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Repetitive Electrical Impulse Noise (REIN)

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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 broadband line to perform below its expected performance.

rein shine emi rfi

 ~ What is EMI?

ElectroMagnetic Interference is undesirable disturbance from electrical or electronic sources. Electronic equipment generates electro magnetic fields, that can cause interference with other electronic devices.

There are also natural sources of EMI such as from the sun, the Northern Lights and of course thunder storms.

 ~ What is RFI?

Radio Frequency Interference is undesirable disturbance from electrical or electronic sources that interferes with radio frequency transmission. RFI can often be picked up by nearby wireless devices. I'm sure we've all heard the familiar buzz from mobile phones when near PC speakers.

 ~ What's the difference between EMI and RFI?

The two terms are often used interchangeably, but to be specific EMI is any frequency of electrical noise, whilst RFI is electrical energy produced in the same frequencies used by radio transmission.

 ~ What is SHINE?

SHINE (Single High level Impulse Noise Event) is a single brief burst of noise.

The noise burst will show as a single sharp spike on graphing tools.   Generally these types of noise bursts will cause line errors such as CRCs or errored seconds and may go un-noticed, but they can be sufficient to knock a broadband connection out completely causing the line to resync.


 ~ What causes SHINE?

SHINE is usually the effect of turning on or off of an electrical device at the mains. Sometimes you may hear an audible 'pop' or 'crackle' when the switch is flicked. 

If there is a pattern to the times check that they don't coincide with something such as lighting or central heating timers or thermostats. The adsl connection will normally be perfectly fine with flat SNRm at all other times.

 ~ What is REIN?

REIN is when interference from an external power source interferes with the adsl broadband (or other telecommunications) signal. Usually the two should coincide 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 DSL broadband 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 REIN faults aren't always within BT's 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 linestats should provide extremely helpful insight as to when these problems occur. See below for some tools to aid SNR monitoring.

 ~ Typical REIN sources

This list is not exhaustive but known and common culprits are:

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


~ What is PEIN?

PEIN is Prolonged Electrical Impulse Noise.  PEIN is defined as non repetitive impulse noise events that have a duration between 1ms and 10ms.  Although described as non repetitive it can appear as random bursts with no fixed inter-arrival times.


~ REIN, SHINE & PEIN Summary

Impulse Noise Repetitive? Burst Length Effects
REIN Yes.  Fixed intervals <1 ms Variable SNR, Bit Errors.
PEIN Random bursts 1 - 10 ms SNR spikes, Bit Errors
SHINE No > 10 ms High CRCs/Loss of Sync


 ~ Is there anything I can do to try track down & identify 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.

Tracking REIN MW radio 612KHz

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 broadband 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’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.  Monitoring your SNR Margin is one of the best ways to identify if you may have a REIN fault.

  • recommends DSLstats which works with most Broadcom based routers 

DSLstats monitoring an unhealthy broadband line

DSLStats monitoring an unhealthy broadband line.

DSLStats can be used with most Broadcom based routers to monitor your SNR Margin.

Changes in SNR Margin can indicate the presence of RFI.

More information about DSLstats.
Download DSLstats

  •  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 another 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 don't get involved as most culprits of REIN are in the home or neighbouring property.

REIN engineers may use a 444B in conjunction 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 as there are very few engineers who are specialised in REIN faults.

BT448B REIN tester

RF Tester 444B
Photo provided by Ezzer.

 ~ RFI in the atmosphere

Its quite common for SNR Margin to drop in the evenings.  The amount of fluctuation will also vary depending on your line length.  The two main reasons for decreased SNR Margin in the evenings are:

  1. More people are at home in the evenings and more likely to use electric appliances.
  2. Atmospheric RFI

During the hours of darkness there is increased radio frequency interference in the atmosphere which all broadband lines will pick up to some extent.  During the evening/night the SNR trace becomes jittery and the SNR Margin falls, but the line will recover the next morning.

There are some lines where the RFI affects are so severe and the SNR drops so much that the line may re-sync at a lower value during the night.  These will mainly be rural properties with long overhead line sections.

The basic reason for this is the sun's solar wind which drags the ionosphere section of the atmosphere upwards on the lee side of the earth -ie the nighttime side. This causes the "Heaviside Layer" high up in the atmosphere to rise up (its approx 75 miles up). This layer reflects radio waves.

This higher positioning of the layer allows RFI to propagate over the horizon far easier. Hence the increased RFI during the hours of darkness coming from far and wide all around. This is the same reason why short wave radio signals can be received from a long way away during the night while they cannot be listened into during the day.

Adapted from c6em's post on the forum


 ~ Medium Wave Channels in the UK that may interfere with broadband

Medium Wave/AM radio and adsl broadband share some similar frequencies.  If you live near a radio transmitter, then there is a possibility that this may impact on your attainable broadband speeds.  It's possible to check by looking at your bit loading graph where you may notice certain tones have low or little bit loading.

Each DSL tone will equate to a specific frequency.  If you have gaps in your bit loading graph, you can convert the tone number into its frequency by using our adsl tone to frequency converter.

When you have the frequency you can then check on, to see which/if any stations are transmitting near you and at what frequencies.

Unfortunately there isn't much that can be done in cases such as this although BT may install an RF3 or certain DSLAM manufacturers may use masks to block certain tones. 

MW transmitters that my interfer with broadband

Unfortunately the UK is more susceptible to RFI than most other countries due to MW & LW stations being located close to each other.  Droitwich is an area that has a particularly high ERP (Effectively Radiated Power) because it has 4 strong AM stations which also share some of the same ADSL frequencies.

This particular subject is rather vast to explain in a couple of paragraphs as it helps to have a basic knowledge of DMT & bit loading. Its also further complicated because every single line is different. If you want any further information please ask on our broadband forum.


 ~ RFI from HAM radio

Amateur Radio (HAM radio) is a known source of RFI for DSL.  Ingress on to overhead telephone lines from HAM radio mostly only affects frequencies above 1.8 MHz, so its the latter tones of ADSL2+ and VDSL which are affected the most.

To overcome the issue of interference some DSLAM manufacturers and Telco companies may apply power control notching at certain frequencies. Possibly the best known UK use of notching was done by BE/O2 on all of their Alcatel MSANs which disabled tones 476-499 (2053kHz-2156kHz). 

The well known HAM frequencies which can cause problems for ADSL/VDSL are

  • 1810 - 2000 kHz
  • 3500 - 4000 kHz
  • 7000 - 7300 kHz
  • 10100 - 10150 kHz

I am not aware of any other UK Service provider that uses HAM band notching, although evidence of its use in other European countries such as Poland.

RFI interference
The above QLN shows typical signs suggestive of RFI from HAM/radio. Note also how it can bleed to neighbouring tones.



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Last updated Oct 2014

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