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Re: Advice on secondary

Original poster: FIFTYGUY@xxxxxxx

In a message dated 1/29/05 11:23:47 PM Eastern Standard Time, tesla@xxxxxxxxxx writes:
P.V.C has a very high dissipation factor, they actually use radio
frequency to weld P.V.C. (albeit at a very high frequency) I do not
recall the exact figures but polyethylene and styrene both have rather
low dissipation factors. (anyone have a C.R.C. handbook handy?)

Could not find dissipation factors in my 83rd ed. of the CRC "Handbook of Chemistry and Physics."
My 2nd ed. of the "Polymer Handbook" lists the following dissipation factors (at 60 Hz!):

    Poly(methyl-1-pentene)                              .00007
    Poly(styrene), general purpose                   .0001-.0006
    Poly(styrene), high impact                          .0004-.002
    Poly(styrene), high heat                              .0005-.003
    Poly(ethylene), {low, med, and hi-density]   <.0005
    Poly(propylene)                                        <.0005
  Poly(carbonate)                                        <.0009
    Epoxy cast resins                                        .002-.010
    Poly(vinyl chloride)                                      .007-.020
    Poly(vinyl chloride), chlorinated                    .021-.019
    Poly(vinylidene  chloride)                             .03-.045

Also lists "Arc Resistance, ASTM-D-495[s]", with Cellulose Acetate, Poly(ethylene) med density, and Poly(imide) at the top, Poly(propylene) high, Nylon 66 and Poly(styrene) middle, Polycarbonate and Epoxies lower, and Poly(vinyl chloride) at the bottom.
From the 1st ed. of the McGraw-Hill "Electronics Engineers' Handbook", a table from "Standard Handbook for Electrical Engineers", 10th ed.", properties of insulating films. Include dissipation factors at various frequencies:

    Material:                             dissipation factor @ 10^3/ @ 10^6 Hz

    TFE tetrafluoroethylene                  .0002/.0002
    Polyethylene                                 .0003/.0003
    Polyimide                                      .0003/.0010
    Polypropylene                                .0003/.0003
    Polyurethane elastomer                      .06/---
    Cellulose acetate                               .10/.10
    Polyamide                                       .010/.016
    Vinylidene chloride                          .045/.075
    Polyvinyl chloride                              .16/.14

So it would appear that polystyrene is low dissipation, and PVC sucks. However, my gut feeling is that this is purely academic, since I've read that after breakout the Q plummets to a whopping 6 or so. I'm guessing a typical secondary coil form won't dissipate more than a percent or two of the total energy of a typical TC. I would also guess drying to remove water content would more help prevent losses through breakdown than from dissipation.
I bet the secondary wire has more losses than the coilform, although again due to low post-breakout Q it can't be that important. If the standard model shows a series 220K Ohm resistance in the streamer, I'd work to make the air more conductive to cut losses!
I think the only folks who would have to worry about coilform dissipation factors are those running in high-power CW.

> Ideally no core at all would be best, Styrofoam is about as close as
> your going to get to no core at all.

Or a form-less coil. But I think it would be fragile compared to a coil that retains its former. One of these days I'll get around to making one - I bought the electrical epoxy to do it, and made up the former. At the moment, I'm happy with the scrap SDR sewer pipe I've been scrounging for free.

-Phil LaBudde