Off Center Fed Dipole

Started by Lamewolf, July 03, 2020, 09:39:56 pm

Previous topic - Next topic


Been away for a while and just got back on tonight, so I thought I would share the antenna I have been experimenting with that seems to work gangbusters and most places without a tuner.  Its an off center fed dipole that covers 80, 40, 20, 17, 12, 10, and 6 meters.  The initial resonance is set to 3.450 mhz (yes, below the band edge) to get the bands 40 and up at resonance.  But to move 80 meter resonance up the band without changing the other bands you put a capacitance between the balun and the long leg of the antenna.  I operate around 3.825 mhz and two 180pf 5KV caps in series gives me around 95pf @ 10KV and gets my swr on 3.825 a 1.2:1 for no tuner operation.  2:1 swr points on 80 meters starts at 3.745 mhz and extends to the top of the band where its only 1.8:1.  Below 3.745 I do use a manual tuner if I'm using the amp, but if I'm running barefoot, the tuner in my Icom 7300 matches it just fine.  40 and 20 meters needs no tuner at all, but 17 meters is a little above 2:1 - around 2.3:1, so I use a tuner there too. 12 meters needs no tuner at all, and 10 is usable from 29.0 to 28.680 without a tuner, and six meters is a bot above 2:1 but again, the tuner in the 7300 takes care of that no problem.  On WSPR mode running only 3 watts, I'm being heard all over the US and Europe with it.  The balun is a hybrid balun  that contains a 4:1 Ruthroff voltage balun to convert the antennas feedpoint impedance of around 200 ohms to 50 ohms, then it has a 1:1 Guanella current balun between the 4:1 and the coax to block common mode currents from the outside of the coax shield.  Hope some of you decide to try it, its been a real success here and fun to build !