asy way of refreshing your memory about signal weaken or attenuate the propagated sound energy. Am- transmission is to imagine that you are looking into plitude attenuation per unit length is usually represented a deep long straight tunnel with walls on either side of by the symbol a. you. When you speak, you propagate sound energy Moss, lichen and shrubs growing on the walls will tend along a transmission path down the length of the to absorb high frequency sound better than low fre- tunnel. Your voice is restricted to propagation along the quency sound, therefore your voice will also suffer For example, the coaxial cable connecting the domestic satellite receiver to the low noise amplifier on the satellite dish often carries d.c. power up to the low noise amplifier, radio frequency signals down to the receiver, and in some cases even digital control signals for positioning the aerial. Transmission lines CHAPTER 2.2 F2:PLOT F1 LAYOUT Points 51: Smith radius 1 5.0000 -0.13dB 91.5° 15.25dB 178.5 Message Box Time 0.5 secs Smith F3 PARTS Chart a clines 550 88.5° b clines 660 88.5° file bpf Rectangular F4 BOARD 50.000 a 5.000 GHz er 10.200 1.270 25.400 19.000 Tab microstrip f GHz Fig. 2.2-2 Bandpass filter design using PUFF. frequency attenuation. Frequency attenuation is known Time propagation delay can be specified in three main as dispersion. ways: (i) seconds, (ii) periodic time (T) and (iii) phase There is also a speed or propagation velocity with delay. The first way is obvious, one merely has to note the which your voice will travel down the tunnel. This ve- time in seconds which it has taken for a signal to travel locity is dependent on the material (air mixture of gases), a given distance. Periodic time (T) is an interval of time; its density and temperature within the tunnel. With it is equal to [1/ (frequency in Hz)] seconds. For example, sound waves, this velocity is about 331 metres per if a 1000 Hz sinusoid requires four periodic times (4T) to second. travel a certain distance, then the time delay is 4 