Off Center Fed Dipoles with hybrid balun

Started by Lamewolf, March 08, 2016, 07:53:23 AM

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Lamewolf

Just built a new off center fed dipole for 6 thru 80 meter operation.  Nothing special about the antenna since its the standard 45' - 90' split to cover 80, 40, 20, 17, 12, 10 and 6 meters, but since they are notorious for common mode current on 80 meters, I decided to do a hybrid balun on this one to tame the CMC (common mode current).  The balun is a 4:1 Ruthroff voltage balun wound on an FT240-61 core with 12 bifilar windings, and that is connected to the feed line through a 1:1 choke that is wound with 18 turns of Teflon insulated coax similar to RG174 coax rated at 100 watts on an FT140-43 core which equates out to about 6000 ohms of choking impedance to keep RF off the coax shield.  But cores are mounted in the same box to which the antenna is connected to by stainless steel eyebolts.  The 1:1 choke will limit me to 100 watts but I never run more than that anyway, but with the choke in place I should get radiation form the antenna only and not the feed line which also results in more accurate swr readings.  Will hoist it up sometime this weekend to give it a try and will post results here.

cockpitbob

Sounds like a really nice antenna.  Where did you learn about it?

Lamewolf

Quote from: cockpitbob on March 08, 2016, 08:25:37 AM
Sounds like a really nice antenna.  Where did you learn about it?

Through readings from this website: http://www.dj0ip.de/balun-stuff/baluns-for-tuners/balun-truth-table/

This guy knows his stuff and has lots of info on his site !