[TowerTalk] Buried section base...and lightning protection.

[Jim Brown]

On Mon,1/4/2016 8:58 AM, Douglas Ruz (CO8DM) wrote:
> Hi,
>
> I am almost ready to build a Buried section base for a 25G tower.

How tall?  What will be on it?

> The hole is 2 x 2 ft and almost 3 ft deep...is it ok for a guyed tower?...it is almost half cubic yard...and about 2000 pounds of concrete.

Rohn recommends more. 3 ft x 3 ft, 4 ft x 4 ft.  More mass in the ground 
is better when the wind blows.

> ..no steel bars inside.

That's BAD -- steel bars help hold the concrete together.  VERY important.

> I need some ideas about the lightning protection...How can i do a good connection to the tower legs to the ground rod ?...

Bond the steel bars together, also put three pieces of copper strap in 
the concrete, bring all out and bond to the tower legs and to ground 
rods. The standard recommendation for rods is to drive them so that only 
enough is above ground to make a connection. Start with a rod by each 
tower leg, than add a rod radially (that is, more distant from the 
tower) that is spaced equal to the length of the rod. The concrete works 
as a ground when connected as above. So if you're using three 8 ft rods 
per leg, one would be 8 ft from the tower, the next 16 ft, the third 24 
ft. Those distances are minimums, and a bit more is better. Bond the 
rods together with big copper (we use #4 in the US, but you may not have 
access to something that big).

For connections to the tower, a special fitting is needed to prevent 
electrolysis from the connection of dissimilar metals. DX Engineering 
sells suitable fittings. As I recall, they place stainless steel between 
the copper and the tower leg.

Install coax and rotator cable inside the tower, and bond the coax 
shield to the tower at top and bottom.  Use wraps of very good tape to 
hold these cables to a tower leg. Don't use TyWraps or other cable ties, 
which will degrade from UV.

Ground the coax shields again where they come into your house, with 
ground rods spaced like for the tower.

Here's my take on grounding and bonding for ham radio.

http://k9yc.com/GroundingAndAudio.pdf

73, Jim K9YC