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Re: Braid etc.

Could it be that these measurements actually understate the differences?
While the measurements at 195KHz are no doubt correct, the action in a TC
when streamers occur is at a MUCH higher (and unrelated) frequency than
that or the pri/sec resonance - many MegaHertz.  Or was it resolved in
an older thread that the VHF streamer-based activity seen at the top of
the secondary is never seen at the base and ground system?

Gary Lau
Waltham, MA USA

>Original Poster: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz> 
>
>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