Content area
Full Text
How do radio waves get from here to there? In this article we will present some of the basic principles of RF propagation and give pointers on how you can use this information as a radio amateur or SWL.
Have you ever wondered why a signal generated several hundred or thousand miles away reaches your location without the aid of connecting wires? After reading this article you should have a pretty good understanding of how and why this is possible. In addition to discussing basic radio propagation principles and techniques, we will also cover the electromagnetic spectrum; the nature of radio waves; the regions of the Earth's atmosphere; sunspots and how the sun affects propagation; radio propagation modes and parameters; VHF and UHF propagation modes; using propagation charts and making forecasts; the role of personal computers (PCs) in forecasting; and sources of solar, geomagnetic, and propagation indices and data. Before we get into propagation details, let's start with what constitutes the electromagnetic spectrum.
The Electromagnetic Spectrum. The radio spectrum extends from a frequency of a few hertz (Hz), or 10^sup 8^ meters in wavelength, to about 300 gigahertz (GHz), or 1 mm (10^sup -3^ m).
That is but a small part of the total electromagnetic spectrum, which extends to about 1 attometer (10^sup -18^ m), or a wavelength of one-quintillionth of a meter. Figure 1 shows the total electromagnetic spectrum in terms of increasing wavelength (or decreasing frequency).
Frequency-wise, those frequencies in the lowest portion of the spectrum (ranging from zero to 3 Hz) are known as ultra-low frequencies (ULF). Just above ULF lies another band called extremely low frequencies (ELF), which cover a range of 3 Hz to 3 kHz. Above that grouping, ranging from 3 kHz to 30 kHz is the very low-frequency (VLF) range. Next are the low frequencies (LF), from 30 kHz to 300 kHz. The medium frequencies (MF) extend from 300 kHz to 3000 kHz (3 MHz).
From 3 MHz to 30 MHz are the high frequencies (HF). Above HF are the very high frequencies (VHF), from 30 MHz to 300 MHz. The ultra-high frequencies (UHF) extend from 300 to 3000 MHz, or 3 GHz. From 3 GHz to 30 GHz are the super high frequencies (SHF), and...