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 Ray,

On 9 Apr 01, at 18:33, 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.
> 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".

I expect milegage will vary depending on the quality of the braid and 
its width. The piece I checked was not all that wide (perhaps an 
ideal example to show the effect up). 

> 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. That would seem to put stranded wire in the same
> category as braid. But I have heard of coilers who say they
> have used STRANDED wire for their PRIMARY coils, without I
> assume excessive heating.

Fair comment. Well, stranded wire came in second worst so no surprise 
there either. If it doesn't get hot then there's no need to worry 
about it. Here is an extract from those measurements:

PERFORMANCE OF WIRE
     The following is a summary of a brief investigation into wire
performance at low radio frequencies.
     Six wires of various types were tested. Copper strap was not
available for the experiments. The wire coming closest to strap in
terms of RF compatability was an 80 strand LITZ wire, each strand
being 0.2mm in diameter.
     Test frequency was about 195kHz. Skin depth at this frequency
is about 0.15mm.
     The experiment consisted of using a 17 foot (+-1 inch) sample
of each wire connecting a secondary coil (aspect 2, close-wound with
0.56mm diameter wire) to earth.
     An untuned primary was used to couple a signal into the secondary and
coupling was greatly reduced (k approx 0.01) to minimize shunting of
secondary impedances by the signal generator. The oscilloscope was loosely
capacitively coupled to the top of the secondary.
     Estimated accuracy for Q is +-2%. If the wire under test changed
signal level at resonance from the previous wire, the signal generator
level was adjusted to compensate before bandwidth was measured to keep
scope readings constant. As tests progressed, wire previously tested was
remeasured to check for change in experimental conditions. The wires were :

(1) Two lengths of coax cable (braid only) connected in parallel
(2) 1.2mm enamelled solid section copper wire (~twice the diameter of
    the coil winding)
(3) 0.3mm enamelled copper (about 1/2 diameter of windings)
(4) 0.063mm enamelled copper (about 1/9 the diameter of the windings) 
(5) plastic coated stranded hookup wire (conductor diameter = 0.44mm) 
(6) 80 strand LITZ (as above) 

In a latter part of the experiment, the polyethylene wrapped inner solid 
conductor of a piece of coax was measured as Wire(7) (diameter 0.59mm). That 
wire was copper coated iron or steel BTW.

RESULTS
WIRE   (1)     (2)     (3)     (4)    (5)    (6)     (7)
____________________________________________________________
Q =    172     189     189     177    172    193     185

 
> I would be curious to get more of your data on the subject.
> I use braid quite a bit and if it is detracting from the
> final objective (Long Sparks) I want to know so that I
> can go on a seek-and-destroy mission if necessary.
> 
> Ray

I was horrified to see how bad the braid was after thinking how 
wonderful it was since it is often used in coax. Thinking of an 
explanation led to my reasoning about the skin effect. It wasn't 
until several years later that someone told me it was chosen to make 
the cable more flexible. The best coax uses aluminim tape for its 
outer conductor. I've seen this used in ethernet cable.

Regards,
Malcolm