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.
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