Editing Loading coil (section)

====DSL====
With loading coils, signal attenuation of a circuit remains low for signals within the [[passband]] of the transmission line but increases rapidly for frequencies above the audio cutoff frequency. If the telephone line is subsequently reused to support applications that require higher frequencies, such as in analog or digital [[carrier system]]s or [[digital subscriber line]] (DSL), loading coils must be removed or replaced. Using coils with parallel capacitors forms a filter with the topology of an [[m-derived filter]] and a band of frequencies above the cut-off is also passed. Without removal, for subscribers at an extended distance, e.g., over 4 miles (6.4&nbsp;km) from the central office, DSL cannot be supported.