Even though J-Pole is a 'ground independent' antenna, it is often a good idea to ground it, to give a good reference point, to identify where the feedline ends and where the antenna begins. There are some argument for grounding the antenna, if nothing other than lightening hit immunity. There are, a few geeks who are ultimately disturbed by the presence of mast current, and if you are one of those, then please, go ground it. I believe one of the reasons this debate continued for such a long time is that it really didn’t make much difference at practical level, so neither side can win. Depending on magnitude of the leak, it's almost as bad as common mode current in the outer conductor of the coax feedline.įortunately, when you talk about 2m / 440 antenna, this imbalance can be expected to be small and hence it doesn't matter for most cases. There is always some factors creeping in to break that balance, so you can expect some current flowing through the bottom of the stub to the support mast (assuming it's metal). Above explanation is true as far as idealistic case is concerned. Hence the “bottom” of the stub is a neutral point, it really doesn’t matter if you ground it or not.ĬAUTION! As with many of my writings, I'm talking in practicality. The coax feed line connects to it slightly above the bend, locating the point where the impedance is about 50 ohm. There is no current flowing in/out of there if anything is connected. The Total length of the stub is about 1/4 wave length, and the bottom is the low impedance (virtual 0v) point. After some studying on the subject, I personally conclude this: “It doesn’t matter”.Īs I mentioned in the last blog (“V.UHF Dual Band J-Pole Antenna”), J-Pole is a half wave vertical dipole with stub match at the bottom. One of the big debatea about this antenna is whether to ground it through the support mast, or isolate it. Recently, I found someone studied it much further than I care to do, and concluded it performs pretty much the same as the normal J-Pole it just costs extra material to build ( Slim-Jim vs.

That antenna seems to have a cult following, so I'm not going to discuss much on the subject, but you can Google it to find all the wonderful praise about superior performance. Slim-Jim antenna doesn't help those issues.

For example, confuses this antenna with Zepp antenna, an end-fed wire antenna, which J-pole may have its conceptual origin but they are not the same thing. HF Band J-Pole Antenna (or NOT!) W6SI Blog Page (Entry 9)ĭespite the long history and popularity of this antenna, there seem to be a lot of confusion about what this is and how it works.

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