Re: coax braid vs. solid conductor, was coil pictures ando
I don't think capacitance between primary turns could
be a culprit because capacitance is a lossless element.
> Original Poster: "SEBASTIAN R GAETA" <SGTPORKY-at-prodigy-dot-net> >
> Hi All,
> I Tried a comparison test a month ago after finishing my new .25" copper
> tube primary. I had been using a tightly wound primary made with RG-59 coax
> in the past. When I switched to the new primary I noticed a dramatic
> increase in performance. I had to check this out further and find out why.
> Naturally, since copper tubing has no insulation I had wound it with .25" of
> space in between turns. I needed to know if my previous losses were caused
> by the conductor itself or inter turn capacitance. Dielectric breakdown
> would make itself well known so I tossed out that possibility.
> I wound yet another primary out of RG-59, this time with .25" space between
> turns (I approximately took the insulation thickness into account). I
> noticed that the tune point was identical to the copper tubing, and greatest
> of all, the streamer length was identical. This means that the losses with
> my first primary was not due to the cable at all, but was probably due to
> capacitance between turns or possibly proximity effect. When you have
> insulated cable it is very tempting to tightly wind it because it makes for
> a very compact design, but the output will suffer for it. Just for the
> record, all of my primaries are of the flat design. The RG-59 is foam
> dielectric with two shields(the conductor in this case) One is stranded
> tinned copper braid and the inner shield is aluminum foil. The center
> conductor is copper wire and I just let this float, the electrons don't use
> it so I don't bother to either. I have now switched to .018uf mica cap, and
> 9/60 neon. My spark length is 27.5". Next I will put my ball gaps in place
> of the RQ and see if there is any difference.
The question: if you wound a new primary with spacing between turns,
there must have been a difference in the number of turns if it was to
tune to the same frequency as the old primary. Did you take such
differences into account?
I don't think there should be a huge difference between braid
and copper as far as output goes. What I do think is that it is
desirable to minimize circuit losses as far as possible (good
engineering practice) and if it is possible to eliminate heating in
some component, why not? The amount of heating in braid or anything
else is integrated over time as a function of its ability to lose
heat (amongst other things) so the heating is cumulative and not that
horrendous over a short period. Braid does measurably reduce the Q of
a good circuit. In the primary, one has the gap and if some added
resistance appears in the circuit, gap current will be a bit lower
along with the corresponding VI gap loss (assuming V plateaus at a
low voltage which curves I've seen suggest it does).