REFLECTOR: Transponder Antenna

Douglas Holub doug.holub at tx.rr.com
Wed Aug 15 11:39:29 CDT 2007


Here's what Bob Nuckolls says about that, for what it's worth. (I looked at 
my copy of "The AeroElectric Connection" and, amazingly, there is no 
copyright on it.)

"I've read articles with admonishments to builders of plastic airplanes to 
mount transponder antennas far from the cabin as possible and/or provide 
shielding between the antenna and occupants. Aluminum foil applied under 
seat structures is recommended for very male concerns for protection of the 
'family jewels.' The '200-watt' output rating of the transponder is often 
compared with the 600-watt rating of microwave ovens. While the peak power 
of your transponder may be 200 watts, the output occurs for microseconds at 
a time and only when replying to a radar interrogation. Average power at the 
antenna is only a few watts during pulse time. The 600-watt rating of your 
microwave is an average power directly related to the ability to cook. Your 
transponder can't warm anything up much less cook it....  I've not seen any 
studies in the engineering literature that confirm a hazard from this 
source. Energy densities as low as 5 milliwatts per cubic centimeter have 
been suggested as a threshold for harm. Power delivered to any body parts 
from above a transponder antenna ground plane will be well below this level. 
Most of the serious proponents of shielding take the 'better safe than sorry 
route.' Besides, if you are really worried about biological effects of 
electromagnetic radiation, the eyes are much more susceptible to damage. 
Mmmm, perhaps Bausch and Lomb would be interested in a new aviator's 
product. Grounded gold frames with screen wire shields embedded in the 
lenses? Shield your buns if it makes you feel better but don't lose any 
sleep over it if you don't."

----- Original Message ----- 
From: "lawrence epstein" <ljepstein at hotmail.com>
To: <reflector at tvbf.org>
Sent: Wednesday, August 15, 2007 5:41 AM
Subject: Re: REFLECTOR: Transponder Antenna


>I have heard repeatedly that teh Transponder is a high output transmission
> and the antenna should be located as far away from the occupants as
> possible.
>
> Larry E.
>
>
>>From: "Emanuel Lewis" <elewis8 at nycap.rr.com>
>>Reply-To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
>>To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
>>Subject: REFLECTOR: Transponder Antenna
>>Date: Wed, 15 Aug 2007 05:45:04 -0400
>>
>>O 540I wrote a few weeks ago asking about best location for a transponder
>>antenna.  I have a new "sharkfin" type antenna I plan to locate under the
>>copilot seat.  Does anyone have information/experience about the 
>>difference
>>in performance if the antenna penetrates the fuselage so that its surface
>>is outside vs. mounted inside the fuselage?  Also, how about the size of
>>the aluminum plate that serves as a ground plane?
>>Thanks,
>>Manny Lewis
>
>
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