"christofire" wrote in message
...

"John Smith" wrote in message
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Tad Danley wrote:
I have started to experiment with EZNEC and am modeling a couple of loop
antennas including some delta loops. I see references to hams using 4:1
baluns with these antennas, but the models I see show a feed point
impedance of roughly 100 ohms. I'm not sure how a 4:1 balun would
help - what am I missing?

Thanks and 73,

Tad Danley, K3TD

Tad:

A 2:1 construction of a "true" 2:1 balun is possible, however, driving a
100 ohm loop from 50 ohm coax does NOT require one--meaning, a 2:1 "RF
TRANSFORMER" will suit your purposes, more than adequately.

The winding to the 50 ohm source will be half the turns of the 100 ohm
winding--and there is no electrical connection between windings--i.e.,
the 50 and 100 windings are separate on the core.

- - - - - -

Usually the turns ratio of an impedance-matching transformer is the square
of the impedance ratio. If the turns ratio, primary to secondary, is N
the secondary voltage Vo is N times the primary voltage Vi but the
secondary current Io is the primary current Ii divided by N. If the
primary is fed from a source of impedance Zi, and Zi = Vi/Ii, then on the
secondary side we have Zo = Vo/Io = NVi/(Ii/N) = (NxN)Vi/Ii. So Zo =
(N^2)Zi or N = square root of (Zo/Zi).

An impedance ratio of 2 would require a turns ratio 1.4. I wonder if
there's a reason why this case would be different.

Chris


Ooops, I missed out the important word 'root' in my first line above!

The impedance ratio is the square of the turns ratio.
The turns ratio is the square-root of the impedance ratio.

Chris