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

Gary Schafer garyschafer at comcast.net
Mon Jan 17 10:49:05 EST 2005 

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.
>>
>>_______________________________________________
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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 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
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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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