About Our Listening Range

A radio station's reach is dependant on a number of factors, including terrain, weather, and other radio stations on or near the same frequency. (Learn more by scrolling down this page.)

Why do AM Radio Frequencies travel farther?

Low frequencies travel farther mostly because they propagate along the surface of the earth. High frequency FM signals are basically line of sight. Under the right conditions, AM signals will bounce off of the ionosphere and can travel around the globe.

Why do FM Radio Frequencies sound better?

FM and AM manipulate radio waves in different ways (frequency versus amplitude) to encode the sound being transmitted. Ultimately, though, each station on FM radio has six times the bandwidth as AM. More bandwidth means more nuanced sounds are possible. Think of it like drawing with 48 colors versus only 8 colors.

Want to get really geeky on the details? Visit this Wikipedia page.

KJIM-AM Radio coverage map


KJIM-FM Signal Coverage


These maps are cool, how are they drawn?

These maps are drawn using engineering data from the FCC. The coverage pattern for each FM station is calculated using the effective radiated power (ERP) of the station and the antenna height above average terrain (HAAT). The HAAT is calculated in all directions based upon the average ground elevation between 1.5 and 10 miles from the station in each direction.

The coverage pattern for each AM station is based on the station's transmitter power, it's field strength pattern, the frequency of the station, and the ground conductivity of the local area.

What do the red, purple, and blue lines mean?

The red, purple, and blue lines correspond to the "local", "distant", and "fringe" predicted coverage areas of each radio station:

  • Local Coverage: Within this area, you should be able to receive the radio station on almost any radio with moderately good to very good reception.
  • Distant Coverage: Within this area, the signal of the radio station may be weak unless you have a good car radio or a good stereo with a good antenna. You may not be able to receive the station at all on inexpensive radios or radios with poor antennas.
  • Fringe Coverage: Within this area, the station's signal will be very weak. You may be able to receive this station if you have a very good radio with a good antenna, but it's possible that interference from other stations may prevent you from picking up these stations at all.

What criteria is used to define the "local", "distant" and "fringe" coverage areas?

The "local""distant" and "fringe" lines on the FM maps correspond to the predicted 60, 50, and 40 dBμ signal strength contours respectively.

The "local""distant" and "fringe" lines on the AM maps corresponds to the predicted 2.0, 0.5, and 0.15 mV/m contours respectively (of the groundwave propogation signal).