sed, being now increasingly wavelength or the frequency. Domestic receivers may swallowed up in the loose use of the term 'microwaves'. have the scaling in either unit but generally frequency is In addition, there is a more specific classification system used, as it is in professional radio work. Wavelength does for bands in the upper UHF onwards. need to be used when it is involved in determining the This is given in Table 2.5-4 on the basis of the IEEE physical dimensions of antennas and other devices. listings. It has to be said that different versions of these In this book, the range of frequency considered is band classifications are in use across the world and in roughly from 10 kHz to 300 GHz. Table 2.5-3 illustrates textbooks SO that reference to frequency is perhaps the the names for the various sub-divisions of the radio only safe way of avoiding ambiguities. The presentation of the different possible classifications tends to confuse Table 2.5-3 Frequency band designations. rather than enlighten. Frequency Band code Band description Conveying intelligence by radio 300 Hz-3 kHz Extra Low Frequency waves 3 kHz-30 kHz Very Low Frequency 30 kHz-300 kHz Low Frequency When a wave of a given frequency is radiated continu- ously, i.e. a continuous series of sine waves, no 300 kHz-3 MHz Medium Frequency intelligence is conveyed and the signal is called a 'carrier'. 3 MHz-30 MHz This mode of transmission is known as continuous wave High Frequency (CW). Nothing can be heard unless there is a local 30 MHz-300 MHz Very High Frequency oscillator to 'beat' with the carrier and produce a note at 300 MHz-3 GHz Ultra High Frequency the difference frequency. This is referred to as heterodyning. 3 GHz-30 GHz Super High Frequency If the carrier is switched on and off in accordance with 30 GHz-300 GHz Extra High Frequency some kind of code, e.g. morse code, then this intelligence can be interpreted. More generally, for broadcasting the Introduction to RF and microwave radiation CHAPTER 2.5 carrier wave + 1.5A -1.5A 50% ampli