Building Coils for a
Portable Dipole Using A Novel Method of Winding Coils with
Weedeater cord! A COIL WINDING
TECHNIQUE THAT LENDS ITSELF TO A PORTABLE DIOPLE
CONFIGURATION By
K4MMG
WHY? It all
started when I priced a 10 inch air inductor! Here is my way of
saving money!
OBJECTIVE:
Build a coil that will use
the materials that I have on hand, saving money, will be fairly
rugged, and allow use from 17 through 10 meters. Most importantly,
the coil wire needs to be bare so that a clip lead method can be
used to adjust taps as the frequency is changed, and the coil wire
turns can not short to each other.
While the coil described
is used in a dipole configuration, it can be adapted for other
applications as well. Remember this article is slanted more towards
how to build a coil than how to build an antenna, and to save on the
cost of an air wound inductor that in addition to price , does not
lend itself to be rugged enough for portable use.
CONSTRUCTION:
Using a 12 inch
,1-1/2" diameter plastic section of a sink drain pipe, cut it in
half. So that the wire turns will not slip too easily, add a strip
of duck tape on one side, then the other. On one side , and in
line with each other, drill two holes that will clear a
6/32 bolt ½ inch from both ends. Repeat this for the opposite
side as well. You should have 4 holes
all together. So that you can connect to the coil windings with
a clip, there will need to be a slot cut on one side of the coil ,
between the two holes about 3/8 inches in from each hole (see
drawing below).
Mark the slot to be cut out , secure the drain tube so
that it won’t move when you are making the slot. Use a Dremel type
tool , or a solder iron with a cutting blade to cut the slot. What ever method that you use please observe all
safety precautions. With two of the holes on the same
side, and on the same
side as the slot, insert a 6/32 bolt and nut,
(configure so that the threads are protruding from the side that the
wire is to be wound). Have two washers and another nut
available.
At this point you need to
decide if you want to wind a coil so that taps can be used or not.
If not, then wind the turns as tight
as you can get them. If you will be using
taps, wind the turns firmly so that they can slide a
little.
The wire that I
used is # 18 Alcotec Part # ER 5356, 1/16
dia. welding wire. In the photo below, it is the silver color.......
not the orange! YOU CAN ONLY BEND THIS WIRE ONCE IN A HOOK
CONFIGURATION. Now
bend the hook on one end of the wire, place it over the 6/32 bolt,
using a washer then the wire , washer and finally the nut,
tighten. Continue winding the turns until you get 28
turns as evenly spaced as you can. When you reach the other 6/32
bolt, make a hook and tighten the wire between the washers. Look at
your coil, if you are satisfied, and no turns are shorted proceed to
the next winding sequence. When you reach the other 6/32
bolt, make a hook and tighten the wire between the washers. Look at
your coil, if you are satisfied, and no turns are shorted proceed to
the next winding sequence that is the "secret" to the success of
this coil!
Locate a roll of "weed eater" .095 line.
(Orange in photo below) In the hole on the opposite side of one
of the 6/32 bolts insert one end of the line, wind it so that it
goes between the wire coil already wound. Pull each turn as tight as
you can, when you reach the end, thread the line through the
remaining hole. Leave a few inches protruding from each end. The
weed eater cord is used as the insulator between the wire coils. You
now have a non shorting fairly rugged coil for portable banging
around with.
Prototype example of coil details
showing welding wire with weed eater cord between
coils.
Completed 28 turn
coil
MY APPLICATION:
The reason that I selected this
particular size coil form was that it fits nicely over the ¾ end cap
that supports the 4 foot telescoping antenna used on my dipole, as
pictured above. My use was for 17 through 10 meters mainly
because of the height above ground required. For me, portable
operations for 17 meters was doable. The antenna pictured has
supported 100 watts SSB. I’ll only use the FT-817 in conjunction
with it for portable use however. This 28 turn coil allows operation
from 11-30 Mhz. If you decide to build a dipole, make sure that
some type of isolation transformer is used at the antenna feed
point.
CONCLUSION: Use all
kno{1}wn safety precautions. This is an amateur experiment and
should be treated as just that. As with all experimental projects,
your results may vary depending on your particular situation.
The welding wire that is noted has been in use on my HF quad for
8 years looking as new as the day it was placed into operation.
I think this method of winding these coils
is more functional and proves that "Necessity is the Mother of
Invention"!
ACKNOWLEDGEMENT:
As you can determine from one of the
photos, the configuration is similar to that of the widely popular,
"Buddipole"
by W3FF. How to build your own Buddipole
is described in detail on the
W3FF web site, along with the for sale commercial version details.
Make sure you check out the commercial version! It's a winner with
reviews to prove it!
My configuration is a variation of this
do it your self information, excluding the previously described coil
of course.
MATERIALS: for the coil
only
12" plastic sink drain pipe, 1.5"
diameter
roll of # 18 Alcotec Part # ER 5356,
1/16 dia.welding wire
roll of weed eater line .095 diameter
(chose your own color)
