Weather band radio having digital frequency control

#Weather band radios enable a user to tune into National Oceanic and Atmospheric Administration (NOAA) weather radio (NWR) communications. In the United States, regions have one or more weather radio stations that provide continuous radio broadcasting of weather conditions. This can be especially useful in case of weather-related or other emergency scenarios.

#The weather broadcasting occurs in a relatively narrow bandwidth of the radio frequency (RF) spectrum. Specifically, a total of 175 kilohertz (kHz) bandwidth is available at between 160.4 Megahertz (MHz)-160.55 MHz, allowing a minimal 25 kHz for each channel. This narrowband operation can complicate radio design. In contrast, frequency modulation (FM) radio allows for much wider bandwidth for each channel, allowing much greater headroom for design of an FM receiver.

#Currently available weather radios have been developed using analog radio technology which, although technically feasible, can be expensive to build, is not readily miniaturized to a small form factor, and has relatively minimal programmable capabilities.

#FIG. 1 is a block diagram of a NWR message code format in which communications occur.

#FIG. 2 is a block diagram of a weather band radio receiver in accordance with an embodiment of the present invention.

#FIG. 3 is a more detailed view of a portion of a demodulator and feedback loop in accordance with one embodiment of the present invention.

#In various embodiments, a weather band radio receiver may be provided using a digital signal processor (DSP) to handle demodulation and related functions. In this way, an entire weather band radio receiver can be implemented on a single semiconductor die, including both analog and digital circuitry. In doing so, however, certain complexities may exist, including the potential for generating audible noise while performing automatic frequency control (AFC) in the analog portion. Thus embodiments may further provide an ability to compensate for such noise to reduce or prevent audible artifacts.

#Before discussing a detailed implementation of one such radio receiver, a background of the weather radio spectrum and message code format is in order. As described above, weather radio exists at a relatively narrow bandwidth. Currently, in the United States this bandwidth of approximately 175 kHz provides for the presence of up to seven channels each having a 25 kHz bandwidth. The RF carrier modulation for radio communications is narrowband FM with +/−5 kHz maximum deviation. In turn, the sub-carrier modulation of the message information uses audio frequency shift keying (AFSK).

#Referring now to FIG. 1, shown is a block diagram of a NWR message code format. As shown in FIG. 1, message 10 includes an AFSK digital message 15, which may correspond to a specific area message encoding (SAME) message having a maximum of 268 bytes. In various embodiments, three identical digital messages may be provided in a burst communication, each of which includes the same data repeated three times. Thus this digital message 15 may be demodulated and then further processed to generate a text message suitable for display on a display of a radio or an associated display, e.g., of a video device. The SAME message is phase continuous at bit boundaries, and is transmitted at a bit rate of 520.83 bits per second. Logic zero information is represented at a frequency of 1562.5 Hertz (Hz), while logic one information is represented at a frequency of 2083.3 Hz. The message may have a frequency deviation of between approximately +/−4 kHz to +/−5 kHz. Note that because there is no error control/parity or stop and start bits, the message information is transmitted three times in a row.