Step By Step - How To Make A Monster 4:1 Balun
The steps taken here are based on the balun in the ARRL Handbook
but have been modified.
The ARRL Handbook shows an example of making a 4:1 balun
flat wound, with one core. My version uses 12 T200-2 vertically wound cores,
it also uses 12 ga. Teflon wire instead of 14 ga. enameled wire.
Throughout this document many of the steps are based on what I had
available but do not necessarily mean they are the only route.
When a step is based on availability it will be noted.
The maximum output rating of this balun is unknown,
but theoretically it should be much, much more than any legal
limit transmitter can throw at it. (With any resonable antenna.)
What You'll Need
The Enclosure
The enclosure should be metal but does not necessarily have to be
the one I have chosen. Why metal and not
plastic? Many balun
designs show baluns built in plastic enclosures. Many on the market
also come in plastic
of some sort. I prefer metal for a good solid
ground and shielding. For this particular balun you want at least
a
7"(L) x 4.5"(W) x 3"(H) enclosure. I chose to use a
7"(L) x 5"(W) 3"(H) simply because it was what I
had
on hand.
Setting Up The Enclosure
I drilled 15 holes in my enclosure.
Make sure your locking nuts (The first nut you threaded on) are
good and tight You want your
lock washers to make a good bite into
the metal..
Winding Your Transformer
I used black electrical tape to hold my cores together while I
wound them. This is much easier than
trying to wrap loose cores.
This tape can be removed in the final product but for now you'll find
it a
necessary step. You want a 2 x 6 configuration.
If you
used a straight 24 foot piece of wire now would be the time to fold
your wire in half and cut it
into two equal pieces. Stretch out
your wire for the primary and secondary, feed the two wires
through
each side of the cores. Center your wires so you have equal lengths
on both ends. Now
begin wrapping. You want 10 wraps total with all
4 ends facing up.
Mounting The Board
This is a method purely by choice, I used 1/2 ceramic standoffs
because that's what I had on hand.
They are also convenient for
the zip ties I used to secure my transformer. (More on that later)
But
you can use whatever you have on hand to attach the board to
the enclosure. Epoxy works great, so
would weatherproof double
sided sticky foam. I used a large perfboard because it's what
I had.
There certainly is no need to use the same size. Use what ya' got!
Place your board in your enclosure and center it so that there is
room for the balun and the
windings. Make note of its position
and drill your holes. (or however you chose to mount the
board.)
Finalizing The Transformer
Set the transformer in it's place and make note of the lengths of
wire needed to reach the proper
terminals.
First, trim, twist, tin, and solder your grounds each to it's own
eyelet. This will be 2 ends
of one primary and one secondary one from each side of the transformer. 
Take the 2 remaining ends and trim them to fit to the 2 balanced
line outputs. Twist, and tin your
ends, and solder your eyelets to
each end. Bolt one end on each stud of your ceramic feed throughs
.
Next take a bit of your wire and place it between one of your
ceramic feed through studs (I chose
the rear stud) and the SO-239,
trim and tin both ends, solder an eyelet on one end and bolt it to
one
stud on your feed through. Then solder the other end to your
SO-239. Double check all your
soldering!
Attaching The Transformer
Place the transformer in it's resting place without attaching it.
This is when you can remove the tape
you used to hold the cores
together. The wires should hold the transformer together at this
point. In
fact if you use epoxy I highly recommend it. The tape
may prevent the epoxy from biting in. I used
zip ties because
that's what I had. You can also use double sided sticky foam here too
if you wish.
Mounting Your Balun
Unless you've taken some precaution to weather by sealing your
enclosure with silicone for example.
I highly recommend that you
put it somewhere outside of your shack, but out of direct exposure
to
weather. I don't recommend potting because if you need to
service your balun you're screwed.
You'll need to drill more
holes in the back of your enclosure to mount it to its final resting
place.
(This is why I chose an enclosure with some slop room in
it,) Once done, solder on your eyelet on
a piece of your wire, and
connect your earth ground to the bolt with the wing nut to a
grounding rod.
** Note a GOOD earth ground is mandatory, you
don't want your balun to seek ground all the way
through your coax
to your shack! This can cause all sorts of nasty problems! Which is
why I also
suggest a metal enclosure.
Connect your coax
cable coming from your shack to the SO-239 and the balanced line from
your
antenna to the feed throughs.
You're Done!
Bolt your enclosure together and enjoy! See you on the air!
de Randy,
N3LRX (YellRX)
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