A -NEW- Unadilla W2DU choke balun and 2 days of rain...

[N9NLU]

Just over a month ago, I purchased at AES Milwaukee a Unadilla W2DU HF Dipole 1:1 " Maxi-Balun" Choke balun for a 75m inverted vee dipole that I was constructing.

Late last week, I finally got around to installing the W2DU balun at 65ft and fed it with 100ft with of new Belden 9913F7 coax. Then the rain came in Saturday and Sunday with plenty of wind. Saturday evening I installed the connector in the shack and checked the antenna ... BAD! Thinking I might have used too much heat on the connector in the shack, I clipped it off and checked resistance of the coax. It was shorted somewhere still, not a dead short, it was giving me something like 400-500 Meg ohms.

Monday I took down the antenna, struggled with pealing off the electrical tape and butyl rubber sealant then unscrewed the pl-259 connector. Water dripped out of the balun and connector. Now I know It was not my sealing job, I've done this hundreds of times with heliax fittings, using the same Andrew Corp waterproofing kit supplies as I used on this connector.

I then checked the W2DU choke balun for resistance, there should be none since its just a section of coax with ferrite beads over it. It was giving me 60 Meg ohms outside in the cold. I made the educated guess that water leaked in through one or more of the three eyebolts at the top of the balun. I then e-mailed Unadilla about this problem of water leaking into the balun and then ruining into my new coax from inside the balun. Later that evening, I checked it again and it was giving me 30 meg ohms on the bench. Today I checked it again no resistance. I still have not heard anything from anyone at Unadilla - very nice customer service - I think NOT! Since I doubt I would be able to return it to AES because its an antenna component and their policy is No returns on coax, antennas etc... I sawed open the thin walled PVC housing which had ABS plastic caps.

It is constructed of a section of RG-303/U coax with 49 ferrite beads over it (I read somewhere its is constructed using 50 beads). A round-ish piece of "fishpaper" (http://en.wikipedia.org/wiki/Fishpaper) was used in the middle of the string of beads to keep it centered in the tube. A rubber feed through grommet holds the beads in place at the top and a pair of rubber washers hold the beads in place at the bottom along with the shield of the coax bent into an L shape to keep the rubber washers from sliding down. Unadilla's W2DU "static dissipation device" is at the top of the tube and consists of using the 3 threaded u-bolt ends in close proximity to each other -WITHOUT- conical ends to help induce a spark discharge at a lower threshold. They just were the regular ol ends of any ol threaded eye-bolt. This discharge device would only work IF the SHIELD of the coax was well grounded because the device relies on the shield conductor to conduct the voltage down to - hopefully an outside grounding point and not the grounding point on the radio itself. These eyebolt ends formed about a 1/16" gap. Not much of a static dissipator. There was ABSOLUTELY --NO-- SEALANT on or around the eyebolts where they come through the ABS plastic cap and no sealant on the open ends of the RG-303/u coax used. Not even some cheap hot glue... nothing! There is where the water came through - the unsealed eyebolts. In fact, the fishpaper was soggy and water still was dripping out from between the ferrite beads when I was moving it around. The resistance I measured at the balun's so-239 came from water dripping onto the open ends of the coax in the balun.

So, between the obvious poor design and construction, and then the lack of communications / customer service, I cannot recommend to anyone, the purchase or use of this Unadilla W2DU "Maxi-Balun" for any antenna that will be outdoors. Got 130ft+ of attic space, you could use this balun for an indoor 75 meter antenna - very un-practical. In fact, with the lack of customer service, I would stay clear of Unadilla, period.

So, the $31 Unadilla W2DU HF Dipole 1:1 Maxi-Balun was a total waste of money which subsequently rendered the new, 100ft of Belden 9913F7, $149.98 at AES Milwaukee, into a pile of scrap in only 2 days of being installed. Who knows how far the water migrated down the inside of the coax.

Take warning if you are thinking of purchasing or using one of these or any Unadilla products. At minimum, you will need to seal the outside hardware if you are going to use one because Unadilla doesn't seal it. "Made by HAMS, Andover MA", the label says. Any ham with the knowledge that water is conductive would know to seal where ever water could run in via gravity or blow in etc... Unadilla decided to cut that corner and omit the sealant to save a few pennies in constructing each balun.


Dave Schmidt
N9NLU
Kewaskum, WI