Jerry K3BZ wrote:
>I'm putting in a base for a used tower, and I can't get exact base specs
>from the manufacturer (Heights). It's an "old-style" Heights tower, and
>Heights apparently only wants to provide base specs when you buy all the the
>base hardware, and then the specs are for the "new style" anyway. So, I'm
>planning to install an over-sized base in order to cover all contingencies.
The size base needed depends upon the load it must carry. What height
tower; what mast above it; what is wind load of tower, rotator, mast,
antennas, and anything else that will be on the tower; what is weight of
each item; what wind zone are you in or what wind do you wish to design for.
>I understand I'm supposed to wire the elements of the rebar cage together,
>as opposed to welding them, I hope that I have that correct ?
wiring as opposed to welding is recommended for 'non-weldable' rebar.
However, welding is recommended for lightning protection, especially to
make the base an effective "Ufer" ground. That requires purchasing the
correct grade of rebar. I found sources like Menards had no knowledge
of the grades and the rebar they offered was not marked and had no
documentation. For a slightly higher price, I bought graded rebar from
one of the better quality redimix suppliers and they cut it to length
for me. It welded fine with E7018 electodes. If you have difficulty
finding a supplier with knowledge and documentation supporting the grade
of rebar, let me know and I'll dig out the specs and other particulars.
Incidentally, the "Ufer" ground is a bargain in the search for lighting
>Also, are the J-bolts supposed to be wired to the rebar cage? It doesn't
>seem feasible, because the locations of the vertical sections of the J-bolts
>won't exactly touch the rebar cage... so, are the J-bolts simply suspended
>in the concrete?
I didn't weld the tower legs to the rebar because I didn't wish to
disrupt the galvanize on them. However, I brought three electrodes from
the rebar cage up near each leg and grounded the tower legs to those
electrodes and to the radial ground system, three radials extending from
the tower base for 32' with 2 ground rods on each, with cad-welded
connections to the rebar electrodes and to the ground rods. I prefer to
dissipate as much lighting energy as possible in the tower base and its
radials. Some sources recommend more radials. I'm not discussing RF
radials, needed if you wish to use the tower as a vertical antenna on
the low bands. I'm just providing a lightning dissipation system.
>Also, the J-bolts I got from Heights are just over 5 feet long... is it OK
>to have the bottom curves of the "J's" sitting on the base of the 5-foot
>deep hole hole? Or should I dig deeper to fully encase the J-bottoms in the
It is necessary to keep at least 2" of concrete between the steel and
earth, for corrosion resistance. Concrete is basic or alkali, which
protects steel. However, the alkalinity leaches away through the joint
between concrete and steel whever the steel extends out of the concrete,
and will leach away, though much slower, through the concrete.
>Help will be appreciated.
I took pictures of my rebar cage and the whole installation. I'll send
them for processing and make them available to those who are interested.
73 de WO?W
>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.
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