I have 5 sections...so, it will be almost 50 ft high tower but one of the
sections has problem in one leg at bottom, so, it is not a perfect triangle
at bottom...for that reason i will use that section buried in concrete...i
will lost 3 or 4 ft instead of 10ft...i will try add another 2 sections in
future to reach near 70 ft.
I will install lightweight antennas...mainly fiberglass and wire...HD
spiderbeam....5 elem on 6m and Inv L for 80 and 160m.
I have the book "Antenna Towers for Radio Amateurs" by Don Dazo, K4ZA...At
the end of the book appear the Pier pin base with a lot of steel bars but
next page appear the Buried section...for 25G, Rohns suggest a 2 x 2 ft by
2´9" ft deep but without steel bars, only the small section (or the lower
side of a 10 ft section like my situation).
73....Douglas, CO8DM
"No creo que haya alguna emoción más intensa para un inventor que ver alguna
de sus creaciones funcionando. Esa emoción hace que uno se olvide de comer,
de dormir, de todo." - Nikola Tesla
----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: <towertalk@contesting.com>
Sent: Monday, January 04, 2016 12:59 PM
Subject: Re: [TowerTalk] Buried section base...and lightning protection.
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
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|