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.
3. What criteria do you use 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).