Cushcraft A4 Repair (Fail!)
Cushcraft A4 Repair (Fail!)
Shortly after I had repaired my Cushcraft A4 tribander beam the last time, I noticed that it appeared to have a loose connection somewhere. Especially when the wind was blowing, I would hear something that sounded a little like static crashes, or pops in the receiver. This was especially noticeable on 20 meters, but was apparent on all bands.
About a year ago, I climbed up and removed the short coax that made up the balun, which connected to the long feedline on one end, and the beam on the other. It was very weather beaten, and looked to have poor connections at the antenna end.
After examining the coax, I decided to just build a new one. This just involved installing some terminal ends on one end of a new piece of coax, and a PL-259 connector with a barrel at the other end.
After building and testing the balun in the shop, I climbed back up and installed it. I cleaned the screws that connect it to the beam antenna, and the PL-259 on the end of the feedline. After hooking everything up, I taped the connections and applied liquid tape to protect the open terminal connections at the beam.
With great hope, I dismounted the tower and went in the shack to do an end-to-end check. Alas, the popping noise persisted. At this point, I was suspecting a loose connection in one or more of the traps, and decided to wait until later to bring the entire beam down and try to repair it. I also noticed that my Yaesu Rotator had stopped working for the second time. I thought this might be broken gears, as I had experienced before with this rotator. The rotator would also have to be brought down off the tower for repairs. Thinking that the rotor might be a little under-sized for the A4 beam, I ordered a Hy-Gain Ham IV rotator to replace it.
In early May, my friend John, WB0WHO came down from Nebraska to visit. I put him to work as a ground man, while we worked to lower the 37 lb Cushcraft A4 to the ground.
First, we built a gin-pole, to provide a pully at the top, away from the edge of the tower. The hook on the bottom of the Gin-Pole rests in the cross bracing on the side of the tower, then the top is held against the tower with bungee cords and rope.
Then, we mounted a boat trailer winch to a piece of 2×6 board which we strapped to the lower end of the tower.
I climbed up the tower and ran a length of rope through the pulley, and attached to to the antenna. The other end of the rope was attached to the end of the cable that came with the boat winch. Tension was placed on the antenna, and hardware was loosened at the top. I lifted the A4 off of the mast, and twisted it around so that it laid beside the tower side, without touching. Then John slowly winched the antenna down off the tower, as I helped guide it in avoiding obstacles, such as our house roof and pool fence, on the way down. After that was down, the rotator was lowered to the ground by rope.
Once the antenna was on the ground, we mounted it on a short mast, and set about testing it.
I sat in the shack and listened to 20 meters, while John walked around and tapped the antenna with a stick at all of the element joints. We were able to duplicate the problem on the ground, and proceeded to do repairs as we continued testing.
The problem seemed to be associated with the driven element, particularly on one side. We found the capacity hats for 40 meters were loose, but this did not solve the problem.
We removed one half of an element at a time, and set about taking it apart, cleaning the joints with green scotch brite pads, and examining the traps. If the traps sounded like there were loose pieces or had decayed insulators on the ends, they were taken apart, tightened up and reassembled. We put the best looking insulators on the outer ends of the traps and sealed all of the end caps with Scotch Electrical Tape. When a complete element was rebuilt, we reinstalled it back on the boom, after cleaning the boom clamps with a wire brush.
After completing the Director and Driven elements, we had found a couple of traps with loose connections, and felt confident that we had solved the problem. John set about tapping the elements again, and again, I heard the popping sounds on the same side of the driven element that we had just rebuilt. We had not rebuilt all of the traps, as those that seemed solid were just cleaned and reinstalled. But it appeared that there were more problems with them.
At this point, because of the poor condition of the insulators in the traps, I decided that a new beam would be the best solution. I didn’t want to waste more time rebuilding all of the traps (something like 12 of them), only to find that it would break again after re-installation of the antenna on the tower. I looked into replacing the traps with new ones from Cushcraft (MFJ), but an examination of the assembly manuals showed that there were some changes over the years, and I wasn’t certain that the new traps would be appropriate for the old antenna.
So we marked all of the pieces with a sharpie, covered the labels with packing tape, and dissembled the beam, packing it into several bundles (director, driven, reflector and 10-meter elements, boom and hardware). Perhaps someone will need some parts that I can provide in the future. If not, there is a lot of aluminum to build new antennas with.
An examination of the Yaesu G-450 rotator controller box showed a burned mark under one of the terminals on the back. I suspect that it had experienced a pulse from a nearby lightning strike, and was probably the reason for the failure of the rotator. I will attempt a repair down the road on that.
So, after researching some new beams, and getting some recommendations from friends, I decided to order the NA4RR Hex beam as my new antenna. It covers all of the ham bands from 20 meters through 6 meters, including the WARC bands. It is light weight and should be easy to install. We will see in my future post about its installation.
Migrated Comments:
July 13th, 2017 at 2:36 am
Do you have the original A-4 manual not the A-4S? I the original A-4 and trying to identify the traps,the markings have been lost due to weather. I think the A-4e has different traps?
73 Larry DU3LA
July 13th, 2017 at 7:32 am
Sorry, Larry. My manual is for the A4-S.
December 4th, 2018 at 2:37 pm
I have an earlier used A4and the trap designation at least for the 10 meter traps was definitely different from the designation that the new A4S manual shows. The only marking was on the inside of the trap that was thankfully marked with a magic marker apparently by an earlier owner as Cushcraft is too cheap to mark their traps with any kind of permanent marker or permanently engrave the trap cover. Been having fun determining which trap goes where as the tip to use a grid dim meter is ridiculous as the resonance points are too close to reliably separate so a network analyzer is the only option other than playing musical traps.
December 4th, 2018 at 2:42 pm
I have an earlier used A4and the trap designation at least for the 10 meter traps was definitely different from the designation that the new A4S manual shows. The only marking was on the inside of the trap that was thankfully marked with a magic marker apparently by an earlier owner as Cushcraft is too cheap to mark their traps with any kind of permanent marker or permanently engrave the trap cover. The screw holding the trap to the metal trap cover should always face the boom. Got my traps mixed up cleaning the and been having fun determining which trap goes where as the tip to use a grid dim meter is ridiculous as the resonance points are too close to reliably separate, so a network analyzer is the only option other than playing musical traps.