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RE: [TowerTalk] There's 'ground', and then there's 'ground'

To: <towertalk@contesting.com>
Subject: RE: [TowerTalk] There's 'ground', and then there's 'ground'
From: "Keith Dutson" <kjdutson@earthlink.net>
Reply-to: keith@dutson.net
Date: Mon, 17 Jan 2005 11:32:01 -0600
List-post: <mailto:towertalk@contesting.com>
 
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.
>>>
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>>>TowerTalk mailing list
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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.
>>
>>
>>>_______________________________________________
>>>TowerTalk mailing list
>>>TowerTalk@contesting.com
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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.
>>
>>_______________________________________________
>>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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