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RB wrote:
I've recently put up a 140' dipole fed with ladderline. My tuner is separate from my rig, and is an unbalanced unit. So, I use a balun on the tuner output to hook the ladderline to. I've been told that I should have a voltage balun in this application. I was surprised to hear this, as I expected to hear use a current balun. Is the voltage balun the right one for this application? Only if you want your feedline currents to be unbalanced. Your antenna is a lot like the one described on my web page below that uses a 1:1 choke-current-balun and needs no conventional tuner, the most efficient configuration I could come up with. As can be seen from the current maximum point graph on my web page, ~100 feet is a good compromise length for the ladder-line for such an antenna. A lot of hams will tell you to throw up a random length of ladder-line and feed it through a 4:1 voltage balun. That's usually not good advice and often results in a poor balun function on one or more bands. If one doesn't know approximately what impedance is being seen by the balun, one cannot predict if it will function or not. The free version of EZNEC can predict the approximate impedance seen by the balun. www.eznec.com -- 73, Cecil http://www.qsl.net/w5dxp/notuner.htm |
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