It depends on what you start with and what you change. From what you are
starting with you could reduce the impedance by probably more than 50% by
adding one 8' rod 8' from the foundation.. your two rods that close together
and that close to the foundation are probably not even as good as 1 rod out
in the clear.
To get an idea of the 'basic' formulae check out this site:
http://home.earthlink.net/~jimlux/hv/grounds.htm
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 17:32
> To: towertalk@contesting.com
> Subject: RE: [TowerTalk] There's 'ground', and then there's 'ground'
>
>
> I read Polyphaser's technical note before installing my system. There is
> a
> lot of discussion about soil conductivity and how adding more rods will
> improve conductivity. Do you have an idea of HOW MUCH impedance would be
> reduced?
>
> Keith NM5G
>
> -----Original Message-----
> From: Gary Schafer [mailto:garyschafer@comcast.net]
> Sent: Monday, January 17, 2005 10:39 AM
> To: keith@dutson.net
> Cc: towertalk@contesting.com
> Subject: Re: [TowerTalk] There's 'ground', and then there's 'ground'
>
> Hi Keith,
>
>
> 2 ground rods is not even a good start for a ground to be blunt.
> Running some radials out from your connection point and adding more rods
> will help lower the impedance of the ground system.
>
> A look on Polyphasers site will provide some good insight as to layout and
> how many you should use for your situation.
>
> Unless you are only concerned with a safety ground I would add more ground
> system.
>
> 73
> Gary K4FMX
>
>
> Keith Dutson wrote:
> > 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.
>
> _______________________________________________
> 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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