TELEDYNMCS@aol.com wrote:
> With this in mind, and coupled with skin effect, which is the tendency
> for weak signals to pass around your body rather than through
> it because your body is made up primarily of water, you are in no
> danger of ill effects from a cell phone's non-ionizing radiation, even
> when held next to your head. Remember, it takes 600-1000 watts of
> highly concentrated microwave energy to pop a bag of popcorn or
> defrost tonight's roast for dinner. Your cell phone radiates
> omni-directionally, so only a small portion of the weak signal being
> transmitted is directed towards your head when in use. Skin effect
> causes that weak signal to pass around, not into, your head.
>
> Transponder antennae, on the other hand, in close proximity,
> say closer than two wave lengths, do, IMHO, pose a significant RF
> hazard when the exposure occurs repeatedly over a long period of time,
> even with the short burst duration. This is particularly true for
> those of us, like myself, who are routinely exposed to high levels of
> RF. While the nominal power output of a typical transponder is around
> 250 watts, peak power is usually rated in the two kilowatt range and
> this does not take into account the gain of the antenna. Granted,
> these are indeed short bursts, but why expose yourself to this power
> level unnecessarily, even for short bursts? (unless of course, you are
> beyond child bearing years or have no desire to father children) If
> you keep the transponder antenna at least two wave lengths away from
> your body roughly 96% of the energy is dissipated within this
> distance. Skin effect takes care of the rest.
Hi John
Thanks for you very informative reply I was obviously wrong in assuming
that cell phones are like real phones and carried two way conversations,
but your description does explain those missing bits of the
conversation. As I said before, my limited expertise was, 35 years ago,
as an R.A.F. Airborne radar technician with a specialist radar
countermeasures squadron. I do know how to change the SIM card and
charge the battery of a Cell phone but that's the limit of my knowledge.
Modern electronic devices are simply magic to me.
I feel I have to correct you when you state that the peak power is in
the 2 Kilowatt range. I have checked a couple of spec sheets and to
confirm things I phoned a major transponder manufacturer just to make
sure. Most transponders have a peak power of up to 250 watts not two
Kilowatts.
For example the Trig TT21 has a mean power of less than two watts with a
peak power of 140 watts at the unit connector. I am told that the duty
cycle is less than 1 percent.
The worse one I saw had an input power of 27 watts total with a peak
power of 250 watts. but none I saw had a peak power of more than 250
watts. Remember this secondary not primary radar and the radiated power
requirements are dramatically reduced
I think the comments about child bearing and fatherhood are difficult to
justify at these low powers though at my age with children in their
middle 30's this should not be a major issue for me !
The transponder aerial is Omni directional so as you say only a small
portion of the energy is directed at you, even less than with a cell
phone held to your ear.
In a Europa, if the aerial is behind the baggage bay ( and the fuel
tank) then it is more than likely greater than two wavelengths or 60cms
(23") away from the crew.
Having said all that, I agree with you that we should try and reduce the
risks its just that in the amateur built aircraft arena I think the
risks from the transponder is well down the list of things to get
excited about.
Tim Houlihan
G-BZTH
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