If tough, dried-out roast beef haunts you in your dreams, you know the importance of not overcooking meat. The more beef cooks, the less succulent it becomes; quality declines most quickly past medium, or an internal temperature of 145 degrees Fahrenheit. That's the temperature recommended by the U.S. Department of Agriculture, but for juicy, rare roast beef, you can't cook it that much.
Automatic Packet Reporting System (APRS) is a digital communications system that uses packet radio technology to transmit information and text messages over amateur radio.
Two characteristics, amplitude and frequency (see Fig. 2), mark the difference between AM and FM radio. AM stands for amplitude modulation, which means the amplitude of the radio signal is used to encode information. FM denotes frequency modulation, which uses a change in frequency to encode information. From this you can see that both AM and FM radio use modulation to encode information.