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Re: FDC cableing




Hi Joe,

If at all possible we want to avoid capacitively couple all signals to
ground. Therefore, I do not think you want to eliminate the copper. Also,
realize that the DC resistance of the thin Al may be quite high.

Elton.


Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton@jlab.org
(757) 269-7625

On Thu, 7 Jun 2007, Joe Beaufait wrote:

> Hall D Electronics:
>
>  To Elton:  I am more worried about the high frequency than the low. Any
> low frequencies can be filtered out without affecting data, so removing
> the braid still sounds good to me.
>
>  To Fernando: The large amount of copper in the braid is much denser
> than any of the plastic and is a radiator. If we can get half to 3/4 of
> it out of the cable, that has to be a huge improvement on the multiple
> scattering front. With hundreds of cables there is over a thousand ft of
> cable in the bore, it would probably remove > 25lbs of copper from the
> active area. It will also decrease the diameter over all.
> Joe
>
>
>
>
> Fernando J. Barbosa wrote:
> > Hi Joe, Gerard, Dave and Elton,
> >
> > One more suggestion?
> >
> > I suggest we get a full picture from the manufacturer regarding their
> > design criteria for the electrical and non-electrical specs before we
> > start designing a new version of the cable. I am not convinced that
> > removing the braid will improve things. After all, we have space and
> > the metal in the braid is a small fraction of the total material, right?.
> >
> > I also concur that whatever we order must be in the final design
> > configuration.
> >
> > Regards,
> > Fernando
> >
> > Joe Beaufait wrote:
> >> I am glad we have decided to go ahead and purchase a sample of the 25
> >> pr. cable. This cable is going to be the standard for much of the
> >> data acquisition system and it would be very nice to see how hard it
> >> is to work with.
> >>
> >> On that note, there were some comments made at the Wednesday FDC
> >> meeting  concerning the possible redesign of the cable. Daniel
> >> mentioned that we might ask to make the outer jacket thiner and I
> >> promised to look into it but, while looking at the cable diagram I
> >> also noticed that this cable is double shielded. It has an aluminized
> >> mylar layer with drain wire, and a copper braid. I believe we could
> >> do away with the copper braid and reduce the copper in the cable by
> >> at least half.
> >>
> >> I would like comments from the group on whether or not you would like
> >> me  to pursue this.
> >>
> >> Thanks
> >> Joe
> >>
>
>
>
>