From http://www.nws.noaa.gov/nwr
NOAA Weather Radio (NWR) is a nationwide network of radio stations broadcasting continuous weather information direct from a nearby National Weather Service office. NWR broadcasts National Weather Service warnings, watches, forecasts and other hazard information 24 hours a day.
Working with the Federal Communication Commission's (FCC) Emergency Alert System, NWR is an "all hazards" radio network, making it your single source for comprehensive weather and emergency information. NWR also broadcasts warning and post-event information for all types of hazards--both natural (such as earthquakes and volcano activity) and environmental (such as chemical releases or oil spills).
Known as the "Voice of NOAA's National Weather Service," NWR is provided as a public service by the National Oceanic & Atmospheric Administration (NOAA), part of the Department of Commerce. NWR includes more than 850 transmitters, covering all 50 states, adjacent coastal waters, Puerto Rico, the U.S. Virgin Islands, and the U.S. Pacific Territories. NWR requires a special radio receiver or scanner capable of picking up the signal. Broadcasts are found in the public service band at these seven frequencies (MHz):
162.400 162.425 162.450 162.475 162.500 162.525 162.550
Basically, when you purchase a NOAA weather radio receiver, it is pre-programmed to search through these frequencies until it finds the strongest broadcast. You can then use it get the weather information for your area anytime of the day. The cool part is the Weather Alert feature. Your receiver will sit quietly listening to the NWR audio stream, but if there is an emergency, it will sound an alarm and start playing the NWR audio.
A really funny trick to play is to transmit your own NWR alert tone (four seconds of 1050 Hz tone) on the NWR frequency using an out-of-band transmit modified amateur radio transceiver. The Yaesu FT-50 is a good choice. This way, you can set off the NWR receiver - getting everyone's attention - then proceed to broadcast your own weather alert message. Hilarity will definitely ensue.
A good bonus is some public broadcasting or low power FM/TV systems will often play the direct, raw audio following a NWR alert (most stations don't have a 24-hour staff). It's possible to sit outside their transmitter site or office and set off the over-the-air broadcast NWR alert system. You can then inject your own audio commentary into the TV or FM station broadcast.
Below is a schematic for a hardware-based audio tone generator. This should be connected to your radio's microphone input jack, which should be described in the manual. You'll need an audio frequency counter or oscilloscope to tune the output frequency. It doesn't have to be exact. Experiments showed even a 1000 Hz tone would set off some receivers.
