Stuart McLachlan
stuart at lexacorp.com.pg
Mon Nov 24 16:05:33 CST 2003
On 24 Nov 2003 at 12:37, Arthur Fuller wrote: > Someone asked me to explain the difference between AM, FM and short wave > and I suddenly realized that I have huge gaps in my alleged knowledge of > same. Can someone point me to a net-splanation or supply one? > AM = Amplitude modulation. The signal is on a set frequency and the information in encoded by varying the strength of it (the amplitude of the wave). FM = Frequency modulation. The information is encoded by varying the radio frequency The radio portion of the electromagnetic spectrum is divided into a series of bands: Very low VLF 3 to 30 KHz Low LF 30 to 300 KHz Medium MF 300 to 3000 KHz High HF 3 to 30 MHz Very high VHF 30 to 300 MHz Ultrahigh UHF 300 to 3000 MHz Super high SHF 3 to 30 GHz Extremely high EHF 30 to 300 GHz These bands are also named according to the length of the waves (ie the reciprocal of the frequency) As the frequency decreases (and the wave length increases) the effective distance at which the signal can be received increases. UHF is very much "line of sight". By the time you get down to HF, the signal can be bounced off the ionosphere, so can be used over very long distances. FM uses VHF frequencies AM is used over the full range of frquncies. "Shortwave" is another name for the AM HF band. This is the band used by long range broadcasts and amatuer radio. -- Lexacorp Ltd http://www.lexacorp.com.pg Information Technology Consultancy, Software Development,System Support.