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Re: Braid etc.

Hi Jim, all,
              Here is the file of wire 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).

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

    Reduction in copper area became quite noticeable for wire 4, 
causing about 4% attenuation over wires 2,3 and a drop in Q of around 
5%. Wire 5 caused signal attenuation of around 10% on 2,3 and a drop 
in Q of about 8%.
    The performance of the twin braid was bizarre and showed attenuation
of around 7% and a drop in Q comparable with wire 5. A single length 
of coax with the outer covering on performed worse than the twin 
coax showing a decline in Q of about 11.5% and attenuation of around 
10%. With the outer sheath removed, Q improved marginally (to a 
decline of around 10%). Removing the polyethylene covered central 
conductor and using the braid alone showed a drop in Q of about 5% 
and attenuation of around the 5% despite having overall copper 
thickness comparable with the LITZ wire.

Draw your own conclusions.  BTW, I did put a foot or so of braid in 
the primary of a coil running peak primary currents around 700Amps 
and found it got considerably hotter than the brass blocks holding 
the gap electrodes.

Malcolm