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Math of mobile and cordless phones

By Murray Bourne, 20 May 2007

I’m thinking about buying a DECT (digitally enhanced cordless telephone) for my daughter, after her current phone ceased to function after a lightning strike.

I have concerns about FBS (fried brain syndrome) with any kind of cordless phone. The International Commission on Non-ionizing Radiation Protection (ICNIRP) recommended safety guidelines for the use of mobile phones, as outlined in an article by UK’s Health Protection Agency (link no longer available):

The energy absorption is measured in the quantity ‘specific energy absorption rate’ (SAR) which has the unit watt per kilogram (W kg-1). SAR is closely related to the electric field strength produced inside the body tissues.

So the recommendation is:

SAR should not exceed 2 W kg-1 when averaged over any 10 g of tissue in the head and any 6 minute period for the general public.

As for cordless phones, the conclusion is that they should pose "little risk", since the power required for a home or office-based cordless unit is significantly less than for an outdoor mobile phone situation.

DECT cordless phone SAR values would be expected to be in the range 0.008−0.06 W kg-1, at least 30 times below the ICNIRP guidelines.

Interestingly, for mobile phones, it says:

... the signals from modern digital cordless phones are in the form of 100 bursts every second, each of around 0.4 millisecond (ms) duration. The bursts are at a peak power level of 250 mW, but on average the phone only transmits for 1/25 of the time and so the average power is 10 mW.

Wasn’t the HPA the same agency that told the UK people that there would be no risk to humans from mad cow disease?

For an opposing view on DECT phones, see this TETRAWatch article.

As always, whom do you believe...?

See the 3 Comments below.

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