<<the fact that a bottom-mounted antenna will not place our body in a strong
part of the radiating pattern>>
Fred,
Where is the "cone of silence" located on a typical transponder aerial?
Makes a case for sitting right on top of the aerial ( or axially above it,
to be precise)!
Duncan Mcf
----- Original Message -----
From: "europa flugzeug fabrik" <n3eu@oh.rr.com>
Sent: Monday, July 16, 2007 2:30 AM
Subject: Re: Europa-List:Transponders
> <n3eu@oh.rr.com>
>
> RF energy harms body tissue by heating it, as in a microwave oven, which
> is continuous energy. However, my oven on the defrost setting zaps the
> food only periodically, like on for X seconds and off for Y seconds. Also,
> the higher the frequency, the more the heating. VHF does a poor job, and
> 1 gHz (transponder) is better, and that's in the range of a cell phone
> also.
>
> Transponders are spec'd in peak power, and 250W is typical. RF energy is
> transmitted only when we send a "1 bit" during a pulse train time duration
> of 21 microseconds, and how many pulse trains we send is based upon a
> whole bunch of variables. Like how many 1-bits we send. How many pulse
> trains do we send when our reply lamp flashes? Not really relevant, as we
> shall see, but it could be a total of 2 milliseconds worth, as a guess.
>
> So, 2 ms every 2000 ms cuts our avg 250W RF power to an average of only
> 250mW, roughly our cell phone's typical power (to save battery, they cut
> themselves back to minimum needed). This comparison is not a good one,
> because we would need to multiply the transponder's 250mW times a 50% duty
> cycle for sending bits, then by sending typically only 40% of maximum
> bits, times another % because of the significant dead time between between
> each pulse train we send, and finally by another % to reflect the fact
> that a bottom-mounted antenna will not place our body in a strong part of
> the radiating pattern at all. And of course, unlike the cell phone, the
> distance to our antenna is at least feet away. There's a square in the
> formula for that, so double the distance and we attenuate the radiated
> power by 25%.
>
> So, we're talking about an average handful of milliwatts here rec'd by
> our body. Like trying to heat food in the microwave by turning it on for
> just 2 seconds each hour. In a week, it will still be room temp.
>
> Fred F.
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=124003#124003
>
>
>
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