On Jun 24, 5:58 pm, Jim Lux wrote:
Dave wrote:
"Art Unwin" wrote in message
...
On Jun 24, 8:21 am, Gene Fuller wrote:
Art Unwin wrote:
When reviewing the shield of coax I see that the circulating strands
follow the same principle
that I advocate for small full wave antennas. Each turn on the
shielding has a compensating return
turn which cancels the added inductance while the wire crosses over
each other to cancel the added capacitances.
If one got a short length of say 2 inch diameter sheathing they could
attach the wires into one complete circuit
for an antenna. One could dip the sheathing into some sort of
insulation if they so which but actually the wires each act as
insulated wire (electricity preferrs not to turn at right angles if it
can go straight) so that is really not necessary .
Does this mean that if one places his finger on a live wire while making
sure to keep said finger at right angles to the wire that no shock will
be delivered? Do ordinary electricians know about this protective
strategy?

73,
Gene
W4SZ
There are a plethoria of papers presented to the IEEE to prove that
the wires in
braiding act like insulated wires.

Any specific citations? I've got some papers on Litz wire, but haven't
found any on braided wire where the component wires are uninsulated.

There's a paper in 1916 Proceedings of IRE by Kennelly, et al.,
"Skin-Effect Measurements of Conductors, at Radio Frequencies up to
100,000 Cycles per Second" But that's litz wire, not bare strands

W.A. Johnson, et al., published "Static modeling of periodic structures
with application to braided shields" in the APS Symposium 2004, but they
assume perfect conductors.

H. Haase and J. Nitsch published "High frequency model for the transfer
impedance based on a generalized transmission-line theory" in IEEE Intl
symposium on EMC in 2001. They model the braiding, but make the thin
wire approximation for the wires, and take limited account of the
proximity effect (like skin effect, except effect of a wire on an
adjacent conductor)

There's a host of papers in IEEE Trans on EMC, but none of them seem to
make the assumption that the wires are insulated.

in fact, a paper such as the 2003 one by Tiedemann in IEEE Trans EMC,
v45, #3, "Current Flow in Coaxial Braided Cable Shields" makes the
comment in it's conclusion: "The interactions between the single braid
wires are very complicated"

However, Tiedemann DOES say that the shield is better modeled by
insulated wires than as a uniform tube, at least as far as shielding
effectiveness... (he looked at 3 kinds of RG-58 from DC to 500 MHz)

FWIW, Tiedemann is probably hot stuff on this topic.. His PhD
dissertation was "Schirmwirkung Koaxialer Geflectsstrukturen", TU
Dresden, 2001

Jim, I put into google "insulated wire coax IEEE" as near as I can
remember
The abstract stated that the wire acted like they were insulated!
Came across another one that gave the same comment.
I would point out that I am referring to an abstract only as I am not
privy to the whole report
Would appreciate any clarification
Regards
Art