The impact of oil-filled cable design on transmission distance for multi-pair telephone lines is primarily reflected in the following aspects:
1. Basic Transmission Distance Parameters
Wire Diameter and Attenuation Relationship
A 0.4mm diameter oil-filled cable has a loss of 1.64dB per kilometer. With a maximum allowable attenuation of 7.0dB, the transmission distance can reach 4.26km. If calculated with a loop resistance ≤ 1700Ω, the maximum distance is 5.74km (attenuation is 9.42dB).
A 0.5mm diameter oil-filled cable can extend the transmission distance to 6-7km, while a 0.8mm mining-grade oil-filled cable can reach 12km.
Influence of Feed Voltage
The transmission distance of a 48V standard feed is approximately twice that of a 24V non-standard feed. For example, a 0.4mm diameter cable can transmit 4.26km at 48V, while the transmission distance is halved to 2.13km at 24V.