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

On Jan 16, 6:52*pm, 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

It's harder to build a 2:1 balun.. a 4:1 is a 2:1 turns ratio, and
more common (yes, one can do 3:2, that's 1.5:1 turns, 2:25:1 Z)

7:5 turns ratio is 2:1 balun;
3:2 turns, as suggested, is 2.25:1: SWR 1.1:1 is good...

Gianluca

"Tad Danley" wrote in message
...
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

the simpler match is 1/4 wave of 75 ohm cable.

the simpler match is 1/4 wave of 75 ohm cable.

For a narrow band...

Gianluca

"Tad Danley" wrote in message
...
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

--------

I am beginning to suspect that traditionally made baluns are not as exact in
practice as they are theoretically. This is not a surprise, really. Few
things in electronics are exact as we humans like to assume, as you well
know.

Good seeing your post, OM.


Ed Cregger, N2ECW former NM2K

"Ed Cregger" wrote in message
...

"Tad Danley" wrote in message
...
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

--------

I am beginning to suspect that traditionally made baluns are not as exact
in practice as they are theoretically. This is not a surprise, really. Few
things in electronics are exact as we humans like to assume, as you well
know.


the baluns are exact, the practical antennas aren't.

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?

The resonant feedpoint of the 80m loop that I modeled
with EZNEC is 115 ohms. Without a 4:1 at the feedpoint,
the 50 ohm SWR is 2.3:1 inviting foldback. With a 4:1
balun, the 50 ohm SWR is 1.7:1 with no foldback. It is
rare for the feedpoint resistance of a loop to be exactly
100 ohms.

Of course, if the loop is fed with high-Z0 ladder-line,
the 100 ohm feedpoint resistance is transformed to a higher
impedance value where a 4:1 balun might be more effective.

For single-band operation, most hams simply feed the loop
with 1/4WL of Z0=75 ohm coax (quarter-wave transformer).
--
73, Cecil http://www.w5dxp.com

"Dave" wrote in message
...

"Ed Cregger" wrote in message
...

"Tad Danley" wrote in message
...
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

--------

I am beginning to suspect that traditionally made baluns are not as exact
in practice as they are theoretically. This is not a surprise, really.
Few things in electronics are exact as we humans like to assume, as you
well know.


the baluns are exact, the practical antennas aren't.

Only in theory. Such things as variances in construction materials from one
batch to another and the variations that one human will introduce to
construction versus another human also induce characteristics that do not
always jibe with theory.

I admit that I am argueing a very fine point here, Dave, but folks without
any electronics education, but who have pursued electronics theory as part
of their amateur radio advocation, are sometimes prone to thinking that
everything is exact. In the real physical world, few things are exact. Ask
any technician or machinist.

Ed, N2ECW

On Sat, 17 Jan 2009 12:48:05 -0500, "Ed Cregger"
wrote:

I am beginning to suspect that traditionally made baluns are not as exact
in practice as they are theoretically.

the baluns are exact, the practical antennas aren't.

Only in theory. Such things as variances in construction materials from one
batch to another and the variations that one human will introduce to
construction versus another human also induce characteristics that do not
always jibe with theory.

I admit that I am argueing a very fine point here, Dave, but folks without
any electronics education, but who have pursued electronics theory as part
of their amateur radio advocation, are sometimes prone to thinking that
everything is exact. In the real physical world, few things are exact. Ask
any technician or machinist.

Any technician or machinist has only a remote association with exact
anyway. I've calibrated their tools and know how inexact they are.

However, returning to the context of BalUns, a person can choose to
fail, or simply fumble along when it comes to their design,
construction, or application - but this is not a performance fault of
the class of BalUn. Using your 160M BalUn for 1.2GHz work isn't a
blight on the BalUn, but on the user's inappropriate application
(hammering in a screw for example).

The test data I've seen for careful constructions have remarkable
attributes that defy typical construction projects pursuing other
goals. Jerry Sevick's work reveals less than 0.02dB variation of
insertion loss over the HF range for one of his constructions. The
value of insertion loss it does present is less than 0.1dB. The
ability to duplicate his work is not outside the capability of any
individual who writes to this group - but anyone could certainly slop
it into oblivion if care was not high in their mind.

The specs I offered above came of simply opening the book and
describing the first page that offered test results. Scanning further
for better examples yields better examples. As a class, BalUns are
rather exceptional performers.

So, to this casual off-hand remark of BalUns not being as "exact" in
practice as in theory begs the question: "How exact?" When I see
such manufactured controversies conjoined (through other authors) with
turns-ratio, the discussion of BalUn operation is showing stress
fractures in understanding - not theory.

73's
Richard Clark, KB7QHC