As several on the reflector have asked, here it is. And thanks for asking.
The monster balun, often referenced as "the ugly balun" is made of some 18
to 20 ft of RG-213 coax, close wound on a piece of 3" OD PVC. The RG-213
coax is preferred because of the solid dielectric. (A foam dielectric cable
being put in a tight wound condition will allow the center conductor to
migrate inward and eventually short to the shield.) The idea is to have as
many turns possible as opposed to larger diameter turns. These should be
flat wound carefully side-by-side. Getting much smaller than 3" makes
winding and working with the project more challenging. Feed one end as
though it is 50 ohms unbalanced and the other end as a balanced feed.
For construction, I typically drill a couple of holes about 1" apart in one
end of the PVC to use as terminals for the balanced feed point, fitting them
with some brass bolts, washers and nuts. I use wire lugs on the shield and
center conductor of the coax, both crimping and soldering them in place and
placing them under the nuts of the screws. This will hold one end of the
coax securely. If you intend to use the balun outside then be sure to use
some duct seal or some other water proofing method to assure that water will
not get into the open end of the coax. Then wind the remainder of the coax
on the PVC form. At the end, drill a couple of holes through which I pass a
zip tie or wire tie to secure the other end, leaving a pigtail of 6" to 12".
To that end I install a PL259. Now you have the "ugly balun".
I've measured the balance with this configuration at multiple frequencies
between 1.8 MHz and 30 MHz to find quite a good balance regardless of the
load Z or reactance posed to the balanced end. As to power handling, the
rating of the coax is it. For RG-213 this is higher than most hams can
generate in watts. I usually mount the balun at the base of the tower being
sure to keep it away from the tower by the length of the coil or more.
Usually about 18". The coax goes to the tuner in the house.
In all frankness, I prefer to bring the balanced feed line direct into the
operating position where it is attached to the "ugly balun". The pigtail is
then attached to the tuner which is a Tentec 238 L network.
If you have any questions or need additional information on balanced feeds,
various tuners and such, ASK. I prefer to NOT take up space and time here
on the reflector with the topic but be assured I will answer each and every
e-mail to the best of my abilities.
73
Bob, K4TAX
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