Short Wave Radio: 1 2
Modulation is the process by which intelligence (voice, music etc.) is added to radio waves produced by a transmitter. The different methods of producing a radio signal are called modes. A radio signal is known as a carrier. The sound you hear between songs or announcements on a radio station, known as dead air, is actually the carrier. While there is no intelligence in a dead carrier, you can tell its being transmitted by how it quiets the background noise on your radio.
Single Sideband (SSB)
SSB is a much more efficient mode than AM since all of the transmitter's power goes into transmitting useful intelligence. A SSB signal also occupies only about half the frequency space of a comparable AM signal. However, SSB transmitters and receivers are far more complicated than those for AM. In fact, a SSB signal cannot be received intelligibly on an AM receiver; the SSB signal will have a badly distorted Charlie Browns mother sound. SSB is used mainly by ham radio operators, military services, maritime and aeronautical radio services, and other situations where skilled operators and quality receiving equipment are common. There have been a few experiments in using SSB for shortwave broadcasting, but AM remains the preferred mode for broadcasting because of its simplicity.
Frequency Modulation (FM)
FM is mainly used on frequency above 30 MHz, where adequate frequency space is available. This is why most scanner radios can only receive FM signals, since most signals found above 30 MHz are FM.
The big advantage of FM is its audio quality and immunity to noise. Most forms of static and electrical noise are naturally AM, and a FM receiver will not respond to AM signals. FM receivers also exhibit a characteristic known as the capture effect. If two or more FM signals are on the same frequency, the FM receiver will respond to the strongest of the signals and ignore the rest. The audio quality of a FM signal increases as its deviation increases, which is why FM broadcast stations use such large deviation.
Below you'll find useful information regarding time such as UTC(Coordinated Universal Time) and the GMT (Greenwich Mean Time) which is still widely used around the world. This will be helpful when trying to find shortwave broadcasts as they will use one or the other of the above mentioned for their broadcast times.
The official US time clock - UTC Time Right now, the official US time is
Greenwich Mean Time (GMT) Greenwich Mean Time (GMT)
Greenwich, England has been the home of Greenwich Mean Time (GMT) since 1884. GMT is sometimes called Greenwich Meridian Time because it is measured from the Greenwich Meridian Line at the Royal Observatory in Greenwich. It is the place from where all time zones are measured.
Day Bands vs. Night Bands
Because shortwave signals depend on such factors as the sun, the ionosphere and interaction with the earth itself, signals cannot be heard on all bands throughout the day. Some bands are best during the daylight hours, and some are best at night. In general, the bands with frequencies below 13 MHz (13000 KHz) are better at night and the bands with frequencies above 13 MHz (13000 KHz) are best during the day.
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