By definition, noise mitigation is the reduction of unwanted AC signals that disrupt telephone service. These unwanted AC signals first disrupted voice grade circuits but today they’ve extended their disruption to all aspects of Triple Play fiber to the node.

Realize that all paired copper conductor circuits contain noise. Therefore, it is the goal of field technicians to reduce the noise to an acceptable level for quality voice grade and bandwidth services such as ADSL, ADSL 2+, HDSL, T1, VDSL2, and other bandwidth circuits. Then, if the pair is balanced, the reduced noise will not affect the circuit.

The analysis of noise problems on customer loops cannot be made in a haphazard manner. The many factors which contribute to noise can cause substantial confusion in the analysis of noise problems, if they are not properly isolated and corrective action is not taken in the proper sequence. It is essential that a systematic course of action be followed and specific tests made in the proper sequence.

It is prudent to never take anything for granted when working on noise. Unless such a procedure is followed, much time can be wasted and repeatedly no solution is found. Noise problems can be multifaceted in nature, but in most cases the solution to these problems can be very simple and well within the capabilities of installers and repairmen.

Most telephone circuits are subject to the interfering effects of noise induction, mainly from adjacent power lines, which could render communication difficult, if not impossible, if it were not controlled.

To reduce the effects, telephone circuits are balanced. A balanced circuit is made up of 2 which are electrically alike and symmetrical with respect to ground. This electrically symmetrical circuit is referred to as the Metallic Circuit and is the normal signal path.

The circuit in which 1 side consists of the 2 balanced conductors in parallel (Tip and Ring) and the other side is a return through ground is termed the Longitudinal Circuit.

If the circuit is perfectly balanced, the noise induction will be exactly equal in the 2 symmetrical conductors and will produce no noise voltage or current in the metallic circuit which is Tip to Ring.

However, if there is an unbalance, the longitudinally induced noise will cause some noise to appear in the metallic circuit. The degree of longitudinal balance, or simply the Balance, is defined as the Ratio of disturbing longitudinal voltage or the voltage flowing along the Tip and Ring conductors to the resulting metallic voltage, that is causing signal flowing from the Tip conductor across to the Ring conductor or the signal from the Ring conductor across to the Tip conductor.

This difference in signal flowing between the Tip and Ring conductors is called Circuit Noise or Metallic Noise. It is expressed in decibels and is measured to a quiet line termination. Circuit noise should measure no greater than 20 decibels (dB).

There are 2 reasons that Circuit Noise is greater than 20dB:

1. The pair is unbalanced. When Circuit Noise is greater than 20dBrnC and Power Influence is less than 80dBrnC that pair is unbalanced and something can be done to that circuit to reduce Circuit Noise to less than 20dBrnC even if the last resort is to move the customer to another balanced circuit.

2. The Power Influence is too high. If the pair is balanced and the Power Influence is too high, above 80dBrnC that is a noise mitigation problem. Moving the customer to another circuit will not solve the problem because the whole cable is affected.

The root cause of the high Power Influence is either a bonding or grounding issue, unacceptable interactive distribution power issues or a combination of the two. Voice grade circuits are affected by harmonics of the 60Hz and bandwidth circuits such as ADSL, HSDL, T1, and IPTV over paired copper is affected by high frequency interferers and excessive longitudinal AC current flow.

Systematic analysis is required to determine the root causes otherwise field technicians end up chasing the wrong dog, resulting in excessive truck rolls and repeat reports. Most companies have the right test equipment. The field technicians need adequate training to solve those convoluted noise problems.

Signing off
Questions on problems you are having, tips for others, or comments on my columns: contact me at dmccarty@mccartyinc.com. Check out my blog on OSP® Magazine online: www.ospmag.com/columnists/mccarty/talkback.