Re[2]: [TowerTalk] New Tower Construction - Questions

[R. Otto]

Hello Bill,

You might want to think about your ground rod plan some more.  I too
thought "the longer the rods, and the more rods I use, the better".
When I read the Polyphaser data, I found differently. They seem to
suggest that length of rod over a certain amount will be wasted. They
talk about ground rods on the order of 4', no more than 8' unless you
have some specific reason for length. Additionally, they say that
additional ground rods on a single line don't really help much as it
takes too long for the charge to get to the extra rods. They also talk
about "sphere of influence" (I think that's correct -- doing this from
memory). What this means is that if you put ground rods too close
together, the ground is saturated with the charge from one and the
charge from the second one, if too close to the first, will not be
absorbed from to ground.

Also, please note the importance of; A) making sure your ground wire
doesn't have a radius less than 12" (or some large amount *memory*
<G>), and B) that it's important to take your coax all the way to the
ground before taking it in your shack.  Don't trust my memory here
though..........use the data Polyphaser recommends.  I'm just trying
to point you in the right direction on several issues I found
interesting, and sometimes contradictory to what I've seen posted.

I had to read the tower grounding information a couple of times to
absorb all the information but after reading it, it made logical
sense.  I too am about to put up a 112' tower and have changed my
plans for grounding & ground rods significantly based on the data.

73's from.......

R. Otto
N8NGA@one.net
Cincinnati, Ohio

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Thursday, August 31, 2000, 10:20:57 AM, you wrote:

BC> On 8/30/00 6:36 PM, R. Otto at N8NGA@one.net wrote:

>>
>>Hello Bill,
>>
>>Couple of things for you to consider.  First, most communities that
>>have building inspection departments will want to see the cage
>>requirements spelled out on a drawing -- signed by an engineer.

BC> In Gwinnett County, GA, amatuer radio towers less than 50 feet do not 
BC> require any drawings or plans. Mine will be about 49 feet, including 
BC> mast. 

>>The cage should be
>>suspended in the hole with wire to insure it's positioned properly
>>when the concrete is poured.  In the finished product, the cage
>>usually isn't any closer than 3" from an outside concrete surface, and
>>the cage is uniformly laid within the space, often on 12" centers.

BC> Excellent, that's the information I needed.

>>Lastly, you should read Polyphaser's report on tower grounding.

BC> I visited their site yesterday and downloaded three PDFs on grounding. I 
BC> haven't yet read them, but I will. I found this information searching the 
BC> TowerTalk archives.

>>A)  It is advisable to use the rebar cage as PART (not all) of a grounding
>>system.

BC> UFER ground. I've heard about it before, and I got the PolyPhaser report 
BC> on it.

>>C)  Part of the grounding system should be a Ufer ground, which is
>>made by placing copper wire in a pattern about 3" from the base of the
>>concrete and tieing it to the tower legs.  More on that in the
>>Polyphaser publication.

BC> Got it.

>>D)  Lastly, go to that publication as well to find out how to place
>>your ground rods for the tower.  I read many comments recently on this
>>list that are in conflict with what Polyphaser says.  A general
>>guideline might be that if you use an 8' ground rod, you should have
>>three rods, one on each leg of the tower - 8' from the tower, and each ground
>>rod should be no less than 16' (double the length) from each other.
>>They give a very detailed explanation on how to calculate what you
>>need and how to set it up correctly.

BC> I had planned 6  10' rods -- three close to the base, and three more some 
BC> distance away.

>>E)  Don't bother to call your building inspector to inspect the
>>base..........who needs that headache.

BC> Not me. I'm doing this "by the book." I want all the approvals that are 
BC> required.

>>F)  Attach one ground line to a tower leg and put three ground rods on
>>that line.

BC> I don't know if my ground setup will come to PolyPhaser's demanding 
BC> standards, but it certainly will be better than this.

>>All kidding aside, there are many more good, constructive things that
>>can/might be done, and I'm sure many of the Elmers here will suggest
>>lots of them.  It's up to you how much effort you want to invest
>>in doing your tower right.  Hope this helps.

BC> Thanks, I appreciate it. Good advise.


BC> Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@atlnet.com
BC> Quote: "Boot, you transistorized tormentor! Boot!"
BC>             -- Archibald Asparagus, VeggieTales



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