Sunday, 8 December 2013

Technical Note

Yesterday I bought an el-cheapo charger off eBay for my new laptop - I always like to keep one in my briefcase for instant travel so I don't have to dismantle the rat's nest of wires under my desk (I have a spare laptop charger, phone charger, electronic ciggy battery charger and extension cable, along with sox, jox and a couple of shirts).

Plugged it in to test it and for some reason I couldn't get on the Net. Phoned BT Broadband, as I naturally assumed there was something wrong with the service, especially as it affected every wi-fi device attached to my home network.

After much mucking about and resetting of the router, the Indian gentleman from BT suggested I try a wired connection, so I unplugged the laptop from the charger and took it over to the router to connect a cable. Worked perfectly. That narrowed the problem down to the wi-fi.

BT man then made an adjustment to the wi-fi channel remotely; I unhooked the wired connection and it still worked perfectly. I gave BT man my thanks and rung off, took the laptop back to my desk, plugged in the charger and - the wi-fi had collapsed again.

Being in the microwave business myself, I suspected something was causing Radio Frequency Interference (RFI). It could only have been the laptop charger, which contains a transformer. I guessed the suppressor had failed.

Subsequent tests proved my theory - don't be tempted to buy cheap laptop chargers. Not only can they interfere with your wi-fi, they can also go up in smoke. Additionally, no amount of tin foil will create a Faraday Cage (I tried).

1 comment:

  1. Laptop chargers are a switch mode power supply which basically used a high frequency oscillator to 'chop' the mains down to the 20 volts or so for your laptop. Cheap ones can cause interference as you have discovered. No amount of screening will help, the output lead acts like an aerial.