Depending on the spacing of the 2 existing rods you could reduce your ground
impedance by 50% or more with 2 more rods. Maybe a LOT more depending on
the exact geometry of the situation. Lots of people make a big mistake by
driving a rod right next to the foundation, you should note that this
reduces the effectiveness of the rod because half of the circle around it is
cut off by the foundation forcing all the current to go in only one
direction.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of Keith Dutson
> Sent: Monday, January 17, 2005 16:26
> To: towertalk@contesting.com
> Subject: RE: [TowerTalk] There's 'ground', and then there's 'ground'
>
> There are already two 8 foot rods just outside the window. Why would I
> need
> more? And if the argument is for better grounding, please indicate your
> thoughts of the percentage of reduction in impedance I would get in Texas
> Gulf Coast sandy loam (5 feet over iron ore clay). Thanks.
>
> Keith NM5G
>
> -----Original Message-----
> From: Gary Schafer [mailto:garyschafer@comcast.net]
> Sent: Monday, January 17, 2005 9:49 AM
> To: keith@dutson.net
> Cc: towertalk@contesting.com
> Subject: Re: [TowerTalk] There's 'ground', and then there's 'ground'
>
> If you want to spend additional money to add to what you have, I would
> spend
> it on a few more ground rods instead.
>
> 73
> Gary K4FMX
>
> Keith Dutson wrote:
> > AES is the vendor for my Harger bar. The bar was shipped with a few
> > short braids and stainless hardware for mounting. I almost included
> > that roll of
> > 3 inch copper in the order but figured the 1.5 inch braid in my spare
> > parts bin (shown in my earlier post) would do just as well. Think I
> > will place that copper strap order now. Shame that I had to buy those
> > huge copper lugs and use a propane torch and about half a roll of solder
> to get a good bond.
> >
> > BTW, the Harger bar is 1/8 thick and about a yard long, with
> > drilled/tapped holes for light straps and larger holes for bolting
> > heavy straps. It is mounted with bolts through Teflon standoffs.
> > These bolts are not supplied, but several stainless nuts, bolts and lock
> washers are included in the kit.
> > Price from AES is about $70 with shipping.
> >
> > Keith NM5G
> >
> > -----Original Message-----
> > From: towertalk-bounces@contesting.com
> > [mailto:towertalk-bounces@contesting.com] On Behalf Of Frank Donovan
> > Sent: Monday, January 17, 2005 6:23 AM
> > To: towertalk@contesting.com
> > Subject: Re: [TowerTalk] There's 'ground', and then there's 'ground'
> >
> > Keith,
> >
> > You should use braided strap only when RF grounding or lightning
> > protection is not required. Otherwise, use copper strap, copper
> > tubing or stranded or solid copper wire.
> > If you must use braid, use the 1 inch wide braid, and limit its length
> > to not more than one foot.
> >
> > In the Amateur Electronic Supply catalog, 1.5 inch wide copper strap
> > is priced ($99.99/100 ft) about the same as
> > 1 inch wide braid ($92.99). The 3 inch copper strap is
> > even better and is listed in the AES catalog at $139.99 per 100 feet.
> >
> > 73!
> > Frank
> > W3LPL
> > donovanf@erols.com
> >
> > ----- Original Message -----
> > From: Keith Dutson <kjdutson@earthlink.net>
> > To: <towertalk@contesting.com>
> > Sent: Monday, January 17, 2005 12:13 AM
> > Subject: RE: [TowerTalk] There's 'ground', and then there's 'ground'
> >
> >
> >
> >>Now this is the most plausible explanation seen so far. Basically it
> >
> > seems
> >
> >>that there is no valid reason to have measured evidence if one follows
> >
> > sound
> >
> >>engineering practice. Makes perfect sense to me. Think I will
> >>replace
> >
> > the
> >
> >>braid with copper strap.
> >>
> >>Tom, thanks for posting. And thanks to Frank for bringing up this
> issue.
> >>
> >>As a side note, I went back to the Harger site which lists tinned
> >>copper braid as one of their grounding strap options. All of their
> >>braid is flat and tightly woven (not the flattened coax shield found
> >>at most vendors), very heavy gauge, and is bonded to special sandwich
> >>type lugs to keep them absolutely flat at each end. I am thinking
> >>this is a reasonable
> >
> > alternative
> >
> >>to wide strap when one must have the flexibility.
> >>
> >>Keith NM5G
> >>
> >>-----Original Message-----
> >>From: towertalk-bounces@contesting.com
> >>[mailto:towertalk-bounces@contesting.com] On Behalf Of Tom Rauch
> >>Sent: Sunday, January 16, 2005 8:26 PM
> >>To: keith@dutson.net; 'Frank Donovan'; towertalk@contesting.com
> >>Subject: Re: [TowerTalk] There's 'ground', and then there's 'ground'
> >>
> >>
> >>>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.
> >>
> >>Sometimes we can't easily find things that are commonly known or
> >
> > understood
> >
> >>in engineering circles. Most engineers and many hobbyists understand
> >>skin effect, and it only takes a moment to reason through this.
> >>
> >>The problem with any conductor at high frequency is skin effect "pushes"
> >>current to the outside. When the conductor is woven, current either
> >>has to flow from inward moving strand to a surface stand through
> >>pressure contact or suffer a path of greatly increased impedance if it
> >>follows the original strand inside the braid.
> >>
> >>The typical clean copper braid with a basically parallel lay and minor
> >
> > weave
> >
> >>has perhaps four times the resistance per unit length of a similar
> >>width smooth surfaced conductor. Of course it varies with the braid
> >>construction and contact resistance between strands, but that is
> >>generally for better braid that is clean with good pressure contact
> >
> > between strands.
> >
> >>In HF power amplifiers, I have found a good general rule of thumb is
> this:
> >>At 30 MHz is the clean braid from RG-8 cable has about the same
> >>current carrying capacity as #14 or 16 tinned solid buss wire.
> >>
> >>It's quite common to have braided leads of rather large size overheat
> >>and fail even at just several amperes at radio frequencies.
> >>
> >>Many construction standards prohibit braided straps in RF or lightning
> >
> > paths
> >
> >>unless the connection absolutely must have braiding in order to
> >>withstand flexing, and then the braid is often substantially oversized
> >>to make up
> >
> > for
> >
> >>its reduced current capacity. It's my understanding NASA restricts use
> >>of braiding, and I can cite many cases where braiding will either
> >>cause excessive loss or actually fail in high current RF systems.
> >>
> >>By the way, that permanent loss increase you see in coaxial cables
> >>that
> >
> > have
> >
> >>been wet, even after they dry back out? It primarily comes from loss
> >>of strand contact in the weave caused by the tarnishing of conductors.
> >>
> >>If the Handbook tells readers braiding (especially braiding that might
> >>be exposed to moisture) is a good idea in high frequency or lightning
> >>grounds....they are giving bad advice.
> >>
> >>73 Tom
> >>
> >>
> >>_______________________________________________
> >>
> >>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.
> >>
> >>_______________________________________________
> >>TowerTalk mailing list
> >>TowerTalk@contesting.com
> >>http://lists.contesting.com/mailman/listinfo/towertalk
> >>
> >>_______________________________________________
> >>
> >>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.
> >
> >>_______________________________________________
> >>TowerTalk mailing list
> >>TowerTalk@contesting.com
> >>http://lists.contesting.com/mailman/listinfo/towertalk
> >
> >
> > _______________________________________________
> >
> > 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.
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
> > _______________________________________________
> >
> > 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.
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
> >
>
>
>
> _______________________________________________
>
> 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.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
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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