signal is one for which Equation 10.6 is finite. The demand from other broadcasting stations. condition that must be satisfied is given in expression 10.7. By international agreement medium waveband broadcasting sta- tions in Europe are spaced at approximately 9000Hz apart. The (10.7) receiver is therefore confined to about 4500Hz SO as to avoid interference. The bandwidth for a television picture signal depends on a number There are many signals that do not satisfy expression 10.7. Peri- of factors such as: the number of lines that make up the picture; the odic signals are the principal group although there are also some number of fields transmitted per second: and the duration of the aperiodic signals that are included in this group. If this expression synchronising pulses. In general the normal bandwidth is 5.5MHz. is not satisfied, then it is more appropriate to consider the average The bandwidth of the audio signal is 20Hz. A colour television power of the signal. If a one-ohm basis is considered then the picture consists of a brightness (luminance) component which average power. from Equation 10.6, is given by Equation 10.8. corresponds to the monochrome signal plus colour (chrominance) information which is transmitted as amplitude modulation side (10.8) bands of two colour sub-carriers which are of the same frequency approximately 4.434MHz but 90 degrees apart. No extra bandwidth is needed to accommodate the colour information. A power signal satisfies the condition given in Equation 10.9. 10.4.4 Radar (10.9) When a radio wave strikes an object some of the energy in the signal is reflected back to the transmitter SO that the object may be de- Therefore an energy signal has zero average power and a power tected. If the transmitted radio wave is in the form of pulses, then by signal has infinite energy. Thus this type of signal classification is measuring the item delay between the transmitted and the received mutually exclusive. However, there are some signals that fit into neither classification. pulse (th