[TowerTalk] There's 'ground', and then there's 'ground'
Gary Schafer
garyschafer at comcast.net
Mon Jan 17 11:38:40 EST 2005
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
>
>
More information about the TowerTalk
mailing list