Frank,
I understand your beliefs, and your explanation sounds reasonable, other
than the pressure of the jacket on braid part. The pressure would only be
needed if the braid were loosely formed around the dielectric.
However, it is empirical evidence that I am seeking. My station ground
system design is based on what I have found in ARRL and other publications
such as the technical documents provided by Polyphaser and Harger. I found
nothing published that spoke of the adverse effects caused by using braided
straps. Your posts are the only source.
Keith
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Frank Donovan
Sent: Sunday, January 16, 2005 3:28 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] There's 'ground', and then there's 'ground'
Keith,
Braid acts exactly as you suggest only when the many small diameter
conductors are under sufficient pressure to cause the RF currents to flow on
the surface of the braid. This is the case with the shield of coaxial
cables or other shielded cables enclosed in a jacket. The pressure of the
jacket causes the RF currents to "jump" from one braid wire to the next so
that it stays on the surfaces of the coaxial cable shield. When water
enters a coaxial cable, the wire junctions in corroded shield become lossy
and the cable loss increases significantly.
Braid straps have no pressure to cause RF currents to reliable flow on the
outer surface of the braid strap. As a result, braid straps have
significantly higher inductance than any of the more appropriate
alternatives for RF conductors, such as solid copper strap, copper tubing,
solid copper wire or stranded wire.
Braid straps work well at low frequencies, but they behave as inductors at
RF frequencies.
I'll leave the proof to the student; however, you can find source material
on this topic in RF engineering and EMC (electromagnetic compatibility) text
books.
You can also find information about good grounding and bonding practices on
the web if you spend a few minutes spent Googling
for: "grounding and bonding" EMC.
73!
Frank
W3LPL
donovanf@erols.com
----- Original Message -----
From: Keith Dutson <kjdutson@earthlink.net>
To: <towertalk@contesting.com>
Sent: Sunday, January 16, 2005 3:59 PM
Subject: RE: [TowerTalk] There's 'ground', and then there's 'ground'
> >Its been well proven that braided strap has far too much inductance
> >to be
> of any utility above 2 MHz.
>
> OK. So where is the proof?
>
> I am thinking any writing you can find is based on the use of braid
> that
of
> poor manufacture or has corroded, or both. Poor or corroded braid can
> act like many very small wires to create substantial impedance.
> However, well constructed braid acts more like a solid bar of metal,
> but with the flexibility required for many installations.
>
> Keith NM5G
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of Frank Donovan
> Sent: Sunday, January 16, 2005 10:35 AM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] There's 'ground', and then there's 'ground'
>
> Here's a clarification, pointed out by an attentive towertalkian:
>
> My previous e-mail was not intended to refer to cables that use a
> braided shield under a jacket. A tight jacket compresses the braid
> and it's a
very
> effective RF conductor, provided that the braid is not corroded.
>
> Rather, my comment was intended to apply to to the inappropriate use
> of braided strap for RF grounding or lightning protection. Its been
> well proven that braided strap has far too much inductance to be of
> any utility above 2 MHz.
>
> So... Lets try again:
>
> Discard all forms of "braided" strap.
> Braid is something a girl does to her hair.
> Braided strap is a poor RF conductor and it's a terrible conductor of
> lightning energy.
>
> Use braided strap only for DC and audio applications, its just an
> inductor for RF or lightning protection applications.
>
> Here's an excellent reference from the many industry sources on this
topic:
> http://members.cox.net/pc-usa/station/ground5.htm
>
> 73!
> Frank
> W3LPL
> donovanf@erols.com
>
>
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers",
> "Wireless Weather Stations", and lot's more. Call Toll Free,
> 1-800-333-9041 with
any
> questions and ask for Sherman, W2FLA.
>
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>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers",
> "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
> _______________________________________________
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
_______________________________________________
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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