The fickle radio reception in DeKalb may be the result of more than just being on the fringe of Chicago radio’s transmitting range.

Sound clarity, which for many drivers will flicker in and out as their autos amble across town, can be the result of many factors. Between the radio model in the car, stoplights acting as inadvertent antennae and a global phenomenon known as tropospheric scatter, receivers can be victim of a number of interferences.

Dr. Robert Miller, associate professor of media studies, explained the reasoning behind the weak reception of Chicago stations as a line-of-sight issue.

“FM travels on line of sight, and as you get farther from transmitter, the line of the signal is going over your head because of the curvature of the Earth,” Miller said.

The signal’s bottom, the part received this far from the city, is not only weaker, but more susceptible to terrestrial interference, such as trees and buildings, said Miller.

“We are at the edge of Chicago market radio range for certain,” said Jeff Glass, chief engineer of Northern Public Radio. The issues don’t end there.

When stopped at a red light and a song cuts out, it may be caused by the stoplight posts.

“What’s happening is that the stoplight pole, being made out of metal, is acting as an antenna,” Glass said.

When a signal makes contact with the post, it reradiates out into nearby radios, where it interferes with the original signal. The resulting conflict is called constructive and destructive interference.

Glass likened this to ripples colliding on the surface of a pond, either augmenting each other to form higher peaks, or cancelling each other out. Destructive interference, the latter, is what causes the sound to turn to static when the receiver is near the light post.

Perhaps the most elaborate interference, though, is tropospheric scatter, or troposcatter, which occurs in summer months when the atmosphere’s temperature experiences drastic change.

“This causes stations from hundreds of miles away to be heard in communities that wouldn’t usually hear them,” Glass explained.

“When Mother Nature’s involved, there’s not a hell of a lot we can do except live with it,” Glass said.