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.
"As 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 sometimes!)."
"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 collapsed…"
"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. "
Construction
"I 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 ฝ in 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 below."
"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 limb."
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 parallel.
The Antenna "Test" range!
UGLY BALUN (CHOKE) AND CONSTRUCTION
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 radio.
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 SECTION LENGTHS
Longest bottom Section 8424/freqmhz = inches
Top Section and other sections 5616/freqmhz = inches
Matching Section 2808/freqmhz = inches
EXAMPLE:
146mhz Center frequency
Longest section 8424 / 146 = 57.69 inches
Top section and others 5616 / 146 = 38.45 inches
Matching 2808 / 146 = 19.23 inches
Note: The LONGEST BOTTOM SECTION LENGTH INCLUDES ONE SIDE OF THE 1/4 WAVE MATCHING SECTION.
