ngs: (1) it may simply amplify and retransmit the signal at a higher power (non-regenerative repeater); or (2) it may receive the incoming signal, remove noise as best it can through a demodulation/remodulation process, and then retransmit the signal at a high power (regenerative repeater). We use repeaters for two reasons. First, because of the curvature of the earth, the transmit antenna will be hidden from the receiver if we do not place a repeater between the transmitter and receiver (Figure 2.15). Second, repeaters can be useful in reducing the impact of channel noise. Parabolic dish antenna High frequency signal (centered around EM wave 3 GHz, for example) 2 DS-3 Figure 2.14 signals Terrestrial microwave system transmitter 26 mi. 26 mi. Repeater Repeater Transmitter Receiver Figure 2.15 Repeaters Chapter Two Finally, after travelling through the repeaters, the signal arrives at the receiver, shown in Figure 2.16. First, a receiver antenna is applied to return the signal to an electrical signal of a frequency of 3 GHz. Then, a demodulator is applied that returns the high-frequency signal to the original information signal. The terrestrial microwave system just Receiver described typically operates in frequency antenna ranges of 1 GHz to 50 GHz, and it has High frequency electrical signal been applied in a number of different communication systems. For Demodulator example, it has been used as a part of POTS, to connect two EM wave Class 2 switching centers Information-bearing signal separated by terrain such as swamp where it is very difficult Figure 2.16 Terrestrial microwave receiver to lay wire. This terrestrial microwave system has also been set up to connect large branches of big companies. It has also been implemented as a backup to fiber-optic links (later in this chapter). 2.3.3 Satellite Connections With satellite connections, a communication system is set up as shown in Figure 2.17. Here, a transmitter takes the incoming information signal, uses a modulator to turn it into a high-frequency signal, a