Print

Can anyone send me information on how to build a 9:1 Balun? My email address is normally@softcom.net  Thank you Bill  AC6IJ

[DL7IO]

try this link:
http://www.hayes06.freeserve.co.uk/phbalun1.pdf
best regards
Holger, DL7IO

Thanks for the information on the Paul Hayes Quadrifilar Helix Antenna Trifilar Balun Construction for QHA.  No reference was made though in the artical as to what the balun is or what exactly is it used for? If it is indeed a 9:1 balun, it is just what I'm looking for.  Thanks again DL7IO for the information. What a great job of explaining how to build the balun.   Bill AC6IJ

[WB6BYU]

I looked up the reference link, and this appears to be a 1 : 1 balun.
(Looking at the wiring diagram, the coax is connected across two
windings and the load is connected across two windings, so there
is no impedance step-up.)

For a 9 : 1 balun, the necessary turns ratio is 3 : 1.  You could
convert the 1 : 1 to a 9 : 1 by connecting the coax across only
one winding and the load across all three windings.  However, the
coax braid would no longer be connected to the center tap on the
load side, because, with 3 windings in series, there is no tap at the
center.  If you want to do this all with one set of windings, you need
6 windings in series, with the coax connected across two of them.
(The braid connects to the center, and the center conductor
connects one winding in from either end.)  However, it is difficult
to get close coupling with 6 parallel wires, so it may not work as
well in practice as it does on paper.

Perhaps a better approach is to separate the balun function from
the impedance transformation function.  First, use a 1 : 1 balun to
convert the coax to 50 ohm balanced output.  The balun on the
linked page is one example, or several turns of coax through a
large ferrite core could also work.  Then transform this to 450 ohms
using a 3 : 1 transformer (for example, using the basic trifiliar design
but connecting the load across all 3 windings and the 50 ohm
balanced connecting across just the center winding.)

Before you start building, however, make sure that the design you
are using is suitable for the frequency range you want to cover.
You didn't say what bands you wanted the balun for, and every
design has limits on the bandwidth over which it will work.  The
referenced balun is for a Quadrafiliar Helix, which is most commonly
built at UHF for satellite working.  I didn't see any reference to the
frequency coverage, but, if it is designed for use on 70cm, it won't
work on a 80m Windom.

Perhaps you can share the intended frequencies and applications
for which you want the 9 : 1 balun, and we can help you find
something which will meet your needs.

Good luck ! - Dale WB6BYU

WB6BYU Thanks Dale for your input on this. What I am thinking is that 450 ohm ladderline would be better matched to a 50 ohm coax cable by going through a 9:1 Balun. What difference does the length of the antenna make as long as it is cut for the lowest freq. that I intend to use? My tuner should handle the output from the 9:1 Balun much better than using say a 4:1 Balun.   Bill  AC6IJ

[VE3IAY]

I think you may need to think twice about this. If your ladderline is going to be connected to a 450-ohm load, then you can ignore the rest of this (and please forgive me for telling you what you probably already know). However, if your ladderline is connected to an antenna whose impedance happens to be 50 ohms, the SWR on the 450 ohm line will be 9:1, and the impedance at the other end of the line could vary over a very wide range. If the ladderline happens to be exactly a half-wave long, the impedance presented at the other end will be 50 ohms. Connect a 9:1 balun to this and you will convert the situation from an initially perfect match on the coax to a 9:1 mismatch!

Generally ladder-line is used in an unmatched condition, that is, the load to which it is attached is not at the characteristic impedance of the line. In that case the one thing you can be sure of is that the impedance presented at the end of the ladderline will NOT be equal to the characteristic impedance. Depending on the length of the line, you might need a 1:1 balun, an 81:1 balun, or a more complex matching network.

Another problem is that your 9:1 balun is probably designed to work only for impedances near the design value. If your ladderline is mismatched, the 9:1 balun may see impedances very far from the design value, and it may do a very poor job of rejecting unbalanced currents. You might be better off with a simple 1:1 current balun or coax choke.

For more info on this, you might try looking at http://people.delphi.com/cecilmoore/mystery.htm,
where W6RCA describes how to feed a dipole with an adjustable-length ladderline so as to achieve a good match to coax on all HF bands. Of course, most people just use a tuner.

[DL7IO]

and another link...
http://www.ultrarf.com/assets/applets/appnote3.pdf
with a nice part of impedance matching.
I'm using trifilar wounded 9:1 baluns for beverages. Important is the core and number of windings for the working frequencies. What kind of antenna you want to make?
regards Holger

Thanks again Holger for some interesting articles. So far the antenna that interests me the most is the one at this link: http://users.erols.com/k3mt/windom/windom.htm   It is constructed with a 9:1 balun and quite good detail on how to make one.  I am presently using a G5RV for my all band type antenna and I think it will be very hard to beat. I have plenty of time to try different things so thats what I am doing. 20 meters is probably the band I use the most.. Thanks again Bill  AC6IJ

[WB6BYU]

There are only two times when a 450 ohm feedline will actually
present a 450 ohm to the tuner:
1) when the antenna presents a 450 ohm impedance, or
2) when the feedline loss is very high (over 10dB)
In most amateur installations, the 450 ohm line is not matched to
the antenna, but is used with a high SWR.  This works fine, and it
is an efficient way to get power to the antenna, but the impedance
seen by the tuner is, in most cases, not very close to 450 ohms.

If you are planning to use the balun at the output of a tuner for
matching balanced loads, the 4 : 1 is probably prefered over the
9 : 1 also because most tuners are more efficient when matching
higher impedance loads.  (This is a particular problem with small
commercial "T" tuners which often try to claim 160m coverage using
240pf variable capacitors.  You might be able to tune the SWR to
1 : 1, but still be dissipating half your power inside your tuner.)
For example, say you are using an 80m dipole fed with 450 ohm
line for an all-band antenna.  If the feedline is a half wave on 80m,
then the impedance at the feed end of the feedline might be 50
ohms on 80m and 2000 ohms on 40m.  With a 4 : 1 balun, the tuner
actually would see 12.5 ohms and 500 ohms (we have to make
some assumptions here about the balun behavior, since it wasn't
designed for any of these impedances.)  With a 9 : 1 balun, the
tuner loads would be 5.5 ohms and 220 ohms (making even larger
assumptions about the behavior of the balun at high SWR levels.)
In this case you would be better off using a 1 : 1 balun in 80m and
a higher ratio balun on 40m, an option offered by few, if any,
commercial tuners.  (This example is more extreme than most ham
installations, but  made the math easy to do in my head.  My mental
processor doesn't handle complex impedances well!)

If you are thinking of putting the balun at the feedpoint of a Windom
antenna, I would recommend you review W4RNL's analysis of
"Off Center Fed" dipoles on his web site at www.cebik.com.
If I recall, the impedance is not nearly as constant on different
bands as early estimated had thought.

Good luck! - Dale WB6BYU