Repetitive Electrical Impulse Noise (REIN)

Elan Telecom and BT Openreach have a lot of experience of REIN effecting our business broadband customers. Repetitive Electrical Impulse Noise used to be just an urban myth. However, business broadband customers tend to be more at risk of REIN as they are more likely to have many electronic devices or heavy machinery in their premises which can cause REIN. REIN is not to be confused with SHINE (Single Isolated Impulse Noise) as the repetitive nature of REIN means it’s disruption to any internet service is often far worse.


As xDSL technology develops and becomes faster, every broadband customer requires a better xDSL line profile with low SNR to achieve a fast and stable connection. However, when you try to modulate more complex forms of xDSL such as ADSL2+ and VDSL; electrical impulse noise – which was present in the surroundings all along – suddenly becomes your worst enemy.

REIN can cause frequent loss of packet data over xDSL connections causing slow internet and in severe cases; cause frequent or complete loss of xDSL synchronisation (the disconnection of your internet service between your xDSL Router and local exchange).

REIN occurs when radio interference from a (usually faulty) power source comes into contact with a copper pair telephone line which is xDSL enabled. This introduces additional noise on the same frequency band which is being used for the xDSL modulation. The additional noise and the native xDSL signals collide. The noise can be louder in amplitude than the xDSL signal however more often than not, it simply wipes it out. In physics, the laws of wave propagation describes this type of collision as destructive interference.

What causes REIN?

All electrical equipment should comply with the Electromagnetic Compatibility Directives . However some devices develop faults, are poorly manufactured/maintained or are procured from sources abroad. These types of devices can produce REIN.

xDSL signals are only susceptible to certain frequencies of REIN. Therefore, the following situations and devices are well-known to most likely cause the ‘perfect REIN storm’:

  • Any device which may have an earth leakage fault.
  • Central heating or immersion heaters or anything which may have a faulty thermostat
  • Power Supply Units for PCs, Routers, TVs, Phone Systems, Monitors etc.
  • Large machinary or industrial/commercial power usage
  • Christmas tree lights or fairy lights
  • Security systems
  • Sky, Freeview and DVD appliances
  • Instances where xDSL cable has been run along side electrical cable.

How can I fix a REIN Problem?

If you suspect you have a REIN fault, you could be in for a long ride with regards a potential fix. BT Openreach will only escalate a suspected REIN case to their specialist REIN engineers once a standard Openreach engineer has run tests and tried to avoid the REIN. Sometimes this is done by re-wiring your premises and applying additional filters to your analogue line. The other important thing to remember is that once the initial engineer is satisfied everything has been done to avoid REIN – whatever is causing the REIN is not on BT’s network. Therefore, not subject to a normal BT service level agreement and therefore the BT REIN engineer may take a couple of weeks to attend site. You may also be charged for this visit as the REIN is likely being caused by an appliance or configuration on your site.

You can see if your internet problem is attributed to REIN yourself and sometimes even track it down. Make a log of the dates and times the internet goes down (any good ISP should be able to provide you with this data). If there is a pattern, like for instance the internet only slows or goes down between 9am -5pm the interference must by an electrical appliance which is active within that time frame. Try unplugging electrical items near the analogue line or router from the mains supply and see if this instantly resolves the issue. Remember when doing this though, xDSL synchronisation (the time it takes for your broadband to reconnect) could take up to 2 minutes depending on your router and line profile.

Another way of checking is to get a cheap analogue radio and tune it to the following frequency: 612Khz AM/MW. Hold the radio next to a PC or screen and you should hear an example of the noise. The noise should disappear as you move a meter away from the device. If you hold it near your xDSL modem/router, you should hear the xDSL signal. If you get a distinct noise, present in a large area, this could cause REIN on your xDSL line. If the noise completely disappears when you switch one of your appliances off, try moving the appliance to another room and seeing if the broadband stays stable.

Note that not all REIN is caused by interference that can be detected at 612Khz and also that the interference is notoriously hard to pin-point. Sometimes you will need the help of BT REIN engineers as they have directional radio frequency detectors at their disposal. REIN can also be present in a very small area but has been known to completely swamp out broadband signals over a 300m radius. REIN issues are further tricky to pin-point as often the faulty appliance is plugged into the mains and thus the mains cable across your entire mains electrical circuit becomes an antenna for the interference, emitting the radio waves throughout all your electrical outlets, lights and appliances.

Remember, to test for the presence of REIN, you can sometimes setup SNR logging on your router or check closely for CRC errors. Another way is to check for electrical impulses using something like an EMF meter or Spectrum Anayliser connected directly to your xDSL line. If in doubt though, escalate the problem with BT Openreach.

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