[OFARC] MFJ balun - learning moment

[Don Davis]

Hi to all,
Attached is a photo of a balun used on an MFJ 1836H cobweb antenna. I started building this antenna before the hurricane and quickly set it aside as the hurricane approached. I mounted it on a mast in the backyard about 6 feet up and proceeded to tune the 20-6m bands. At times I would get high SWR readings that I couldn't understand why. I was using several cheap RG -8 coax cables to obtain 18 feet from the antenna to the antenna analyzer. By wiggling the connectors, the readings would go down and I could tune the individual bands. 
After tuning the bands, I place the antenna on a mast connected to the house and raised it up about 16 feet above ground. As a precaution, the 20M band was checked again and the readings were way off as from before. Blaming the cheap cables, I went to ABR Industries and Shannon made me a cable about 20 feet long. Testing with the new cable, the SWR was low as expected. I moved the cable by twisting it and the SWR reading bounced around to high values. I lowered the antenna and inspected the coax connector on the balun and it pulled away from its cable. The crimp was loose, and the center conductor was poorly soldered.
I proceeded with the balun back to ABR to see if Shannon could apply a new connector. On her inspection, she noted that the ferrite beads on the cable were spaced from each other with ty wraps and they were not connected together using heat shrink tubing. I asked why did MFJ allow the ferrite beads to be spaced? Her partner, Chuck, indicated it changes the impedance and they should be connected together for a high impedance. Note the new connector and the ferrite beads connected together with heat shrink. Nice learning experience!
Don KI5WWD

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