Knowledgebase

WiFi in homes and schools

EMR Australia - Monday, July 11, 2016

When it comes to WiFi, are we exposed to more radiation from routers in schools or in homes?

This is what electrical engineer and Director of Powerwatch has to say:

(a) The school routers that I have measured have not been worse (i.e. more powerful) than home routers per se. There are also often many of them (1 to 3 routers per classroom or hall are common) which increases the RF power density.

(b) Power density levels with multiple users will always be significantly higher than with 1 or two users – the max signal level in volts/metre does not change much, but the power flux density does as all the devices transmit and the router has to transmit much more of the time to supply data to all the users. When 20 users are browsing, etc, a router is transmitting about 100% of the available time rather than 5% of the available time. So with 20 users the power density is usually likely to be 10 to 20 times greater in the room.

(c) Increasingly school and business routers have transmitter power control which, when set up properly and when the devices in the classroom also have transmitter power control, the levels in the classroom are generally lower (by at least ½ and often much better than this) compared to when it is not implemented. That turns the power down when the router and the connected device are close and therefore don’t need full power to communicate. https://en.wikipedia.org/wiki/Power_control Most countries now require TPC in the 5 GHz WiFi bands, but it is less common on the old 2.4 GHz band. So all routers and connected devices should work in the low frequency 5 GHz band (limited to 100 mW max) and should not generally be enabled to use the 2.4 GHz band. Some routers require all attached devices to be capable of TPC before the router uses TPC – this should be checked out in every establishment as one rogue device can effectively then disable the TPC for everyone. Recent routers should not have this problem – but check for it.

(d) All school WiFi/wLANs should implement transmitter power control and all devices used in the classroom should also have this ability and it should be enabled. It also reduces interference issues and saves on power.

(e) Unfortunately, the beacon signal is essential with multiple users for synchronisation purposes and for the network to work acceptably fast (so users don’t have to have a comfort break while they are waiting for their data to arrive!).

(f) The highest exposures to the children will be from their laptop PCs or tablets (especially iPads which have WiFi only SARs from about 1 to 1.4 W/kg – similar to high SAR mobile phone handsets (cellphones). Ridiculous.

Alasdair Philips (BSc(Eng), DAgE, MIAgE, MIEEE)

(Reproduced with permission.)

 



About The Author - Lyn McLean is a consumer advocate, author and educator and has been monitoring and writing on the subject of electromagnetic radiation (EMR) for over 20 years. She is the director of EMR Australia.


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