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Repetitive Electrical Impulse Noise (REIN) can be the cause of frequent loss of the adsl signal from the exchange, and it can also cause a line to perform below its expected performance.

What is REIN?

REIN is when interference from an external power source interferes with the adsl (or other telecommunications) signal. Usually the two should co-incide happily and cause no problems, however on occasions an electrical item can introduce additional noise in the same band of frequencies utilised by DSL. This noise then drowns out the strength of the adsl signal, either causing degradation of achievable speed or even total loss of synchronisation with the exchange.

Whilst all electrical equipment will generate some sort of noise, it should comply with the Electromagnetic Compatibility (EMC) Directives and avoid generating electromagnetic disturbance utilised by radio and telecommunications equipment, but some equipment may either be old, foreign or faulty, any of which can be the source of some adsl problems.

How do I know if my fault is attributable to REIN?

Tracking down REIN faults can prove tricky, and quite often it is down to us the user to diagnose these faults. Whilst BT special faults do have sophisticated equipment to help track down this type of fault, it should be remembered that this type of fault isn't always within BTs remit as it is outside their control.
REIN faults are also more common outside of working hours when more people are at home, turning on and utilising electrical equipment etc.

Most cases are found by careful observations of conditions on their line by careful monitoring of what times the line deteriorates and trying to tie this up with the timing of power sources being switched on. Monitoring your SNR margin from your router diagnostics should provide some helpful insight as to when these problems occur. See also below for some tools to aid SNR monitoring.

Typical REIN sources

This list is not exhaustive but common culprits could be:

•   A current imbalance between two power carrying conductors (Earth leakage fault).
•   Faulty thermostats (Central heating, Immersion heaters).
•   Electrical power supply units (Laptops, Routers, Plasma TVs).
•   Industrial/Commercial power usage (Electric Railways, Electric fences, Electric motors).
•   Decorative electrical items (Christmas tree lights, Touch lights).
•   Security systems (PIR lights switching on and off).
•   Digital Communication Receivers (Satellite and Freeview set top boxes).
•   Internal power and telecoms cables run close together at the End User.

Is there anything I can do to try track down the source of REIN?

If you suspect there is something interfering with your broadband, get an AM/MW radio and tune it to 612Khz. If you hold the radio next to an LCD screen for your pc as an example you would hear a distinct noise. This should fade away if you move the radio a quarter to half a meter away. Hold it by your modem/router and you'll hear the DSL signal.

If you get a distinct noise enveloping a larger area, then this may be picked up by your router causing an SNR problem (or even drop of sync). By using the radio you may be able to get an idea of where the noise is coming from. Switch the suspect appliance off & retest your DSL connection. By distinct noise you're looking for a clear buzz, whistle, clicking etc. White noise or a general shhhhh noise is less likely to be the cause of the problem, same as any radio broadcast. (In the south of the UK you may hear a French radio station from around 612KHz.)

Be aware that any noise heard on the radio is not always affecting your DSL connection, and you may still have REIN issues in the area which will not be picked up @ 612Khz as REIN is often notoriously difficult to pin-point. This method can be a bit hazy so don’t rely on it completely by any means.

Xmas lights are a classic cause, as are noisy electrical appliance with a long length of wire which acts as an antennae. Sometimes you can cure it with a ferrite sleeve (that small cylindrical thing you normally see along your monitor cable which doesn’t seem to do anything) which you can get from electrical suppliers such as Maplin.

Thanks to "Ezzer" for the above explanation on tracking down noise using an analogue radio, which has been taken from his post on the site forums.

Are there any tools to help monitor my SNR margin to aid diagnostics?

This depends on the make, model of your router.

  •  It is possible to set up MRTG on most routers that do SNMP logging, but this is often outside the capability realms of the average user.

Line showing possible REIN fault MTRG graph of a line showing typical REIN symptoms.

Notice sudden and acute drop in SNR Margin, showing the times during which electrical interference occurs.

  •  Routerstats is an excellent tool, which works "out of the box" for several routers.

SNR monitor routerstats RouterStats

-Highly recommended especially if you have a Netgear DG834x
If your router is not one of those listed you may be able to get it to work with a bit of configuration.

More info and download

Screen cap shows Routerstats configured to work with a Voyager 2100 monitoring a healthy line.

  • DMT Tool also does basic SNR logging.

SNR monitor with DMT DMT tool performing SNR monitoring on a healthy line

DMT v7 Tutorial
DMT v8 Tutorial


BT REIN Engineers.

BT Openreach will sometimes get involved in attempting to trace severe REIN problems. Cases such as these require a specialised REIN engineer to diagnose and locate. Often REIN will fall outside BTs remit and they dont get involved as most culprits of REIN are in the home or neighbouring property.

REIN engineers may use a 444B in conjuction with a MW radio to help them locate the source of the REIN. It must be stressed that not all engineers will have access to this equipment.

BT448B REIN tester

RF Tester 444B
Photo provided by Ezzer.



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