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Are you having RF problems in the shack since you put up your HF vertical antenna? This is a common problem with an easy solution. RF energy traveling into your shack on the outside of the coax feed line causes this problem. The solution is adding an "ugly" 1:1 Balun in the coax to choke off the RF energy before it enters your shack.

So what's an "ugly" Balun? Nothing more than a few turns of the coax forming a coil. Don't scramble the turns; they must be side by side for the coax Balun to operate properly. 5 turns or more will be enough for 80-meters and up. Use caution not to coil the coax so tight that it causes the inside conductor to merge into the shield shorting it out. 4" PVC pipe coupler works well and it's cheap. Normally a 1:1 Balun would consist of multiple turns of three wires on a coil form and the simple coax Balun is also multiple turns of three wires when coiled, the center conductor, the inside of the coax shield, and the outside of the coax shield. Now your asking how this could possibly work. RF energy flows on the conductor and not in the conductor. This is the reason silver-plating or copper-clad steel works so well. The RF energy only penetrates the conductor slightly and for plated parts the RF flows entirely in the silver or copper plating and almost never in the conductor below it. In the case of coax this property separates the RF flowing inside the coax from the RF flowing on the outside of the coax.

We can use this problem to an advantage by careful placement of the "ugly" Balun. Most of us would think we would want that Balun at the base of the vertical and try and prevent all RF from flowing on the outside of the coax. In reality this is the worst place you could put it! Why? Simply use the outside of the coax as another radial. Putting the Balun at the base of the antenna would choke off the RF but the vertical element would simply put it there again. The Place to put the Balun would be 1/4-wavelength from the feed point of the vertical on the lowest band the antenna is capable of operating on. If your coax run is 1/2-wavelength or more you will want to place a Balun at each 1/4-wavelength point. You will also want to put a Balun on the feed line just before it enters the shack.

The formula for figuring out where the Balun should be placed is simple. 234 / frequency in MHz * the velocity factor of the coax = length in feet. An example is a Butternut HF6V 80 through 10 meter vertical. As the antenna is capable of operating on 80 meters simply input 234 divided by 3.5 times .75 would equal 50.14 feet assuming your using modern foam type coax with a velocity factor of .75. The HF6V uses a length of 75-ohm coax as a matching transformer. Simply ignore the velocity factor if different from the 50-ohm coax and measure 50.14 feet from the feed point of the vertical for the proper place to coil the coax forming the 1:1 Balun. If your feed line is shorter than a 1/4-wavelength on the lowest band the antenna is capable of operating on, place the Balun on the next highest band where the coax would be longer than 1/4-wavelength. This should cure RF problems associated with RF flowing into your shack on the outside of the verticals feed point.

N4ZOU