Re: coax braid vs. solid conductor
Subject: Re: coax braid vs. solid conductor
From: Terry Fritz <twftesla-at-uswest-dot-net>
Date: Sun, 01 Aug 1999 19:24:02 -0600
At 04:06 PM 7/31/99 -0400, you wrote:
>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.
I wonder if the effects you see are more a result of the different coupling
coefficients between the tight bundle and the flat larger coil. The
difference in AC resistance is real but really should not make the dramatic
difference you noticed. I suspect the coupling of the large flat coil is
far higher and accounts for the difference in arc output.