Most frequencies above 30 MHz are assigned on a local basis. To know where to listen for your local police or fire department, you'll need a frequency guide or directory for your locality. However, some frequencies, particularly those used for emergency or inter-agency communications, have been allocated nationally. The following is a list of some of the more widely used and active national frequencies.

34.90: This channel is used nationwide by the National Guard during emergencies.

39.46: Used for inter-department emergency communications by local and state police forces.

47.42: This is a channel used across the United States by the Red Cross for relief operations.

52.525: This is a calling frequency used by ham radio operators in FM on their six-meter band. During periods of exceptional propagation, this frequency is filled with signals from hundreds or even thousands of miles away. If you're hearing distant signals here, then the 30 to 50 MHz range is also open for long distance reception.

121.50: This is the international aeronautical emergency frequency.

138.225: This is the prime disaster relief operations channel used by the Federal Emergency Management Agency; it is active during earthquakes, hurricanes, floods, and other catastrophic events.

146.52: This frequency is used by ham radio operators for non-repeater communications on the two-meter band; it is very busy in many parts of the country.

151.625: This channel is used by "itinerant" businesses, or those that travel about the country. Circuses, exhibitions, trade shows, and sports teams are some of the users you can hear. Other widely used itinerant channels are 154.57 and 154.60.

154.28: Used for inter-department emergency communications by local fire departments; 154.265 and 154.295 also used.

155.160: Used for inter-department emergency communications by local and state agencies during search and rescue operations.

155.475: Used for inter-department emergency communications by local and state police forces.

156.75: This channel is used internationally for broadcasts of maritime weather alerts.

156.80: This is the international maritime distress, calling, and safety channel. All ships must monitor this frequency while at sea. It is also heavily used on rivers, lakes, etc.

162.40: This channel is used for NOAA weather broadcasts and bulletins.

162.425: This channel is used for NOAA weather broadcasts and bulletins.

162.45: This channel is used for NOAA weather broadcasts and bulletins.

162.475: This channel is used for NOAA weather broadcasts and bulletins.

162.50: This channel is used for NOAA weather broadcasts and bulletins.

162.525: This channel is used for NOAA weather broadcasts and bulletins.

162.55: This channel is used for NOAA weather broadcasts and bulletins.

163.275: This channel is used for NOAA weather broadcasts and bulletins.

163.4875: This channel is used nationwide by the National Guard during emergencies.

163.5125: This is the national disaster preparedness frequency used jointly by the armed forces.

164.50: This is the national communications channel for the Department of Housing and Urban Development.

168.55: This is the national channel used by civilian agencies of the federal government for communications during emergencies and disasters.

243.00: This channel is used during military aviation emergencies.

259.70: This channel is used by the Space Shuttle during re-entry and landing.

296.80: This channel is used by the Space Shuttle during re-entry and landing.

311.00: This is an active in-flight channel used by the U.S. Air Force.

317.70: This is an active channel used by U.S. Coast Guard aviation.

317.80: This is an active channel used by U.S. Coast Guard aviation.

319.40: This is an active in-flight channel used by the U.S. Air Force.

340.20: This is an active channel used by U.S. Navy aviators.

409.20: This is the national communications channel for the Interstate Commerce Commission.

409.625: This is the national communications channel for the Department of State.

462.675: This channel is used for emergency communications and traveler assistance in the General Mobile Radio Service.