4.4. SPECTRUM OF RADIOWAVES AND BANDS OF RADIOWAVES

There follows now an outline of the components of a radiated wave which are used for transmission at various frequencies:

From 30 to 300 kilocycles (low frequency band), the ground wave is largely used for medium-range communication, since it its stability is not affected by seasonal of weather changes. For very long distance communication, the sky wave is used.

From 300 to 3000 kilocycles (medium frequency band) the range of the ground wave varies from to 15 to 400 miles. Sky wave transmission is excellent at night for ranges up to 8000 miles. In daytime however, sky wave transmission becomes erratic, especially at the high end of the band. From 3 to 30 megacycles (high frequency band), the range of the ground wave decreases rapidly, and sky wave transmission is highly erratic on account of the seasonal factors previously mentioned. Space wave transmission begins to become important.

From 30 to 300 megacycles (very high frequency band - or VHP), neither the ground wave nor the sky wave are usable, and space wave (line-of sight) transmission finds major application.

From 300 to 3000 megacycles (ultra-high-frequency band - UHF), space wave transmission is used exclusively.

fig. 25