station. In our case the system is designed to provide the maximum use of its small signal within a 2450-foot radius.

The transmitter used is a Ramsey FM-25b Part-15 unit. The coaxial RF output is coupled to the antenna using 50-feet of Times LMR-400 cable. The antenna, side mounted near the top of the tower, is a home-made Jampro Penetrator. The two antenna bays are fed with a 75-ohm, 3/4-wave, coaxial harness. No vertical beam-tilt is designed into the antenna array.

The Ramsey FM-25b transmitter is fed unbalanced audio from the bypass/test jacks on the back of an Orban Optimod 8000A. This limited and conditioned program audio utilizes the stereo generator in the FM-25b rather than the one in the Optimod. The internal interface between Ramsey's stereo generator and the transmitter's modulation section is superior than any attempt to interface it directly. The FM-25b's stereo generator seems to function better than the Optimod.

The Orban Optimod 8000A dates back to the mid-seventies. This simple broadcast limiter was a breakthrough in FM broadcasting in its day. Since it is much simpler than its successors and imitators, the Optimod provides a more subtle effect on the station sound where the concepts of competitive sound do not apply. This unit averages the program audio from the console, limits the sharp peaks and sibilance that cause annoying distortion, and uses a variable-rate release time to reduce listener fatigue associated with other, simpler limiter circuits.