Excellent explanation, Joe.
Thanks,
matt W6NIA
On 1/31/2017 12:12 PM, Joe Subich, W4TV wrote:
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:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
--
Always store beer in a dark place. - R. Heinlein
Matt Zilmer, W6NIA
[Shiraz]
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
