Chapter 4. Repeater SpacingMaximum Section Loss A span line includes one or more repeater sections. Typical maximum section loss is 32 dB (normal section) measured at 772 kHz. In the end section next to the central office, maximum loss is limited to 50 to 70% of the normal loss limit, or about 23 dB. In some early line repeaters, the ALBO equalizer has a range of 6 dB to 31 dB. See Figure 7. In many newer line repeaters, the ALBO has a range of 0 dB to 35 dB. This means that the signal can be attenuated through up to 35 dB of cable loss and still become regenerated properly. In practice, repeater sections are designed with a safety factor of several dB, so spacings of 28 to 32 dB are quite common.
Figure 7 Minimum Section Loss The minimum section loss is frequently set at 9 dB because of repeater design and to attenuate reflections. In other words, loss is generally added via a XMT span pad or via a 7.5 dB equalizer in the office repeater for the end section. Equalizers help control near end crosstalk (NEXT) by simulating cable attenuation characteristics whereas the pad displays flat loss. Cable Loss Measurement If a maximum length section is engineered, cable loss should be measured before the final repeater location is established. This allows for changes and small errors. Note that aerial cable can be exposed to higher ambient temperatures compared to buried cable and ducted cable. Higher temperature equates to higher copper attenuation and DC resistance. For design purposes, the losses for aerial cable are estimated at about 5% higher than for buried cable.
Example: One section of 6250 feet of 22 AWG PIC, D-shield, filled, buried has a loss of approximately 26.2 dB. That leaves a nice safety margin. Example: One section of 6000 feet of 24 AWG PIC, D-shield, unfilled, aerial has a loss of approximately 35.2 dB. This exceeds the line repeater capability and could be a problem performer. This exceeds the 35 dB limit for typical line repeaters. Example: One end section of 2200 feet of 24 AWG PIC, D-shield, unfilled, buried has a loss of approximately 12.6 dB. This is far less than the 50% guideline, so it is somewhat wasteful. This should be stretched out. Example: One end section of 5200 feet of 22 AWG PIC, D-shield, unfilled, aerial has a loss of approximately 24.7 dB. This exceeds the 70% guideline and should be avoided. T1 Repeatered Lines In the case of a CO to CO T1 repeatered line, there is normally one Originating Office Repeater and one Terminating Office Repeater. The convention is that the Originating end powers the line with simplex readings of +V and -V, where the -V is typically 10 volts more in magnitude with respect to the +V. If both ends originate power, then there may be a simplex power loop strap set at one of the line repeaters out in the middle of the span. Note that the voltage will appear at the span line interface even if that is open loop. Current will not flow into an open loop, however, so the voltage sensed across the 10 ohm current sensing resistor is the best indication of the validity of the simplex current. The newer ASPR Originating Office Repeaters may be "universal" which means that a mid-span loop strap is not required and powering is shared by each end.
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