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.
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.
- Lesson 2 from this collection of animated tutorials on waves illustrates the relationship between frequency and wavelength.
- Wikipedia entry on Modulation- a comprehensive review of modulation
- ARRL Technical Information Service - plenty of articles and links about AM
- Williamson Labs AM illustration page - animated page showing how AM works
- AMfone - a Web site about AM operating on the HF bands
- Williamson Labs SSB illustration - animated page showing how SSB works
- Wikipedia entry on Single Sideband - in-depth treatment with the theory
FM / PM
- Understanding FM Transmitters - a QST article about FM
- Williamson Labs FM illustration page - animated page showing how FM and PM work
- Wikipedia entry on Frequency Modulation - in-depth treatment with the theory
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.