I2MOV - Radioamatore

Electromagnetic Spectrum



k  = kilo = 10 3                                       M = mega = 10 6                                    G = giga = 10 9

T = tera = 10 12                            P = peta = 10 15                                                 E = exa = 10 18


BAND          NAME                     FREQUENCY                                LENGHT             

  4             VLF                 3  kHz    a     30  kHz                100  km    a     10  km

  5             LF                 30  kHz    a   300  kHz                  10  km    a       1  km

  6             MF              300  kHz    a       3  MHz                    1  km    a   100   m

  7             HF                  3  MHz    a     30  MHz               100    m    a     10   m

  8             VHF              30  MHz    a   300  MHz                 10    m    a       1   m

   9             UHF            300  MHz   a       3  GHz                    1    m    a     10  cm

 10             SHF                3  GHz    a     30  GHz                  10  cm    a       1  cm

  11             EHF              30  GHz    a   300  GHz                    1  cm    a       1  mm

  12              -                300  GHz    a 3000  GHz                   1 mm    a    0,1  mm




At frequencies below 30 MHz is carried on by means of the sky wave. This is a wave that, on leaving the transmitting antenna, would travel on out into empty space if it were not for the fact that under certain conditions it can be sufficiently reflected or refracted, high up in the earth's atmosphere, to reach the earth again at distances varying from zero to about 4000 km from the transmitter. By successive reflections at the earth's surface and in the upper atmosphere, communication can be established over the maximum possible terrestrial distances.


The region in which the waves are bent back to earth is called the ionosphere. This is a section of the upper atmosphere in which the air pressure is so low that "free" electrons and ions can move for a long time without getting close enough to each other to be attracted together and thus recombine into a neutral atom. A wave entering a region in which there are many free electrons will be affected in much the same way as one entering a region of differing dielectric constant; that is, its direction of travel will be shifted.



An elevated number of sunspots increases the ionization of the high region and create favorable conditions for the propagation of the electromagnetic waves with a better reflection. 

D region-located between 50 km and 90 km - maximum ionization at midday disappear in the sunshine.

E region-located between 100 km and 150 km - maximum ionization at midday minimum at midnight, increasing at dawn.

Sporadic E-ocated between 100 km and 120 km .

F1 region - located between 150 km and 250 km - in the night existing an only F that divides in F1 - F2 during the day.

F2 region - located between 250 km and 500 km - maximum ionization at midday decreasing slowly until the dawn. Could reach the maximum of 350 km in winter and 500 km in summer.



Ultimo aggiornamento: 09-01-16