Re: Ground box

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-uswest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Dave,

On 9 Apr 01, at 23:00, Tesla list wrote:

> Original poster: "davep by way of Terry Fritz <twftesla-at-uswest-dot-net>"
> <davep-at-quik-dot-com>
> 
> Tesla list wrote:
> 
> > Original poster: "Ray Robidoux by way of Terry Fritz
> ><twftesla-at-uswest-dot-net>" <robidoux-at-basystems-dot-com>
> 
> > Hi Malcolm,
> 
> > Thanks for your explanation, but I am still confused.
> 
>  Likewise.  Runs counter to my experience, but I'll
>  not debate the observations.
> 
> > My experience does not agree. I am using an 8" piece of
> > braid right now in my primary. It is the wire that
> > forms the connection for my tap on the primary down
> > to the SG. I have touch this many times, while tuning
> > for example, and have found this piece of braid to be
> > STONE COLD. I have NEVER found this braid to be even
> > the slightest bit warm, but ALWAYS as I have said above
> > "stone cold".
> 
> > Also your explanation of how current, "has to hop from
> > one strand to another", makes me wonder about stranded
> > wire in general. In a standed wire don't those strands
> > have to "duck and dive under each other along the length",
> > as well.
> 
>  Not usually.  Take the insulation off a piece, carefully.
>  Have a careful look.  The strands spiral predictably
>  and in a controlled fashion around each other.  They
>  do not duck & dive.
>  (use a large ga wire, or a magnifier on small gauge).

Agreed.
 
> > That would seem to put stranded wire in the same
> > category as braid.
> 
>  cf above.
> 
>  An exception (i think) is proper litz wire....)
> > > -----Original Message-----
> > > From: Tesla list [mailto:tesla-at-pupman-dot-com]
> > > Sent: Sunday, April 08, 2001 5:54 PM
> > > To: tesla-at-pupman-dot-com
> > > Subject: RE: Ground box
> 
> > > Original poster: "Malcolm Watts by way of Terry Fritz
> > > <twftesla-at-uswest-dot-net>" <m.j.watts-at-massey.ac.nz>
> 
> > > Hi Ray,
> > >          I can help explain this braidophobia very succinctly:
> 
> > > On 6 Apr 01, at 12:18, Tesla list wrote:
> 
> > > > Original poster: "Ray Robidoux by way of Terry Fritz
> > > > <twftesla-at-uswest-dot-net>" <robidoux-at-basystems-dot-com>
> 
> > > > Hi All,
> 
> > > > I am very confused as to why this list has such a dislike
> > > > for braid. I have seen many comments like this against the
> > > > use of braid in TC work. My experience with braid is
> > > > that for the same amount of copper (and 90+% optical
> > > > coverage) the braid is an order of magnitude better than
> > > > solid wire at conducting RF energy. The reason for this
> > > > is exactly why we use refer tubing in the primary of a
> > > > TC. It is the skin effect, the fact that the center of
> > > > a conductor is useless in conducting RF currents. Therefore you
> > > > want to increase surface area in the conductor to decrease
> > > > current density. When using braid the most important feature to
> > > > examine is the so called "optical coverage". This is the amount
> > > > of light blocked by the strands of braided wire (strand
> > > > density). Braid comes in all sorts of optical coverage(OC), from
> > > > 10-% to 90+%. One can imagine that 20% OC braid is useless, and
> > > > in fact is typically used in conjunction with aluminum foil to
> > > > make it's shielding and conducting properties better. I would
> > > > not use any braid with less than say 90% OC. If you look at the
> > > > pics that Terry has shown, which is going to be the better
> > > > conductor, I find it hard to believe its the center wire which
> > > > has maybe 1/10th the amount surface area than the braid. I would
> > > > like to hear others thoughts on this matter.
> 
> > > Unfortunately, it is precisely the skin effect that works against
> > > braid. There can be no doubt about how poor it is - I have
> > > measured it in a carefully crafted expt. I then went and proved
> > > the point by running a high current primary with a foot of it
> > > included. It got hotter than the brass blocks holding the gap
> > > electrodes.
> 
>  How big were the blocks?
>  Were they cooled by the air from gap (if a rotary?)?

About 2 cu in each. Static gap. Runtime about 30s. It was not the 
heaviest braid available but having seen the effect in action, I 
wouldn't use braid simply because connections do seem to deteriorate 
over time. Well in excess of 50% (and generally closer to 80%) of all 
faults I deal with in electronic eqpt (and I service a lot every day) 
are due to connections of one sort or another.

Regards,
malcolm

> > >       The strands duck and dive under each other along the length.
> > > Since skin effect is trying to keep current near the outer surface
> > > of the braid, the current has to hop from one strand to another at
> > > every point. Result: to RF, braid is like including thousands of
> > > connections in series, and contact connections are generally less
> > > than perfect. Braid was the standout worst performer in my tests
> > > by a country mile.
> 
> > > Malcolm
> 
>  best
>  dwp
> 
> 
> 
>