Unicoils – grade 3AF are inserted into telephone cable pairs to improve their transmission frequency over a given range. There are eight variations of the Unicoil giving different turns ratios and inductance in order to improve transmission efficiency over different frequency ranges.
Unicoils (Loading Coils) consist of carefully balanced windings wound on a core of high permeability material and so arranged that a circuit on the windings in parallel is substantially non-inductive. The coils are then epoxy encapsulated in individual screening cans.
Unicoils comply with British Post Office specification CW52 and are suitable for mounting in joints or for building up into joint loading assemblies.