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April 27th 07, 11:53 PM posted to rec.radio.amateur.antenna

Owen Duffy Owen Duffy is offline

Owen Duffy is offline

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First recorded activity by RadioBanter: Dec 2006

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Impedance transformation question

wrote in news:1177712640.116329.181210
@o40g2000prh.googlegroups.com:

Hi,

If EZNEC reports a source impedance for a balanced antenna, such as
a loop, of R+-jX ohms, and I am trying to match the antenna to the
line: I am using a Smith Chart program that is unbalanced i.e.
everything is respect to ground. Question is, what impedance do I
enter into the program such that I will get the correct matching
solution for the balanced antenna? I have used this program numerous
times and it works well for verticals, mobiles, and other unbalanced
antennas. Thanks.

Gary,

The impedance transformation is unaffected by whether the load is
balanced or unbalanced. The Smith chart solution does not depend on
balance or not, nor does the underlying maths.

Having said that, if you intend including a balun, you could treat it
simply as an ideal n:1 impedance ratio transformer, dividing the load
impedance at the appropriate point by n... though that may splitting your
Smith chart solution into two parts each side of the transformer (if n!=
1). Some Smith chart software allows specification of a transformer as a
system element, so it is real easy and all displayed on one map.

If you don't want to treat the balun as ideal, my view is that you really
need to include the balun and a path for common mode currents in your NEC
model, because they are actually couped to the radiator and form part of
the system load.

Owen

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