Subscriber loop – is a pair of lines connecting the subscriber to the local exchange. It is a dc loop that serves as the path for the following. 1. Talk battery
2. AC signaling
3. DC signaling
4. Varying dc signaling
Commonly used Term in Subscriber Loop Design
* Cable – it is an assembly of conductor in protective coverage sheet arranged so that the connection can be used singly or a combination of it. * Underground cable - it is a cable install beneath the surface of the earth inside a conduit but in such a manner that it can be removed without disturbing the earth surface. * Aerial cable – it is a cable suspended on poles or other overhead structure. * Distribution cable – it refers to an aerial subscriber cable extending away from a main aerial feeder, a branch aerial feeder, or from a cable to which distribution terminal are directly replace for service connection. * Entrance cable – cables that are connected to an open wire line or cable and bring it to a building. * Feeder cable – cable extend from local exchange main distribution frame (MDF) to the general area where telephone services are to be provided. * Buried cable – cables that have been directly covered with earth surface in such a manner that the earth surface must be disturbed to remove it.
Subscriber Loop Length Limits
Two basic criteria that are considered when designing subscriber loops and limit their lengths are the ff. 1. Transmission design criteria – refer to AC loop loss at reference frequency measured in decibel or neper. Also known as attenuation limit. The reference frequencies are: a. 1000Hz
2. Resistance design criteria – refer to current and resistance drops in the line. Also known as signaling limit.
Basic Resistance Design
Basic resistance of a single rounded wire express as:
For rounded copper wire:
The dc resistance is equated as: