Re[2]: [TowerTalk] What's a "Good Grounding System"??
Bob Otto
Bob Otto <N8NGA@one.net>
Fri, 27 Oct 2000 09:39:07 -0400
Hello Jerry,
Lots of questions to answer.....let me take them one at a time.
The tower is a Heights Tower Systems freestanding aluminum tower at
96' tall. That gives me 28 Sq. Ft. windsail at 80 MPH in Class B
environment. I'll be placing the following antennas on that tower on a
Chrome Moly mast:
Force12 C31XR
Force12 Mag240N
Force12 WARC 2/2
Diamond H700 2M/440M
I'll also put a Diamond F23A 2M antenna much lower on the tower for a
24/7 packet/weather station.
The rotor will be a Prosistle BigBoy P61
Regarding the rebar and base, Heights requires a 4' diameter, 8' deep
hole with a rebar cage 3" inside the hole/form for my tower. Since I
was building on the side of a ridge (shown in the picture), I decided
to go down 14' to make sure I was on virgin soil. The ridge in that
picture was, in part created - not natural ground. I simply extended
the rebar cage with the same pattern specified by Heights, down to the
bottom of the 14' deep hole.
The specific pattern you should use for rebar should be spelled out by
your tower manufacturer. It also varies depending on the type of
tower you use, as well as the height/size. For instance, a
freestanding tower has much different requirements than a guyed tower,
etc. While too much rebar won't hurt you, not having enough, or not
having it placed in the proper manner for your specific tower COULD
hurt you. Additionally, if you're having your tower inspected, you'll
need this information for the inspection.
If your ground is rock, I suggest more ground rods. Be careful how
you install them though, there must be 2x the distance from the tower
to the ground rod between any two ground rods from different tower
legs. Example, if you put a ground rod 8' from the tower leg, there
must be 16' between the first ground rod, and the closest ground rod
from ANOTHER tower leg ground rod. If you don't follow this, you will
have overlapping saturation areas and reduce the effectiveness of the
ground. I strongly urge you to get a copy of the Polyphaser book
called "Lightning Protection and Grounding Solutions for Communication
Sites". Some of the reading (IMHO) is not as clearly written as it
could be, but the book has a wealth of information. The book will
also spell out how to add additional rods to a single ground line from
a tower leg to insure they are effective and do not overlap each
other. Also, don't give up on length because of rock. Use a heavy
duty, large chuck, hammer drill to drive the rod in as deep as
possible, and cut it off as long as it can be. Again, the book talks
about what to do in the case of rock, and will help you greatly. Don't
be in a hurry -- the results of your installation will be with you a
long, long time.
As to the relatives <G> None that I know of. But then, I've been
surprised before!
I'm posting this to the list as there seems to be several interested
in the tower grounding schemes. Good luck and let me know how it
goes.
73's from.......
Bob Otto
N8NGA@one.net
Cincinnati, Ohio
**********************************************
DXCC 10M ** DX is !! ** WAS 10M
There is a very fine line between
"HOBBY" and "MENTAL ILLNESS"
**********************************************
When trouble arises and things look really bad,
there is always one individual who perceives a
solution and is willing to take command.
VERY OFTEN THAT PERSON IS CRAZY!
**********************************************
Friday, October 27, 2000, 9:02:35 AM, you wrote:
JK> Thanks for all the info and pix Bob...
JK> What make/model/height tower are you installing, and how much antenna area
JK> do you plan? Freestanding? Crank-up?
JK> And if it's not too much trouble, what does your base/rebar cage look like
JK> under the ground? Is everything in the 4-foot-diameter X 14-foot-deep
JK> concrete tube shown in the pix?
JK> My qth has solid rock about 4 feet down in most places, so I can't get an 8
JK> foot ground rod in (except one place where I must have found a fissure....a
JK> lucky surprise, as it was just where the feedlines enter the house.)
JK> I wonder if several 4 foot rods are as good as an 8 foot rod?
JK> 73, Jerry
JK> PS... do you by any chance have any relatives in Green Lane, PA? My
JK> neighbors are Jerry & Sally Otto....
JK> ----- Original Message -----
JK> From: Bob Otto <N8NGA@one.net>
JK> To: Jerry Keller <dxdog@rcn.com>; <towertalk@contesting.com>
JK> Sent: Thursday, October 26, 2000 10:49 PM
JK> Subject: Re: [TowerTalk] What's a "Good Grounding System"??
>> Hello Jerry,
>>
>> Just a postscript to my previous on tower grounding. I wasn't able to
>> make a Ufer ground on my tower (base put in last week). I did make
>> about four connections using clamps to various places on the rebar
>> cage. Next I used #4 solid copper from each clamp to a 6' copper clad
>> ground rod placed in the very bottom of the hole. I made sure that
>> all the "wire ties" used to tie the horizontal rebar to the vertical
>> rebars were tight so there would be a good connection. The best
>> situation would be to weld the connections but that's not practical.
>> I've read a bit on this and even Polyphaser says that most of the time
>> the wire ties make a sufficient connection. Lastly, I also put a
>> clamp on each tower leg rebar and ran #4 solid copper to the same
>> ground rod in the bottom of the hole. My tower base hole was 14' deep
>> as it was on the side of a hill, and was 4' in diameter.
>>
>> Sorry to add this after the fact.
>>
>> I've attached pictures of the base next to the home I'm building. I
>> don't think the list will pass the pictures on (not sure why!?) but
>> you'll have it. The angled room with all the picture windows is the
>> "shack".
>>
>> 73's from.......
>>
>> Bob Otto
>> N8NGA@one.net
>> Cincinnati, Ohio
>>
>> **********************************************
>> DXCC 10M ** DX is !! ** WAS 10M
>> There is a very fine line between
>> "HOBBY" and "MENTAL ILLNESS"
>> **********************************************
>> When trouble arises and things look really bad,
>> there is always one individual who perceives a
>> solution and is willing to take command.
>> VERY OFTEN THAT PERSON IS CRAZY!
>> **********************************************
>> Thursday, October 26, 2000, 10:03:28 PM, you wrote:
>>
>> JK> Bob, AA0CY/3 posted: "
>> JK> Again, as has been emphasized by other posters, a good
>> JK> ground system (and of course there too there are differing
>> JK> opinions on what constitutes a good grounding system) is the
>> JK> most important aspect of lightning portection."
>>
>> JK> Everyone probably already knows the basics... ground each chassis to a
>> JK> common station ground buss, turn the antenna switch to the "common"
>> JK> (grounded) center position when not in use or storms are in the area,
JK> tie
>> JK> the station ground and every other ground on the property to the
JK> service
>> JK> (AC) ground (usually the ground rod directly under the electric
JK> meter),
>> JK> stuff like that.
>> JK> (Maybe there's some disagreement with all that?) But this reflector
JK> concerns
>> JK> towers, so.....
>>
>> JK> Assume a 60 foot tower on a big chunk of concrete with a rebar cage
JK> inside.
>> JK> Exactly what would constitute a "good ground".... or more
JK> particularly, a
>> JK> "good enough ground" to handle whatever lightning strike might hit the
>> JK> tower, and keep it from destroying anything...how many ground rods,
JK> how
>> JK> deep? Anything else? What about "lightning arrestors", "surge
JK> protectors",
>> JK> and the like.... any good?
>>
>> JK> Jerry K3MGT
>>
>>
>>
>>
>>
>>
>>
>> JK> --
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