On 1/31/2017 2:16 PM, Fred Jensen wrote: > A bal-un is a transformer. Technically, it has two windings on a > ferromagnetic core material which for RF is typically some flavor of > ferrite, usually in the form of a toroid.
Most common baluns are *not transformers* as the energy does not pass solely from input to output by magnetic coupling. In fact, I would hazard a guess that *none* of the devices advertised/sold as baluns are transformers. Yes, many of the inexpensive 4:1 "baluns" - the voltage type (auto-transformer) baluns - may qualify due to the magnetic coupling between windings but they are *not* baluns in that they do not provide a balanced to unbalanced transformation (they are, in your terms an "un-un").
In the classic case, a balanced load [e.g. center of a half-wave wire] becomes unbalanced [coax, shield grounded] by the bal-un.
Again, NO! The balanced load is not "unbalanced" by the balun. A properly designed balun *keeps the system balanced* by preventing current from flowing on the "third wire" (the *outside* of the coax) which would otherwise "unbalance" the system. Due to skin effect, a properly terminated coaxial cable is a three wire transmission line. The center conductor and *inside* of the shield form one circuit (which is "balanced" due to the laws of physics) and the *outside* of the shield carries "unbalanced" (or common mode) current due to any difference in potential between the ends of the cable or induced currents from external fields. 73, ... Joe, W4TV ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
