Kevin... wouldn't this be equally true for braid used indoors to ground each
piece of equipment to a common bus, even though it's not as subject to a
corrosive environment? Shouldn't solid/wide be used indoors as well? Jerry
K3MGT
----- Original Message -----
From: Tom Rauch <w8ji@akorn.net>
To: <towertalk@contesting.com>; Kevin Hemsley <kev@ida.net>
Sent: Wednesday, June 20, 2001 11:47 PM
Subject: Re: [TowerTalk] Braided Ground Strapping
> > TO BE FLEXED." part. I had never considered braided ground straps to be
> > inferior to solid copper wire for grounding. I had also never
considered
> > that there might be a measurable impedance in braided ground strapping
> > when compared to solid wire. I am curious to hear what others thoughts
> > are on the matter. Does it really make a noticeable difference to use
> > solid wire as opposed to braided strapping?
>
> From Electronic Designers Handbook page 8-25, in the section on
> transmission line..
>
> " When the outer conductor is not solid but is braided to give
> greater flexability, the attenuation in decibels per unit length due to
> resistance of the outer conductor is multiplied by a factor of
> approximately 2.75."
>
> That is for a dense, clean, braided conductor that is compacted by
> the jacket. I have other textbooks that quote even larger resistance
> changes.
>
> If you loosen the braid, so the conductors do not lay in pressure
> contact, the resistance skyrockets. My own measurements of
> braid from RG-8 cable, when removed from the cable, show clean
> fresh braid from RG-8 heats and discolors with only 8 amperes of
> 30 MHz RF. The temperature rise is about the same as a #16 solid
> wire!
>
> I visited an amplifier manufacturer and saw a prototype with RG-58
> braid from the ten meter tap of the tank to the switch. I made an off-
> hand comment to the effect "that outta get hot fast". The engineer
> snickered, fired it up, and then had his smile fade as the braid
> actually smoked and melted. He stuck in some #10 solid wire, and
> it ran cool as can be.
>
> The tarnished braid of coax that has been wet inside is by far the
> primary loss mechanism in a failed cable.
>
> Knowing what a few amperes of RF can do to braiding that is not
> clean...and with pressure between the contact points on weaves....I
> sure would hate to depend on it for lightning or RF grounds.
>
> NASA and others prohibit the use of braiding in lightning grounds,
> and you'll never see it in BC stations where the ground is involved
> in lightning or RF applications unless it is way overkill size and very
> short.
>
> One thing that doesn't hurt the system quite as much are parallel
> lays of wire that are not woven. In that case you loose only a little
> bit of effective surface area for RF, because of the stand-to-strand
> air gap at the surface. The current pushes to the outside edge of
> the individual conductors, so each individual tiny conductor has
> only a fraction of its cross section carrying current...and only the
> conductors on the outside carry any current.
>
> That's the reason Litz wire starts to fall apart at 100KHz, and by 1
> MHz or so is ineffective.
>
> People forget the current migrates to the outside edges of
> conductors, away from the wire core. Keep that in mind, and you
> can picture the problems when the conductor weaves in and out or
> when you rough up the surface by stranding or weaving the small
> wires to make a large conductor.
>
> Smooth and wide is best by far for RF, unless you have no other
> choice. That's while the foil is UNDER the braid of low loss coax,
> and why hardline has solid center conductors and shields.
>
>
>
>
> >
> > Also, does anyone have any thoughts on using a flat copper common buss,
as
> > opposed to copper tubing?
> >
> > ----------------------------------
> > Kevin Hemsley
> > kev@ida.net
> > KB7TYA
> >
> >
> >
> > List Sponsor: Are you thinking about installing a tower this summer?
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> >
> > -----
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>
>
> 73, Tom W8JI
> W8JI@contesting.com
>
> List Sponsor: Are you thinking about installing a tower this summer? Call
us
> for information on our fabulous Trylon Titan self-supporting towers - up
to
> 96-feet for less than $2000! at 888-833-3104 <A
HREF="http://www.ChampionRadio.com";>
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> -----
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List Sponsor: Are you thinking about installing a tower this summer? Call us
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