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ADSL Troubleshooting

Understanding what some of those Modem / Router terms mean like, SNR Margins, Line Attenuation, and Signal to Noise Ratios will assist you in determining the health of your ADSL / phone line.

This ADSL troubleshooting page is written in simple terms to assist people out there who are not technical geniuses.

Please contact us if you think something is inaccurate or should be added. Your comments are very welcome!

Physical connection rate of your modem/router

ADSL Speeds can vary with routers and modems.

Different brand routers have various operating systems known as "firmware".

This firmware can communicate differently depending on the ADSL exchange equipment that processes the information.

Internet service providers (ISPs) will therefore prefer specific brands of modems that they have tested and are comfortable with.

People who don’t have the time to shop around for modems/routers may be better off letting their ISP provide one for them. This will also ensure that your provider will assist you with any difficulties that you may experience.

Line Attenuation

Line attenuation is an indicator of line health. ADSL, Line Attenuation is the energy loss of signal transmission through the phone line.

Several things can cause higher line attenuation, including…

  • Distance from the exchange
  • Type of cable & gauge of wire
  • Phone line joins, such as wire connectors
  • Additional phone points
  • Star wiring
  • Corrosion on your phone line

The lower the line attenuation, the better.

20bB. and below = Outstanding
30dB-40dB.=Very Good
50dB-60dB.=Poor and may experience connectivity issues
60dB and above=Bad and will experience connectivity issues


SNR Margins (Signal to Noise Ratio Margins)

Signal to Noise Ratio simply refers to how loud the signal is over background noise. The higher the SNR margin, the more stable the connection because of fewer errors.

A strong signal will allow the line to cope with faster speeds.

In general, a higher signal to noise ratio will result in less errors.

6bB. or below=Bad and will experience no line synchronisation or intermittent synchronisation problems.
7dB-10dB.=Fair but does not leave much room for variances in conditions.
11dB-20dB.=Good with little or no synchronisation problems
29dB. or above=Outstanding


Calculating your distance from the exchange

A handy equation that we use is to divide the downstream attenuation by 13.81. This will give you a fairly accurate distance from the exchange measured in kilometres.

For example; if you had a downstream attenuation of 30dB…

30dB divided by 13.81 = 2.172 KM

ADSL troubleshooting & your alarm system

Alarm systems, when wired correctly for monitoring, process the phone line first before it has the opportunity to travel throughout the premises or to you modem.

This is referred to as Mode 3 wired. The purpose of wiring your alarm system to Mode 3 configuration, is to ensure it is able to dial out in the event of a break in, regardless if the phone has been accidently left off the hook or if the phone is forcibly removed.

If the ADSL line is the same line being used in monitoring the alarm system, then a good quality Central / Remote Splitter must be fitted to the premises ensuring that there is no broadband signal being processed by the alarm.

In short, alarm systems hate ADSL broadand and modems hate alarms.

Failure to do so can result in ADSL drop outs, slow speeds, synchronisation problems, phone lines cutting out etc.

Poor quality wiring

Line health will be dependent on the existing phone cabling.

Energy is required for ADSL signals to travel along phone cables and turn corners. Therefore, more phone cables / extensions (Star wiring) or phone points connected to the line will result in a poorer quality ADSL phone line or higher line attenuation.

The same goes for corrosion on the line. The more corrosion, the higher the resistance resulting in a poorer quality signal.

The best way to ensure the best quality signal is to have one phone point wired to standard or install a good quality Central / Remote Splitter.

A Central / Remote Splitter will allow many phone line extensions without interference of the ADSL signal to the modem.

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