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More Unexplained A3 Balun Jumper Defects

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WB0VHB, Feb 24, 2021.

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  1. WB0VHB

    WB0VHB Ham Member QRZ Page

    Last Fall I rebuilt a Cushcraft A3 and used a Balun Designs model 1115. Checked tuning on the ground with an antenna analyzer and several days later lifted it in place on a 40' tower.

    I noticed intermittent operation and extremely high reflected power. Climbing the tower, I gently pulled on the balun to driven element jumpers. Both wires pulled out of the crimp connectors. Closer inspection shows the wires burnt off the connectors. Two of the pictures attached show what I found.

    I only run 100 watts and there weren't any thunderstorms during that time. Wrote it off as one of those unexplained things that happen with antennas, replaced the jumpers and continued to enjoy the antenna.

    About 2 weeks ago I once again experienced extremely high reflected power and receive signals would go from S9 to S1 intermittently. With wind chills at -10F, climbing the tower would have to wait. Yesterday was 45F and calm so up the tower I went. This time I found one of the crimp connectors broken in two! No signs of burning, just broken this time. The jumpers are located so that they can not come in contact with anything when the antenna is rotated, there's plenty of clearance.

    I supposed these failures could just be unrelated coincidences. Anyone with similar failures?

    Attached Files:

  2. KF5FEI

    KF5FEI Ham Member QRZ Page

    Soldered crimp connectors will break like that, when flexed. Need to buy quality connectors, use quality crimpers, and use heat-shrink for extra flex protection.
  3. WB0VHB

    WB0VHB Ham Member QRZ Page

    There wasn't any flexing done to this connector. It can't come in contact with anything when the antenna is turned. This is a quality connector and crimper. I use these connectors and crimpers in public safety equipment installations for many years and have never had a failure like this.

    As a test, I took a new connector and soldered a wire to it. Then clamped it in a vise. It took 13 twists back and forth before breaking.
  4. W1VT

    W1VT Ham Member QRZ Page

    Yes, I've seen this with my RX loops and soldered wire connections that are exposed to the weather. Fortunately they are close to the ground and easy to fix.

    I've been working on better techniques but I don't have any that are ready for publication.

    Zak W1VT
    Last edited: Feb 24, 2021
  5. KH6AQ

    KH6AQ Ham Member QRZ Page

    I don't bother to crimp most lugs and use solder only.
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Maybe I'm looking at the images wrongly but it looks to me like in the first two, the wire itself burned and broke while in the second two it appears like the terminal metal actually broke -- two different kinds of failures, but all at the same connection points?

    Is that what it shows?
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Rethinking this, it occurs to me that the one constant that maybe hasn't been explored is the A3 driven element, itself.

    If one of the DE insulators breaks down and shorts to the boom, or one of the DE traps is intermittent, or one of the DE tubing clamps isn't providing excellent electrical contact between tubing sections...any of those could cause a huge bump in current at the balun which might exceed the jumper wire rating. You'd think that should shut down your transmitter rather instantly, especially with a modern 100W transceiver, all of which have foldback protection against big mismatches, but maybe something really weird is going on.
  8. WB0VHB

    WB0VHB Ham Member QRZ Page

    Yes, 2 different kinds of failures to the jumpers. That's what baffles me.

    The jumpers that burnt last Fall originally had heat shrink tubing over them. They looked OK at first inspection but when I gently pulled on one of the wires, it pulled right out of the heat shrink tubing as did the other jumper. Yes, the latest failure is the crimp connector broke in two. Hard to see in the picture but under a magnifying lens, the break looks similar what cast iron looks like when it breaks because of it's brittle nature. The broken edges are rough.

    If this continues, I will have to consider a fold over or crank down tower so I don't have to keep climbing.
  9. K3EO

    K3EO Ham Member QRZ Page

    At -10F temperatures, solder joints are probably more prone to failures, especially under vibration. Over time, wind vibrations and temperature cycling can cause stress fractures.
    The shearing of the lug definitely looks like there was some stress involved.
    Another things to consider: What kind of solder did you use and is it rated for that environment?
    Several years ago one of my suppliers (inadvertently?) used plumbers solder instead of the normal tin/lead electrical solder. Fortunately, our test technician noticed the discolored joints and we had the supplier rework all of the suspected joints.
  10. K1VW

    K1VW Premium Subscriber QRZ Page

    I suspect you are doing everything right, just you have a bit of flex going on up there when the wind blows, or jerky vibration when rotating. I would remove the plastic insulator from the lug, and cover it with multiple layers of heat shrink tubing, that helps reduce flex. Then use something to mechanically support or splint it so it’s less likely to move, like maybe a piece of rubber tubing, run along side it, and tape it all up, so the tubing takes the mechanical stress instead of the electrical connections.

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