On 8/12/2013 2:10 PM, JC N4IS wrote:
50/75 BALUN
Thanks for the detailed post, Carlos. BUT -- please let's use the right
words to describe things so that people understand what you're
describing and how it works. I strongly suspect that at least some of
those things you are calling a "balun" are really a simple transformer
-- that is, a primary and a secondary with magnetic coupling between
them, and probably on a ferrite or powdered iron core. If it's a
transformer, let's call it a transformer. Likewise, if we have a common
mode choke formed by winding a coil of the transmission line, it is a
common mode choke, not a "balun." Using the word "balun" confuses
things, because that word is used to describe at least a dozen very
different things that I know of.
When we use the word "balun," it's a magic box that few hams really
understand. When we use the right word, most hams have a chance of
understanding what it does in a circuit. :)
Yes, there are arrays of common mode chokes that can be used to
transform impedance, and there are transmission line transformers of
various sorts that can do that as well.
BTW -- your discussion of phasing between elements of an RX array causes
me to add an important post script to my advice that a perfect match is
not required. When ANY passive network is used to produce phase shift,
the source and termination impedances DO matter. The tricky part,
though, is knowing what the input Z of the RX is, and if you're doing
something like a phased array using phasing lines that end at the RX
input, it might be a good idea to actually measure input Z and the
antenna Zs with a VNA.
73, Jim K9YC
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Topband Reflector
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