steveeh131047 wrote:
But one question would be how to build this ideal 1:9 transformer
which maintains its transformation ratio and exhibits zero loss across
the wide range of impedances and frequencies involved.

Has there been any information published on loss and
transformation measurements for real world TLTs used
far outside of their design impedances?
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Owen,

If I've managed to read my lab notes correctly, these were the
differences in loss (ground+feedline+tuner) - with and without an
ideal 9:1 transformer at the feedpoint - for a 33ft vertical over
average ground fed with 50ft of RG213. I assumed ground losses of 20
ohms. Positive figures indicate that the losses were lower with the
transformer:

160m -1.6dB
80m +6.02dB
40m -2.3dB
30m +2.1dB
20m +4.4dB
17m +3.86dB
15m -0.55dB
12m +1.6dB
10m +2.9dB

Of course this data was for one specific scenario, but I guess you'd
look at it and say that for this case, on balance, the inclusion of
the transformer was of benefit. But now factor in some realistic
transformer losses and it might not look so clear cut.

73,
Steve G3TXQ

On Oct 5, 2:10*am, Cecil Moore wrote:

Has there been any information published on loss and
transformation measurements for real world TLTs used
far outside of their design impedances?
--
73, Cecil, IEEE, OOTC, *http://www.w5dxp.com

Cecil,

Martin has some data under the heading "33ft Verticals and 4:1 Ununs "
he
http://g8jnj.webs.com/currentprojects.htm

73,
Steve G3TXQ

steveeh131047 wrote in news:46a67bfc-c375-4533-8df0-
:

On Oct 5, 2:10*am, Cecil Moore wrote:

Has there been any information published on loss and
transformation measurements for real world TLTs used
far outside of their design impedances?
--
73, Cecil, IEEE, OOTC, *http://www.w5dxp.com

Cecil,

Martin has some data under the heading "33ft Verticals and 4:1 Ununs "
he
http://g8jnj.webs.com/currentprojects.htm

Steve,

Here are the input impedance and VSWR(50),Loss graphs for my model of a
FT240 #61 with 12 bifilar turns with a 1000+j0 load.

http://www.vk1od.net/lost/Clip045.png

http://www.vk1od.net/lost/Clip046.png

Non-ideal transformation ratio is not a big issue for an unun used with
an ATU, voltage withstand and loss are higher priority.

The balun loss data in the article at http://vk1od.net/blog/?p=568 was
obtained by measuring the balun using a VNA, and creating a spreadsheet
that solved the balun + load network for an arbitrary load impedance. The
spreadsheet is revealing, as one can immediately see the broadband
peformance of the balun with extreme loads, R and X in arbitrary
combination.

What I do know is that it is superficial to describe a balun (or unun)
with just two metrics such as 5kW, VSWR1.5... but have a look at
commercial baluns, that is how they are often (mostly) sold. There is the
odd manufacturer that gives a loss and VSWR curve on a nominal load FWIW,
but I have not yet seen any manufacturer publish a set of S parameters
covering the operating range.

I am not naive about magnetics, they are challenging devices, but at
least in the ham radio market, it is more black magic than good sense.

BTW, if you look at the loss graph for this device with a 1000+j0 load,
and assume that it can safely dissipate perhaps 20W continuous, it is
capable of less than 1kW continuous at 30MHz, but some manufacturers
build such a transformer and rate them at 5kW or more. With a load
impedance of 4k+j0 (eg a full wave dipole), the loss is even worse, and
the continous power rating even lower.

Owen

Thanks for the numerous comments on the unun / balun, but I read nothing on the
possible convenience to use a 300 ohm flat ribbon in place of coaxial. No
interest for that issue?

73

Tony I0JX

On Mon, 5 Oct 2009 17:39:28 +0200, "Antonio Vernucci"
wrote:

but I read nothing on the
possible convenience to use a 300 ohm flat ribbon in place of coaxial.

On Sat, 03 Oct 2009 13:39:12 -0700, Richard Clark
wrote:

If your BalUn has already done the bigger job of turning a High Z to a
modest one, the common logic for the need for twin line has also been
diminished.

73's
Richard Clark, KB7QHC

If your BalUn has already done the bigger job of turning a High Z to a
modest one, the common logic for the need for twin line has also been
diminished.

Yes but my question regarded the advantage of twin-lead vs. coaxial in that
particular application where impedance is uncontrolled.

73

Tony I0JX

On Mon, 5 Oct 2009 21:17:26 +0200, "Antonio Vernucci"
wrote:

Yes but my question regarded the advantage of twin-lead vs. coaxial in that
particular application where impedance is uncontrolled.

http://www.vk1od.net/calc/tl/twllc.htm

73's
Richard Clark, KB7QHC

"Antonio Vernucci" wrote in
:

If your BalUn has already done the bigger job of turning a High Z to
a modest one, the common logic for the need for twin line has also
been diminished.

Yes but my question regarded the advantage of twin-lead vs. coaxial in
that particular application where impedance is uncontrolled.

Tony, it depends on the details of your scenario, and may be different at
different frequencies.

Unless you believe in the myth that ladder line is *so* low in loss that
you *never* need to consider it, you need to calculate it out to really
know... it is not a no-brainer as we say, in fact it is a quite complex
problem to solve (mainly quantifying the loss and transformation in
transformers which both Roy and I have mentioned in this thread).

BTW, from time to time I see articles that recommend twin line for direct
feeding a ground mounted vertical (ie without using a balun at the feed
point). It is as insane as using a 4:1 voltage balun with coax at the
base of such a vertical, because both types of feed drive substantial
common mode current on the feed line. A review of such an article is at
http://vk1od.net/antenna/multibandun...tical/BSUM.htm , this one
using a magic ingredient, Belden 8222 twin feedline which Belden ceased
manufacturing. But... I am sure some hams have got the QSLs to prove that
it "works real good".

Owen