Antenna Rotator Problems

The big beam has been freewheeling for nearly a month. I finally cranked the thing down and took a look. Feedling is broken and the rotator sounds like it has marbles rolling around inside it.

The rotator is an Alliance HD-73. I had always thought it was much better than the CDE AR-22 but upon investigation the HD-73 can only handle a wind load of 10sq feet. Most ham rotators do 15sq feet or more.

Before the misshap I had trouble keeping the beam aligned to the rotator box indicator. At one time that problem was due to a missaligned gear that was driving the pot in the rotator. The HD-73 uses a potentiomemter inside the rotator to vary the voltage to a meter inside the control box. Well, this time the pot was just fine. The missalignment was due to the pipe mast slipping in the rotator coupling. So, I drilled a hole through the clamp and into the pipe. I threaded the hole in the pipe and screwed in a big bolt. Sucker would not slip anymore.

The HD-73 does not provide any sort of breaking to the mast other than the inertia of the geared motor mechanism. After the mast was not allowed to slip anymore, the force of t he wind stripped out the gears in the rotator. So much for avoiding slippage. I guess maybe the KT-34 was a little too much, or maybe the rotor was a little too light. There was no downward force on the rotor. A side saddle mount to the mast included a thrust bearing that bore the weight of the antenna.

So now that mast is tilted over and the beam removed, I can concentrate on repair.

I have a 50 foot tilt over. The tilting over part is drill stem pipe. The pipe is hinged at the 20 foot mark to a plate that is supported on the top of two sections of rohn tower. Been using that since the early 70’s of the last century.

Once I had the mast tilted over I tied it down so that if we did have storms there would not be any more damage. We did have storms but the only damage was due to my forgetting the mast was tied down before trying to raise it. I wondered why it took such a strain. Before I figured out what was going on, I ended up with a bent mast.

Tried to bend it back. No way that was going to work without risking pulling the tower sections out of the ground. So now I am having to engineed a way to remove the mast entirely so that I can cut the bent section out of the drill stem and weld it all back together after reinforcing the pipe above the 25 foot level.

The first 25 feet of pipe is 3 inch. The rest is 2.5 inch. It was 2.5 inch that bent.

Took a look at repairing the rotator. Found a fellow who does that. He also sells rotators. Wants close to 500 bucks for a new HD-73. Wants 60 bucks plus parts and shipping to repair a wrecked HD-73. That is shipping both ways and I figure one way was going to be around 20 bucks. So we are looking at 60+20+20+60(?) or more. Possibly close to 200 or better for repair.

Panasonic has a brand new rotator with twice the wind load capacity of the HD-73 for 300 bucks.

Unfotunately in this part of the country a wind load capacity of even 20 sq feet is inconsequential. We get storms with straight-line winds approaching. 90mph. God help you if you get brushed by a tornado. So it really does not matter that I ended up with a used AR-22. It will work. There is not downward force since the thrust bearing takes up the strain. And now I no longer pin the mast to the rotator so slippage is possible. What I really need is a very good braking mechanism to hold the pipe mast from turning in the wind. Of couse I know if I had that, It would just shell out the rotator when I froget to release the brake.

I have two old AR-22s. The AR-22s use two rows of ball bearings to support the rotating part against the non rotating part. But there are only six bearings on the top and six on the bottom. Those six are held spaced evenly around the perimeter by a band with spacers to keep the marbles in place.

The HD-73 had a full course of ball bearings top and bottom. I salvaged the balls out of the HD-73 and installed them in to one of the AR-22 rotators. The AR-22 with the extra balls will go on my auxilliary mast which will serve to hold a two meter beam and a multiband High frequency HF Moxon.

The remaining AR-22 will be used in the side saddle mount on the main tilt-over. It is going to be a 20 meter Moxon.

Both AR-22 rotators and their control boxes needed work. Both these rotators are four wire with really cheap screw connections in the base of the rotators. To prevent the screws coming loose with use, I decided to remove the screws entirely and solder the roator wire connections into the holes left by the screws.

As predictable the AC capacitors in both control boxes had aged ungracefully and need replacement. The replacement calls for a 120 to 150 mfd 50 volt AC capacitor. I did not have one of those. I did have a couple of 120mfds at 50 volt DC which when hooked back to beack. Minus to minus with the plus leads going to the old capacitor connections after the old capacitor is removed. That worked.

Caution, don’t install larger caps or caps of much smaller value. That will not work. I initially installed two 560mfd caps figuring that if 120mfd is good, 560 would be more good. Trouble was it was no good. I finally got the thing to work well by connecting a 120mfd and a 200mfd back to back.

Another thing that allows better preformance is clean and well lubringcated gear mechanisms inside the rotator. After cleaning and lubricating, both rotators functioned much better.

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