|Installing an MA-40 Light Duty Tower|
The US Tower MA-40 is a free-standing, telescoping, tilt-over light duty tower suitable for a small yagi or quad. It will crank down to 21 ft. 6 in. and extend to 40 ft. I came across this one used and reasonably priced. Getting it home was another matter. Jack Sproat, W4JS, recommended a boat trailer and that worked out very well. I rented one in Sarasota and Konrad Owens, WA3RRS, made the round trip with me to Punta Gorda. Many thanks, this is definitely not a one-man job! The boat trailer has center rollers and a winch which greatly simplified loading the tower. Unloading it was much more difficult. We escaped injury and successfully left the tower sections on jack stands in my side yard where it would sit for quite a while as the base installation proceeded and the tower was refurbished.
The base spec for the MA-40 calls for a 3 ft. square by 5 ft. deep hole. This is not me in the hole but Bill Shanley, a local handy-man who expertly dug this hole after cutting through the patio. The hole needed to be dug with minimal disturbance to the surrounding earth. The wires were re-routed.
Not too bad for a first attempt at building a rebar cage. Actually it's pretty easy. The cage has to be kept within the concrete by 3 inches on all sides. This includes standing it on those orange supports to keep it 3 in. off the bottom of the hole. After each one of the first few loads of concrete were poured the cage was jostled about to keep it centered. The cage must also be kept well clear of the base bolts which were imbedded in the concrete late in the pouring process.
This is the completed pour. After the concrete dried a little, it was covered with mulch and plastic sheeting to keep it moist during the curing, and to keep the sun off. I wet down the mulch every other day or so as the concrete cured for the next 28 days. It actually does take concrete 28 days to reach 100% strength. This is 5000+ psi concrete with fiber in it to increase strength. Having it delivered turned out to be far more cost-effective than mixing it myself and probably a much better mix. The bolts are 36" x 3/4" #10 galvanized with nuts and washers at the bottom end and another set about a foot up from the bottom. The plywood template is matched to the tower base and the template was carefully aligned so that the bolts would be properly placed. Where the tower had to be installed did not leave much margin for error.
The refurbished base installed on the bolts. The base had a coating of surface rust which was removed by some light sandblasting and then it was primed and painted. All the hardware was replaced as well as the winch and cable. Some areas were caulked to help keep water from collecting. The pulley was removed and greased as well.
A cradle was built to trolley the mast over to the base. Thanks to Bob Avrutik, N1RA, and my dad, John, we safely got the mast maneuvered into place. Bob insisted the trolley have a proper license plate which I just happened to have lying around left over from my old call sign.
The main mast is secured to the base with a 1/2 in. galvanized steel bolt. Bob and I fought with this for a while to get it lined up only to find out that I had initially placed the mast upside-down. The tower winch has to face the opposite way from the base or the mast will not go completely vertical. There is not enough room between the base raising post and the mast for the Fulton K-1550, 1500 lb. winch which was a little larger than the original. The photo shows the mast in its corrected position.
The question is: Will the mast clear the gutter?
There are actually a couple more inches of margin than it appears.
After the mast is installed and plumb and the bolts are all locked down, the underside of the base plate has to be back-filled with minimum 6,000+ psi, non-shrink grout. After mixing the grout to a "plastic" consistency you have about 15 minutes to work it into place.
The mast is grounded to a 3/4" by 10 ft. copper pipe and tied into the rest of the ground system.
TARC members helped out with this project throughout and also patiently answered many questions. Thank you all!