ARRL

Chpt 2 - Radio & Signal Fundamentals

Chpt 2 - Radio & Signal Fundamentals

This is the real beginning of your Amateur Radio Adventure!  In this chapter, we dive into what makes a radio work - the "radio" and "signals."  The material in this chapter is presented in a "here's what you need to know" style.  References will be provided so that you can learn more about topics that interest you. 

Covering these topics first makes it easier for you to understand the material later on.  You'll also be a better and safer operator.

  • General Introductions and Tutorials on Radio

  • Waves and Spectrum (page 2-3)

    The Wikipedia’s entry on Waves has many links to all aspects of waves: frequency, phase, wavelength, etc.  Links to tutorials and simulations are provided at the end (bottom) of the entry.  You will find a great deal of information about the electromagnetic and radio spectrum in the Wikipedia, as well.

     

    Saying the Same Thing -- Frequency & Wavelength

     

    The formula λ = c / f also illustrates two important relationships between frequency and wavelength. First, as frequency increases, wavelength decreases and vice versa. This is true because the wave is moving at a constant velocity. A higher frequency wave takes less time and so moves less far during the time it takes to complete one cycle. Waves at very high frequencies have very short wavelengths--such as microwaves that have frequencies above 1 GHz. The so-called "long waves" are those with frequencies below 1 MHz, such as those used by AM broadcast stations.

     

    Second, if you know the frequency of a radio wave, you automatically know its wavelength, too! This means that you can use the most convenient way of referring to a wave and still be accurate. For this reason, it's very common for the amateur bands to be referred to by wavelength. For example, it's not uncommon to hear a ham say something like, "I'll call you on 2 meters. Let's try 146.52 MHz." The frequency band is referred to as "2 meters" because the radio waves are all approximately that long. The exact frequency then tells the hams precisely where to tune.

  • Frequency and Wavelength (page 2-5)

  • Modes and Modulation (pages 2-6 through 2-10)

    Modulation

    AM

     

    SSB

     

    FM / PM

    Signal bandwidths – the typical bandwidths listed in Table 2-3 are approximate maximum bandwidths occupied by a signal.  Actual signals can be narrower. Wider spacing may be required for an acceptable level of interference depending on the receiver bandwidth.  For example, a perfect CW signal occupies 0 Hz of bandwidth, but practical transmitters add noise and other signal artifacts so that the resulting signal occupies about 150 Hz of spectrum (the generally agreed on maximum as covered by question T8A11) and an adjacent receiving station may need to be separated by 100 to 300 Hz.

  • Repeaters (page 2-11)