[1000mp] Braid or strap for ground wire...big question.

[Mike Schatzberg]

Hello Yaesu Fans.....

I have read the many posts on this issue....One point which seems to come up
again and again, has to do with "skin effect"....This is one of the factors
which determines the AC resistance of the conductor, and has no effect on
the DC resistance....The skin effect is proportional to the frequency,
increasing with higher frequency, as well as being proportional to the
conductivity of the conductors surface....The higher the conductivity of the
surface of the conductor, the more efficient the transfer of RF energy along
the surface will be...For this reason, coaxial cables, intended for
microwave applications, are generally silver plated, rather than unplated
bare copper...the penetration depth is not very great, again higher
frequency means greater penetration, and silver plated copper conductors
work well....Silver plating is about 8% higher conductivity than
copper....It should be stated however, that the depth of penetration of the
surface current, is so slight at HF, meaning below 30 megahertz, that it is
quite rare to see a cable design for use below these frequencies with plated
conductors....Cables for use at VHF and UHF may benefit somewhat from both
silver plated center conductors, and silver plated copper shields, with a
high percentage of braid coverage....These considerations lead to better
efficiency, and lower losses, with improved structural return losses and
lower SWR.....

At 60 HZ, all of the energy is carried within the conductor, rather than on
it's surface.....

We may be getting grounding for RF considerations confused with the need for
good AC system grounding, and the need to avoid ground loops, as well as
provide protection for induced electrical charging of wiring and antenna
systems by nearby indirect lightning strikes.....Optimum RF grounding
systems are quite a different topic, and their designs are based upon the
intended operating frequency, antenna design, and considerations for the
actual location of the antenna counterpoise, which will vary from place to
place.....Grounding of the electrical system generally benefits from larger
conductors, either solid, stranded, or braided.....the larger the better,
the shorter the better, and solidly joined at all connections....bare
aluminum ground wires suffer from rapid oxidation, which makes long term
connection stability a concern, but are often used because of their lighter
weight and ease of installation......Copper covered steel is often used
outdoors, in electrical system grounds, because of low intrinsic scrap
value, given theft considerations, and hence are used extensively in
commercial applications, in both solid and stranded configuration....Outside
connections benefit from plating, to protect the long term connection
stability of the system, such as tin plating...Copper conductors form Copper
Oxide coatings, mainly Cuprous Oxide, and these oxides are  not
conductive....

Stranded and braided ground straps provide flexible solutions to difficult
grounding situations, where larger solid conductors can not be easily
adapted.....A central ground buss, such as a copper tube, or a solid copper
buss bar, makes a good tie point for electrical grounding, when efficiently
connected to earth ground.....Short connecting ground straps, to the buss,
either stranded or braided, of flexible larger AWG size, properly terminated
on both ends, will also help assure an efficient electrical grounding
system......

By the way,  just a couple of other tid-bits.....the total DC resistance of
a stranded conductor is equivalent to the parallel circuit of all the
individual strands....this is why proper connection at termination is so
important, we do not rely on the interstrand surface connections in stranded
wire, but proper termination of all the strands to each other, as well as to
the connection point....this is what makes proper termination design so
important......since Silver Oxide is fully conductive, discolored silver
plated tank coils are equivalent in performance to bright shiny
ones.....especially at HF frequencies....since Silver does not oxide at
lower temperatures, below 200 degrees C, most discoloration is due however
to formation of sulfur compounds on the silver surface...

Happy DXing and 73,

Mike Schatzberg
WB2AJI
Vice President & Technical Manager
AEB International, Inc.
Atlantic Specialty Wire Division
----- Original Message -----
From: "Don W5FKX" <w5fkx@cox.net>
To: <1000mp@mailman.qth.net>
Sent: Thursday, May 02, 2002 8:18 PM
Subject: RE: [1000mp] Braid or strap for ground wire...big question.


> Well, I guess I'll wade into this one. I believe that Charley/K4VUD raised
> the issue initially. As some have mentioned (but not explained) the
> difference between braided wire (of any kind) and solid wire when used in
> ground paths is in regard to RF vs. DC currents. As far as DC is
concerned,
> there is no difference. However, when it comes to RF currents, there is a
> BIG difference. Because of the self-inductance among the various
conductors
> of the braid, there can be a significant amount of reactance to RF current
> flow that arises. For this reason, it is usually strongly recommended that
> ground conductor paths should consist of solid conductor and NOT braided
(or
> twisted) multi-conductors. Also, since conductance at HF is at
"skin-depth"
> (ie, within the first few atomic layers), the surface area is more
important
> than the volume geometry (ie, tubular is as good as round, square, flat).
I
> use a 4 ft length of 3/4" copper tubing "bar" that spans the back of the
> operating desk, which is then connected to my external ground system with
> 2ga. (~1/4") solid copper wire. All equipment is then tied to the "bar".
One
> of these days, I need to replace the 2 ga. wire with wider, flat, solid
> flex-stock, or 1/2" soft-drawn copper tubing!
>
> 73,
> Don W5FKX
>
>
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