I've been enjoying several Lazy H antenna I built for 10 meters that
are being fed with 450 ohm ladder line back to the tuner. They
antennas are performing well. The problem is the external baluns I am
using back at the tuner heat up even at 100 watts. These are suppose
to be 1.5 kw baluns, but they can't handle the impedance mismatch for
full legal limit. I have commercial 1:1 voltage baluns and 4:1
voltage baluns.
I decided to build an air core balun in hopes of saving myself the
expense of buying several torrid cores. The problem is none of the
plans listed in the Bill Orr handbook or that I have found on the
Internet actually work. On my one commercial 4:1 balun if I place a
200 ohms resistor across the leads of the balun I get an SWR reading
of about 1.1:1. When I build the air core balun listed in the William
Orr handbook I get a 2.5:1 SWR.
Hmm..So I decided to try some 4:1 air core balun designs off of the
Internet as well. I found the web page below;

"A 4:1 Air-wound Balun"
http://combotec.com/projects/balun14/balun14.html

I built the balun exactly like the web page described. It does not
work. 2.5+ SWR on 10 meters with a 200 ohm resistor plugged up to the
terminals. The same 200 ohm resistor shows close to a 1.1 on a
ferrite 4:1 balun.

So, the Bill Orr 4:1 air core balun listed in his handbook does not
work on 10 meters. Neither does his 1:1 air core balun when tested on
10 meters with a 50 ohm resistor. The 4:1 air core balun listed on the
web page above does not work either. I'm getting tired of building
air core baluns that don't work.

So....,does anyone have any plans for a 4:1 air core balun for feeding
450 ladder from a tuner that you have actually tested and used that
and it shows close to a 1.1:a SWR when presented with a 200 ohm load?

By the way, of the 4 or 5 1:1 commercial baluns I purchased back in
the 1990s only one of them actually shows a 1.1:SWR when presented
with a 50 ohm load. The others show between a 1.7:1 and 2.1:1 SWR on
10 meters, and that is among several baluns that were all the same
model from the same manufacturer. I'd post the brand name, but the
paper brand labels wore off years ago. I can tell you it has little
brass machined screws and brass holders on the sides of the balun and
not the piece of copper wire coming out to the eye hooks. They are
enclosed inside the typical white PVC pipe with caps on each end and a
coax connector at the bottom.

Michael Rawls
KS4HY

On Jul 2, 6:10*pm, Michael wrote:
I almost forgot ..They need to be air core baluns that can easily
handle legal limit.

Thank you.

Michael Rawls
KS4HY

Michael wrote in news:e820bd25-b016-45f3-9511-
:


I've been enjoying several Lazy H antenna I built for 10 meters that
are being fed with 450 ohm ladder line back to the tuner. They
antennas are performing well. The problem is the external baluns I am
using back at the tuner heat up even at 100 watts. These are suppose
to be 1.5 kw baluns, but they can't handle the impedance mismatch for
full legal limit. I have commercial 1:1 voltage baluns and 4:1
voltage baluns.

Therein lies a possible explanation of your problems.

If you view the 4:1 voltage balun as device that can transform any load
from say 5+j0 to 5000+j0 (just staying on the X=0 axis) at 1kW (for
round numbers), you expected it to handle 15A, and withstand 3000Vpk,
over more than a decade freqency range, and to have a maximum loss of
say 20W (which is about enough to heat the core in most enclosures to
Curie point) or 98% efficient.... and then give a near ideal impedance
transformation.

Well, it just doesn't happen that easily... as you now know.

Owen

Michael wrote in
:
....
So how do I go about feeding a Lazy H with ladder line back to the
tuner for high power without over heating the balun? The tuner is a
Dentron MT-3000a. The built in balun is not balanced at all at 10

I will respond in a couple of hours, but in the meantime, please clarify
that everything between the ATU and LazyH is up for consideration.

What impedance line are you using?

Do you feed the antenna midway between the elements of at one element
(branch or distributed feed)? What do you think the feed point impedance
is?

What band(s)?

Owen

On Jul 2, 7:05*pm, Owen Duffy wrote:
Michael wrote :
...

* So how do I go about feeding a Lazy H with ladder line back to the
tuner for high power without over heating the balun? *The tuner is a
Dentron MT-3000a. *The built in balun is not balanced at all at 10

I will respond in a couple of hours, but in the meantime, please clarify
that everything between the ATU and LazyH is up for consideration.

What impedance line are you using?

Do you feed the antenna midway between the elements of at one element
(branch or distributed feed)? What do you think the feed point impedance
is?

What band(s)?

Owen

I am using 450 ladder line. The Lazy H is center fed with 1/2 wave
spacing between the top and bottom elements and the elements are 1/2
wave elements. 450 ladder line is connecting the top and bottom
elements. I am not using the expanded Lazy H version. This is the
classic center fed Lazy H design as shown in the ARRL antenna
handbook. I only intend to use the antenna on 10 meters. I don't
know what the exact impedance is (sorry). The Lazy antenna is about
50 feet off the ground at the top wire. The amplifier I want to use
with the Lazy H is a Drake L4B with two Eimac 3-500z tubes.

Michael Rawls
KS4HY

Michael wrote in
:

On Jul 2, 7:05*pm, Owen Duffy wrote:
Michael wrote
innews:7c2889df-092d-4471-bfb2-6db
:
...

* So how do I go about feeding a Lazy H with ladder line back to
the tuner for high power without over heating the balun? *The tuner
is a Dentron MT-3000a. *The built in balun is not balanced at all
at 10

I will respond in a couple of hours, but in the meantime, please
clarify that everything between the ATU and LazyH is up for
consideration.

What impedance line are you using?

Do you feed the antenna midway between the elements of at one element
(branch or distributed feed)? What do you think the feed point
impedance is?

What band(s)?

Owen

I am using 450 ladder line. The Lazy H is center fed with 1/2 wave
spacing between the top and bottom elements and the elements are 1/2
wave elements. 450 ladder line is connecting the top and bottom
elements. I am not using the expanded Lazy H version. This is the
classic center fed Lazy H design as shown in the ARRL antenna
handbook. I only intend to use the antenna on 10 meters. I don't
know what the exact impedance is (sorry). The Lazy antenna is about
50 feet off the ground at the top wire. The amplifier I want to use
with the Lazy H is a Drake L4B with two Eimac 3-500z tubes.

Ok, if we define the feed point to be half way between the dipoles, you
ought expect that the feed point impedance is relatively low, some where
of the order of 50 ohms, give or take some reactance and it is a fairly
balanced / symmetric load. Note that the feed system to each dipole is a
tuned length of transmission line, that makes this a narrowband feed
system.

So, your challenge is to deliver the transmitter a nominal 50+j0 load.

Re the ATU's integral ATU, always regard them as likely to be
unsuitable.

Let's regard that, integral balun aside, your ATU is probably capable of
matching a fairly wide range of impedances at 10m with reasonable
efficiency.

If you objective in using a balun is to minimise feedline direct
contribution to radiation, your objective is to try to force equal but
opposite currents in each conductor.

An ideal voltage balun will approach that objective ONLY with a
perfectly symmetric load. If you think you have a perfectly symmetric
load, it is probably because you haven't measured it.

An ideal current balun will approach the curent balance objective
irrespective of load symmetry, so it is a better choice for your
application.

Why do you need a 4:1 transformation? Depending on your feedline length,
the impedance presented to the ATU may be as low as somewhere round 50
ohms, and perhaps as high as several thousand ohms. It might seems good
to transform several thousand ohms by a factor of 4... but transforming
the lower impedances by a factor of 4 exacerbates ATU losses.

Since wavelength is short, I would be inclined to try to use a feedline
length of an integral number of half waves, and an effective 1:1 current
balun at the ATU. This minimises working voltages within the balun and
ATU (reducing risk of flashovers), without driving high losses in the
ATU are very low impedances.

If you think about your own requirements, and finding a solution that
fits, you will do better than Googling up HamUniverse articles and the
like.

Owen

On Jul 2, 8:39*pm, Owen Duffy wrote:
Michael wrote :

Since wavelength is short, I would be inclined to try to use a feedline
length of an integral number of half waves, and an effective 1:1 current
balun at the ATU. This minimises working voltages within the balun and
ATU (reducing risk of flashovers), without driving high losses in the
ATU are very low impedances.

If you think about your own requirements, and finding a solution that
fits, you will do better than Googling up HamUniverse articles and the
like.

Owen

When I calculate the feedline length am I correct in assuming that I
need to take in to account the velocity factor of the 460 ohm ladder
line?

Michael Rawls
KS4HY

Michael wrote in
:

....

When I calculate the feedline length am I correct in assuming that I
need to take in to account the velocity factor of the 460 ohm ladder
line?

Yes Michael, it is the electrical length that is important.

You can use TLLC http://www.vk1od.net/calc/tl/tllc.php to calculate the
approximate length of Wireman's ladder line to give you some idea. If
you specify the length in wavelengths, the results will show you the
physical length in metres. Divide that by 0.3048 to get feet.

The length is not terribly critical, you are just trying to feed the
thing near a current maximum rather than a voltage maximum.

If your balun requirement becomes an effective current balun that need
only suite 10m, then a number of options spring up, but a ferrite cored
balun similar to a general purpose HF balun, but with slightly less
turns is likely to give superior performance for the high end of HF.

If you want to read more on the reasoning behind my recommnedations, I
can give you some links.

Owen

On 2 Jul,
Michael wrote:

So....,does anyone have any plans for a 4:1 air core balun for feeding
450 ladder from a tuner that you have actually tested and used that
and it shows close to a 1.1:a SWR when presented with a 200 ohm load?

Why not just use a(n electrical) half wave loop of coax if you are only using
it on 10metres? Or even just a Pawsey stub for a balun and match elsewhere.
You can do a lot of (single band) matching with just a quarter wave of open
wire line with shorts/open circuits and taps.

--
BD
Change lycos to yahoo to reply

Hey OM
The baluns I like to use are choke baluns and real transmission line
baluns, for ten meters and a 66% velocity factor coax that is 11ft of
RG213. That is 4:1 on ten meters only. And the high current, high
voltage nodes are at the ends of the coax.
73 OT
de N8ZU




On Jul 3, 6:50*pm, wrote:
On 2 Jul, *
* * *Michael wrote:

So....,does anyone have any plans for a 4:1 air core balun for feeding
450 ladder from a tuner that you have actually tested and used that
and it shows close to a 1.1:a SWR when presented with a 200 ohm load?

Why not just use a(n electrical) half wave loop of coax if you are only using
it on 10metres? Or even just a Pawsey stub for a balun and match elsewhere.
You can do a lot of (single band) matching with just a quarter wave of open
wire line with shorts/open circuits and taps.

--
* BD
* Change lycos to yahoo to reply