Easy One-Man Installation of a Steppir 4 Element Beam

A Swivel Boom to Mast Plate makes the project possible.
 

The swivel boom to mast plate will allow me install a 4 element SteppIR atop my 200 foot Rohn 65 tower by myself. It consists of two 5 inch by 10 inch 3/8 inch thick 6061-T6 aluminum plates with a 1 inch stainless steel hinge pin passing through the centers of the plates.  The front side of the pin has a larger boss to seat against the plate, the other side has a hole for a large stainless cotter pin. The two plates are held 1 inch apart by a spacer made of a piece of 4 inch solid aluminum round stock. The purpose of the spacing is to allow room for the back side for the U bolts to clear each other as  the plates rotate. One plate has 2 inch U bolts for the mast, the other 2.5 inch U bolts for the boom. It will allow me to install the boom and element housings, then insert the fiberglass tubes with the boom vertical alongside the tower. When the elements on one side of the boom are completed a temporary weight will be hoisted to the top of the up side for balance, then the balanced boom  can be  be swiveled back horizontal with no effort. Rotate the mast 180 degrees and  the other side of the boom will come down against the tower.  When assembly is complete the temporary weight will be removed and the boom can be rotated horizontal and locked in place with four 3/8 inch stainless steel through bolts. A short pipe for the Phillystran support cables is affixed to the movable plate so that the boom truss assembly can swivel with the boom.  Two collars, one on each side of the plate,  insure that the boom will not shift position even if the U bolts are loose.  The swivel mount will make future maintenance and service very easy.  It will take only about five minutes to let either end of the boom down against the tower and make the elements available for maintenance or service.

To use a swivel bracket like this one your rotor cannot be centered in the tower, it must be offset on the side of tower so that the tower will not interfere when the boom is swiveled down.  I have built two mounting plates, one for the rotor and one for the top plate, that extend out away from the tower far enough that the boom will clear the legs on my tower when I rotate it down.  It also requires that the top approximately 16 feet of the tower is free of guy wires on two sides.  In my case I made provisions to quickly slack off two of the top Phillystran guys during assembly or maintenance.

This is not intended to be a construction article, just food for thought. I always use the materials that I have on hand and adapt the project to them when possible, and that was the case for this assembly.

Update 12/17/07! The antenna arrived December 10th. It has been set up, fully assembled and tested, and knocked back down for transport up the tower.  Each item has its own tower clip so that it can be temporarily stored atop the tower until needed. Each element pair is bridled together with a common tower clip. This clip will remain in place on the tower until the elements are fully installed. There is a picture below of the "kitted" antenna starting up the tower; more pictures will be posted soon.

12/28/07  Everything installed today except the element tubes, the 6 meter elements and the Phantom element. Sunset came too early! More pictures posted today.

12/29/07  Installed the elements and finished up the installation except for the control cable hookup. 3 more pictures posted.

Jim Frederick, W4LF

 


The U bolt cradles for the 2-inch mast are from an old Mosley Classic 33. The cradles for the
2-1/2 boom are milled from aluminum bar stock.  They attach to the plate with two 6-32 screws
to avoid having any more loose hardware atop the tower.

The two identical collars slip over the boom on each side of the boom plate to prevent the boom
from shifting before the U bolts are fully tightened. The other collar will be used on the mast. The other
3/4 inch hole in each plate were already drilled for a prior project and are not used.


Honest, I will remember to replace the tie wrap with a large cotter pin! The four through bolts
are shown in this picture.

 

Here are  pictures of my assembly temporarily mounted on a spare tower section that was available for testing.  Unfortunately, the whole assembly is pictured upside down. The pipe shown that goes through the cutout in the top plate is actually the Phillystran bridle support. Visualize this picture with the short pipe to the "up" side away from tower and the boom of the beam through the large 2.5 inch U bolts. Now the boom can swivel down into the cutout in the top plate. The EHU's will be to the outside, toward the viewer in this picture. To access the other end of the boom level it, rotate 180 degrees, and it comes down in the opposite cutout in the top plate.

 

For this system to work the rotor must be outside the line of the tower. It cannot be mounted inside the tower. Note that the rotor plate was cut to allow the boom to pass to either side when it is rotated down. The mast is 2-inch 6061-T6 .375 inch wall tubing except for a 6-inch socket at the top. An 8 foot long 1-7/8 double wall pipe slips into the socket and extends up for my 2 Meter beam.

One of my other projects is what I call a DivertIR.  It is a relay box that completely disconnects the SteppIR control box from the control cable for lightning protection. Because I live in the lightning belt of Central Florida I always unplug my Ham gear when not in use. When my ham  bench power goes down this box will switch the antenna cable to a separate power supply to provide holding current for the EHU motors.  This should prevent any possible movement of the tapes due to a lack of holding current. A timing circuit is used to ensure that the cable is re-connected to the SteppIR control box before the box can power up.  I also have two stage surge protection on each lead of the control cable. For anyone interested, the holding current in the SteppIR is 100 mA. Since the motor DC resistance is 15 ohms this results in 1.5 volts across each winding.  The holding current is DC, but the running current is effectively AC since it is pulsed. The motors draw about 430 mA when running, and mine have 28 volts across each winding using the optional 33 volt power supply. This was measured with 350 feet of cable in the line.

Here is a view of the "kitted" Steppir ready to go up the tower. The whole antenna is here, the boom, the support pipe and Phillystran supports, the elements, and a "Phantom" element which provides wind balance. Balancing the antenna greatly reduces the stress on the rotor and helps keep the mast clamps from slipping on the boom.  It is being pulled up with a Polaris utility vehicle. The pull rope comes down, then passes through a second pulley on the arm of the tractor. The white spot on the elements is padding to avoid scratching them.

 


Here is the "kit" ready to go up the tower. Everything went at once.


Transferring the antenna from the rope and pulley to the small winch used to pull it up to the mast                                    Stormie Burns Photo


It looks like I am waving, but actually I am running the winch lever. It is almost up over the tower      Stormie Burns Photo
in this picture. After 50 years of climbing towers this was a new experience - I am sitting inside the tower.


Success!  It is now in position, securely bolted to the mast and the bridle has been installed.                   Stormie Burns Photo
Time ran today so the elements will be installed tomorrow. They are stored out of harm's way, just below the bottom of
this picture. Either side of the boom will swivel all the way down tight against the tower face, so it will be easy to install
the elements.


This photo shows how the boom tips down. The bent pipe jutting out below the         Stormie Burns Photo
antenna is an old conduit that is being removed. The 2 Meter antenna that
will go 9 foot over the SteppIR can be seen hanging on the tower .

 


Finishing up all the little details. Notice the "Phantom" element that wind balances the antenna                                            Stormie Burns Photo 

                                                               


Here is a picture of my ground crew. She likes to chew on the utility vehicle.

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