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Mike S. Reinath wrote:
My transponder antenna is behind the pilot's seat only 6 to 8 inches from my lower torso. Should I be concerned about the RF exposure from this antenna this close to my body?
Reply: I wouldn't be. The peak power of a transponder is high, but very low duty cycle and therefore very low average power. Some numbers I have are that the transponder repeats a 21us pulse train 235 times/second under interrogation. Let's assume the interrogation averages 0.1s per second (i.e., 6 degree bandwidth/360 degrees) with 100 W peak, now the average is 21E-6*235*0.1 *100 = 49 mw. Since the average cell phone is in the 1 watt range and is closer to you, I'd worry about the cell phone first, and I believe the evidence shows that the cell phone level is not harmful. (Others may express their own opinion.) So something 20 times weaker becomes a non-runner.
I put a piece of heavy aluminum foil on the seat back under the seat foam. The foil is not grounded to anything. Is this sheet of foil attenuating the RF at all?
reply: Maybe and probably. It's probably reflecting most of the energy back toward the rear of the plane. Depending on distance from the transponder antenna this may be aiding or subtracting that lobe to the rear. The sheet per se is not an attenuator, it is a reflector. There will be a slice out of the forward lobe due to the obstruction formed by the sheet of aluminum.
Charles Patton
LNC2 360JM
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