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

[Tom Rauch]

As far as resonances, mutual coupling is so high a braid acts just 
like a single conductor. It does not provide "multiple paths and 
multiple resonances", so far as DC through HF is concerned. That's 
folklore.

> 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)

Calculating inductance is a task beyond my time and capabilities, but 
from experience I observe little difference in the inductance of a 
braided or stranded conductor and a smooth conductor. 

There is, however, and easily observed difference in resistance 
between the two.

For example, in tank circuits a thick braided conductor removed from 
RG-8 coax has about the same current handling capability as a small 
number 16 or 18 solid wire. The looser or dirtier the braid, the 
worse the braid behaves.

The type of lay also has a large effect. Densely woven or twisted 
braids or stands, especially those with fine stands, have much more 
heating and loss for a given conductor size.

The primary loss mechanism in coaxial cable that has been internally 
exposed to moisture is corrosion or tarnish on the braid. As a matter 
of fact if the cable has a smooth solid shield and center it remains  
nearly as good when tarnished as when shiny!

The reason for all of this is skin effect, which tries to confine the 
current to the surface of the conductor. If the surface has weaves 
that cause each conductor to periodically move to the center of the 
wire bundle, current tries to flow across the pressure connections 
between each of the small conductors. If those connections are not 
firmly pressed together, and if they are not clean and shiny with low 
resistance, the surface of the wire behaves like thousands of high 
resistance joints.

The more radical the weave and finer the strand, the worse the 
problem becomes.

Wires with gentle twists only have slightly more RF resistance than 
bare solid conductors, even when dirty. Woven conductors, unless 
physically clean and compacted together tightly, can have incredible 
resistance to high frequency current.

Lightning is not dc, and does not behave like dc. It has significant 
energy content at high frequencies, and the energy peaks in the VLF 
and LF range. That's why braided and densely woven conductors are so 
poor for RF and lightning.
 
        73, Tom W8JI
W8JI@contesting.com