[TowerTalk] There's 'ground', and then there's 'ground'
Gary Schafer
garyschafer at comcast.net
Mon Jan 17 13:04:27 EST 2005
An example in one of Polyphasers books shows, with 10 foot spacing of rods,
2 rods gives about 50% of one.
3 rods drops to 40%.
4 rods to 35%.
5 rods to 30%.
6 rods to 27%.
7 rods to 25%.
8 rods to 23%.
With closer spacing there is not as much gain in resistance reduction.
5 ft spacing for 4 rods reduces it to only about 42%.
Keep in mind this is for a particular soil conductivity.
This is from their "grounds for lightning and EMP protection book".
73
Gary K4FMX
Keith Dutson wrote:
>
> 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 at comcast.net]
> Sent: Monday, January 17, 2005 10:39 AM
> To: keith at dutson.net
> Cc: towertalk at 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 at comcast.net]
>>Sent: Monday, January 17, 2005 9:49 AM
>>To: keith at dutson.net
>>Cc: towertalk at 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 at contesting.com
>>>[mailto:towertalk-bounces at contesting.com] On Behalf Of Frank Donovan
>>>Sent: Monday, January 17, 2005 6:23 AM
>>>To: towertalk at 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 at erols.com
>>>
>>>----- Original Message -----
>>>From: Keith Dutson <kjdutson at earthlink.net>
>>>To: <towertalk at 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 at contesting.com
>>>>[mailto:towertalk-bounces at contesting.com] On Behalf Of Tom Rauch
>>>>Sent: Sunday, January 16, 2005 8:26 PM
>>>>To: keith at dutson.net; 'Frank Donovan'; towertalk at 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 at 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 at 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 at 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 at 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 at 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 at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
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