On Mon, 15 Feb 2010 07:27:04 -0800, Ron Wanttaja
wrote:
:

Which reminds me: I fly out of a civil field in a notch of the zone
round a military base - where a digital radar upgrade has recently
appeared. I notice that with my mode C active, I seem to be able to
hear an interrogation as a click as well as see a visual interrogation
flash.

These days, I don't get a repetitive once a revolution style
interrogation, but rather a string of clicks when I am inbound (i.e a
threat to military types which do have squitter) in my headset tuned to
the CTAF

The click is most likely your transponder replying to an interrogation
and likely just coupling though the avionics power supplies, but it
might also be RF coupling.

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:0)

All the more reason to safeguard your head from "RF COUPLING".


You can thank Julian Huxley (1927) and Wikipedia for the following:

A tin foil hat is a piece of headgear made from one or more sheets of
aluminium foil or similar material. Alternatively it may be a
conventional hat lined with foil. Some people[who?] wear the hats in
the belief that they act to shield the brain from such influences as
electromagnetic fields, or against mind control and/or mind reading;
they also serve to attempt to limit the transmission of voices
directly into the brain.

Scientific basis

The notion that a tin foil hat can significantly reduce the intensity
of incident radio frequency radiation on the wearer's brain has some
scientific validity, as the effect of strong radio waves has been
documented for quite some time.[2] A well-constructed tin foil
enclosure would approximate a Faraday cage, reducing the amount of
(typically harmless) radiofrequency electromagnetic radiation inside.
A common high school physics demonstration involves placing an AM
radio on tin foil, and then covering the radio with a metal bucket.
This leads to a noticeable reduction in signal strength. The
efficiency of such an enclosure in blocking such radiation depends on
the thickness of the tin foil, as dictated by the skin depth, the
distance the radiation can propagate in a particular non-ideal
conductor. For half-millimetre-thick tin foil, radiation above about
20 kHz (i.e., including both AM and FM bands) would be partially
blocked, although tin foil is not sold in this thickness, and numerous
layers of tin foil would be required to sustain this effect