# Re: Heat comment (Q: Which ear do you use for your mobile phone?)

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>> The phones get HOT. Lots of electronic equipment gets hot.

> As I understand from the battery and the electronics itself. This is

> important - it does not seem like microwaving the brains as some media put

> it.

How much of the heat is directly transfered, how much by IR and how

much by RF microwaving someones brains may be not so easy to

estimate - but should be doable.

A good starting point would be the power capacity of a cell-phone

battery and its operating time. I would estimate the battery at

something like 5W/h (I still manage not to have a GSM phone myself,

so I cannot check it right away) or less.

The next question would be wether GSM phones' output power is

dependent on the talk/silence intervals (I would expect so).

Then (I guess Richard can easily answer that) one would need

to know the transmitter efficiency (how much of the consumed power

gets converted into RF instead of heat).

I am not an RF (Radio-Frequency) guy, my limit is somewhere just above

100 MHz. I assume a 20% efficiency for a mobile power stage,

and would not be surprised if it turns out to be 10 or 70.

Then I assume max. call duration time 2 hours (I believe typical times

are longer), making about 1h talk time (and 1h listening...).

If all 5W/h are gone during talk time (actually it will be less),

at 20% efficiency, we have 1W/h of RF to worry about. Let's say the head

gets 1/3 of it for simple geometric reasons, so what we actually

have at the end would be about 330 mW continuous power to dissipate

I expect reality to be a tenth of such a (deliberately) pesimistic guess.

If one wants to know for sure, measurement is the name of the game.

Take a more or less head-like shaped glass of room temperatured

water, place a cell phone next to it with no direct contact

and perhaps with some black paper between to stop the infrared,

then make the phone talk until its battery is exhausted (it

must have been newly charged at the beginning). At the end,

you  can measure the water temperature to see how much  of

the battery energy got there... Heat transfer water to ambient

air would probably be negligible, as the temperatures will

remain  pretty close; anyway, this can be accounted for by

separately measuring the temperature resistance. If termo

isolation proves difficult (may be the case over a long time),

repeat the experiment with a resistor instead of a cell phone

afterwards (the resistor must consume the  battery in more

or less the same time),  and take the difference. Oh yes,

to not introduce any additional heat by the talking device

(a loudspeaker or - worse - someones head) connect directly

to the phone's mike and provide some (properly attenuated)

signal from some far source.

Well, I intended to write a line or two. Here is what I ended up with...

Hope it is of some value.

Dimiter

http://transgalactic.freeyellow.com

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