REFLECTOR: Transponder Antenna

[Chuck Jensen]

This transmission irradiation concern took on a real life when highway
patrolmen and local county-mounties started coming down with cancers of
the private area at an unusually high rate, certainly more than enough
to be statistically significant.  A short investigation found the cause.
Because hand held speed detection radars were always on and police
didn't want to alert the radar detectors of the oncoming traffic, they
would hide the radar unit in their lap.  Ooops.

Now, the hand held units have instant-on, so it doesn't emit radiation
until the button is pushed so it doesn't alert oncoming traffic and the
cop doesn't need to hide it in his lap.  However, the output of these
old radar units was massive compared to a transponder, so the lessoned
learned here tells us little about protection from antennas in GA
aircraft, which is likely not needed.

Chuck Jensen


-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Douglas Holub
Sent: Wednesday, August 15, 2007 12:39 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Transponder Antenna


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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