Carriers are generated at a high level (+25dBm) for distribution to circuit link which may contain many stages of translation and the translating equipment. Each equipment normally requires two several tandem connected line systems. Seasonal temperature supplies at a power level of approximately +10 to + 13dBm in order changes to the cable link is foremost in the contributing factors. The to drive the modulator and demodulator. correction is applied equally across the frequency band and with an Automatic Gain Control ratio of approximately 10:1. Thermistors are normally used as gain control elements to avoid Pilots any unlinearity distortion to the traffic path. In addition the slow thermal time constant is suited to the slow diurnal gain change of the cable system and the envelope gain of the AGC relatively easy 20.6.1 Translation equipment pilots to control. I 4dB regulation range is normally required from AGC equipments. Reference pilots are discrete frequencies added to each translated band of traffic channels for monitoring and automatic gain control 20.6.2 Line equipment pilots regulation at the far end of the transmission path. Some of the more common reference pilots are given in Table 20.3. Specific pilots are combined with the traffic path for transmission Additional pilots can be added for measurement or monitoring of over copper line systems. wide band systems and are usually positioned in the gaps between supergroups. These are called intersupergroup pilots. 20.6.2.1 Regulation pilots 20.6.1.1 Use of reference pilots for automatic gain control Regulating pilots are placed at the high end of cable frequency spectrum close to the top traffic frequency where the cable loss is The normal practice is to provide gain or loss correction to the greatest and the pilot most sensitive to any loss changes. The gain traffic path at the received end of transmission using the pilot to of the line repeater is modified to keep the pilot level constant control the correction. (See Figure 20.8). This correction is appl