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The 2 Meter Collinear J Pole Antenna Project
Get ready for field day, mountain topping, emergency
communications, roaming or just plane ham radio fun with this portable
inexpensive 2 meter J designed to fit into a small foldup space that
yields about 8db gain.
some of the club members may have noticed I enjoy making my own antennas
and sometimes from the most unusual materials, however a quick flick
through my log book tells me I must have gotten something right......(well
"This project came about as I was looking for a high gain
omni directional antenna to use in the field. I needed something that was
light weight and could be carried in a small package when
"Oh yes, I made the most of my 10 watts and didn't
rob the bank.
After some unsuccessful experimenting using capacitors
for phasing the elements, I settled on a stacked j pole consisting of four
half wave radiating elements, with each element taken 180 degrees out of
phase using a half wave phasing section that separates each radiator. If
all that sounds like nonsense don't worry."
"I have simplified it by
giving all the numbers (see diagram
at the end of the article) and the materials
that I have used, but use your imagination if you cannot use or source the
same materials. "
started to build the antenna by cutting four lengths of wire, the
measurement is 38.75ins for a half wave @ 145mhz but I cut them at
39.75ins to compensate for the joints. The wire I used was multi stranded
insulated wire that was from a discarded lawn mower lead.
The end of
each length I stripped back 1/2 inches of insulation, the next step I
cut 3 lengths of twin and earth and here I used the insulated wire (red
and black wires) the length of each wire is 38.75ins again half wave
lengths, these are for the phasing sections that separates each element. I
folded each in half and mounted them on plastic lids which are used for
fast food containers, (scrounged from work), using cable ties to keep them
secure .I soldered the four elements to the three phasing sections. The
gap of the phasing elements is 3 inches…see photos and diagram
"After construction, support it from a non-conducting
collapsable fishing pole or simular support for final swr testing using
plastic or nylon wire or cable ties, string or other non-conductive
temporary material. Atttach center conductor of coax to longest element,
shield to shortest. Move the coaxial cable connections up and down for
lowest swr and solder or use alligator clips for the connections. (You may
want to just use alligator clips at ends of coax connections for easy swr
adjustment for changing conditions in the field.) "
"After you have
completed the antenna, you can have some fun with it or just fold it up
for your next adventure in the great outdoors! Make sure your support in
the field is non-conductive. This antenna could possibly be attached to a
rope and hung from a tree
The 19 1/4 inch matching
transformer section (picture above) at the bottom of the antenna
was made from two lengths of alloy tubing spaced 1.8 inches apart and
screwed to two plastic insulators to keep them
Antenna "Test" range!
UGLY BALUN (CHOKE)
Use 8 turns of 50 ohm coax close wound and attached to
suitable length of PVC as close as possible to antenna with one end
connected to antenna and other end to
The 19 1/4
inch matching transformer section at the bottom of the antenna was made
from two lengths of alloy tubing spaced 1.8 inches apart and screwed to
two plastic insulators to keep them parallel.
FORMULA FOR CALCULATION OF
Top Section and other
2808/freqmhz = inches
8424 / 146 = 57.69 inches
/ 146 = 38.45 inches
2808 / 146 = 19.23 inches
LONGEST BOTTOM SECTION LENGTH INCLUDES ONE SIDE OF THE 1/4 WAVE MATCHING
None of these measurements are extremely critical and
a good antenna analyzer could be helpful but use what you have and have
fun with Sean's project.
Use the formulas for other bands
Thanks to Sean, M3FVB
Email him for questions here
original article here. You will leave this
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