From: ronkean@juno.com
Date: Sat Sep 18 1999 - 15:10:19 MDT
On 18 Sep 1999 16:47:49 +0200 naddy@mips.rhein-neckar.de (Christian
Weisgerber) writes:
> Brian D Williams <talon57@well.com> wrote:
>
> > This of course is why you have a perforated metal screen in the
> > front of your microwave oven, the wavelength is larger than the
> > openings in the mesh, so they can't escape and you can safely
> watch> > so you don't burn your mac'n'cheese.....
>
> Yep.
>
> So why does my mobile phone (GSM ~900MHz) continue to work when
> placed inside my microwave oven (2.4GHz presumably)?
>
> --
> Christian "naddy" Weisgerber
> naddy@mips.rhein-neckar.de
Good question. Microwave ovens work at 2450 MHz, which is a resonance
frequency of the water molecule. Most food has a lot of water in it, so
that frequency is generally effective at heating food.
Check the signal strength meter on the cell phone when it is outside the
oven. If it indicates a very strong signal, you may be so close to the
cell site base that the attenuation of the signal by the oven box is not
sufficient to stop the phone from working. GSM phones periodically
announce their presence to the cell site, about once a minute, I think,
and if the cell site does not get a strong enough signal from the cell
phone it marks the number as temporarily out of service.
People with heart pacemakers are warned to stay away from operating
microwave ovens. That is evidence that the shielding effect of those
ovens is not perfect. Another experiment which might be interesting to
try is to put an AM radio or an FM radio in the oven box. I have not
tried this, but I suspect that the radios will continue to work if they
are tuned to a strong signal. Even inexpensive radio receivers usually
have automatic gain control capability with a dynamic range of 60 or 80
or more decibels. So if the signal strength inside the box is a million
times less (60 db less) than outside the box, the radio might still work,
provided the signal strength outside the box is great enough.
Interestingly, the normal range of human hearing is even greater than
that, about 100 decibels or more.
Just in case, I should state the following, obvious as it may be: Do not
turn the oven on when electronic equipment is inside the oven.
Ron Kean
.
.
.
.
.
.
___________________________________________________________________
Get the Internet just the way you want it.
Free software, free e-mail, and free Internet access for a month!
Try Juno Web: http://dl.www.juno.com/dynoget/tagj.
This archive was generated by hypermail 2.1.5 : Fri Nov 01 2002 - 15:05:12 MST