On 23 May 2006 10:17:31 -0700, "K7ITM" wrote:

Seems pretty clear to me, Roy. The effectiveness of a copper strap
around a mains-frequency power transformer at reducing the exterior
magnetic field is well known and often used. It's all very clear from
Faraday's law of magnetic induction: the net magnetic flux through an
area enclosed by a perfect conductor may not change, so time-varying
magnetic fields are perfectly blocked by perfect conductors. Copper's
a reasonable approximation of a perfect conductor in the case of RF
shields.

Hi Tom,

However, Richard's explanation is the analogue of the effectiveness of
a copper strap (with a non-contacting overlap so as to not be a
shorted turn) between windings of a mains-frequency power transformer,
and grounded to provide electrostatic separation of the two circuits.

73's
Richard Clark, KB7QHC