AM radio waves have a unique quality. During the day, the travel around the curvature of the earth in what's called a groundwave. They reach 30 to 50 miles from their source. At night, changes in the ionosphere cause changes in the way AM radio waves travel. That's called the skywave effect and it bounces AM waves between the earth and the upper atmosphere allowing them to travel hundreds of miles.
Interesting, but how does it affect the conversion of an auto salvage operation into a sustainable energy demonstration project?
The proposal includes a wind turbine atop a 79-foot steel tower. Though not a propeller turbine, its tower could interfere with the AM signal generated at nearby WPLM.
"I don't come here tonight to oppose the project," attorney John Woods said, representing the radio station. "I only come here to question it."
He questioned the "detuning" of the tower. WPLM has four antennas not to produce a stronger signal, but to direct it away from two other radio stations' signals at night.
Ed Perry not only owns and operates WATD, he consults with Verizon Wireless on the erection and detuning of its cell phone towers.
"Anything vertical, of a substantial height, reflects radio waves, unless it's detuned," Perry said. "If WPLM is unable to protect those other two stations because it can't direct its signal, it would no longer comply with its FCC license."
The Federal Communications Commission regulates radio stations and cell phone towers. It has no jurisdiction on wind turbines.
"Zoning Boards everywhere generally don't understand this," Perry said. "Its similar when people build big buildings. That's why WMEX had to move its transmitter out of Quincy."
The answer is detuning.
"We do it to cell phone towers all the time," Perry said. "It makes the pole invisible to the AM signal. It's an old technique that been used for years. "
A directional meter determines whether a structure absorbs or reflects a radio signal. Wires precisely placed between the tower and the ground removes the effect.
Sergio Quadros, one of the turbine proponents, concurred.
"This issue is dealt with day to day in Europe and elsewhere," he told the board members at their Wednesday night meeting.
"We need to have time to absorb the intricacies of this project," attorney Wood said. "It's not just a one night affair."
Board members discussed the possible need for peer review. That would mean hiring a consultant of the board's choice and billing the proponents.
The board voted unanimously to continue the hearing until May 18. If the attorneys for both parties don't agree on the required engineering, board chairman Peter Connor will order a peer review.