K0FF's 6 -meter SLOOP
It is more or less
omni-directional, and horizontally polarized. Copper is the best
possible electrical conductor at normal temperatures, next to
silver. Copper conducts better than gold! Antenna efficiency is
the RADIATION RESISTANCE of the antenna, divided by the
ELECTRICAL RESISTANCE. An antenna made from copper is 1.6 times
more efficient than the same antenna made of aluminum.
It presents a high angle of takeoff when mounted low, and singly (great for Es), can handle 100W. Stack two or more for extra gain if needed.
It's just a dipole folded around on itself, and supported at the far (open) end with a plastic insulator. "Bent Dipole" might be a good term, as a "Folded Dipole" is quite antoher thing.
The Gamma Match:
A low VSWR may be obtained by adjusting the Gamma Match shorting bracket position, and also the length of the tubing and shorting bracket. The Gamma bracket "finds" the 50 Ohm point along the element, and connects that to the Coax connector via the Gamma tube. The additional length of tube adds inductance into the circuit, and this is canceled out by the series capacitance formed between the insulated Gamma wire and the inside of the Gamma tube.
The shape is a closed 28" square, with a mounting /support bar through the middle. This mounting bar is attached to a copper TEE at the drive end, and to a CPVC TEE at the other end. The CPVC TEE acts as support and end-insulator for the radiating element and provides a mounting point for the Butterfly.
A large (3/4") part is used, and adapted down to fit the water pipe, to increase its insulating qualities, as there is very high voltage at this point. A strip of brass or copper 1/2 by 3" is screwed to the outside middle portion of the CPVC Tee, through a small center hole, and is rotated one way or the other as a resonance tuner (Butterfly). When the Butterfly is at right angles to the element, the frequency is the highest, when parallel, it's the lowest.
A Gamma match sets the impedance to 50 Ohms, and the Butterfly adjusts the center frequency. Center frequency is 50.00 to 50.800 with the exact dimensions shown. Typically the 2:1 SWR bandwidth exceeds 500 kHz.
A U bolt and saddle through the central tube provides a center mounting point. Another approach is to install a copper TEE in the center tube, with the open end down. In that open end solder a 1/2" brass rod which has been drilled and tapped for 3/8-24.
Side mounting on a tower can be achieved by using conduit clips to fix it to a horizontal mast.
In some climates where water is a problem, drill small weep holes in the bottom corners. A spray coat of Krylon Clear Enamel will keep the copper shiny. If used mobile, you may use a colored paint, the same shade as your vehicle.
1/2" Copper waterpipe :
3 ea. 27 inch piece
4 ea. 12.5 inch piece
4 ea. Copper 90 Degree elbow
1 ea. Copper TEE
Other Copper or Brass :
1 ea. 13.5 inch piece 3/8 i.d. Copper refrigeration tubing ( Gamma tube) *
1 ea. Brass plate 1/2" x 3" (Butterfly) *
1 ea. Brass plate: 1"x 2-1/4 in (to mount SO-239, Gamma rod) *
1 ea. Copper strip 3/8 x 4" to make Gamma tube bracket *
1 ea. 3/4 CPVC TEE
3 ea. 3/4 to 1/2 CPVC reducer
Odds and Ends :
1 ea. 11" piece of RG8 insides (center conductor and insulation, Discard shield and outer plastic) *
1 ea. SO-239 coax connector (with tapped mounting holes and center pin) *
1 Lot Stainless Steel and Brass screws and Hardware *
Glue two of the 12.5" pipe sections into the CPVC reducers first, then glue the reducers into the opposite sides of the CPVC TEE. Lay the assembly on a flat surface with the center opening of the TEE facing the middle of the antenna. This is where the first 27" piece (mounting bar) goes in, via a reducer. On the outside edge of the CPVC TEE is where the butterfly attaches. For mobile or portable use, use 3 s.s. #6 screws through each of the CPVC TEE joints for added strength. The rest of the antenna solders together to form a square, using the 90 degree elbows at the corners. Drill small weep holes in the bottom corners of all four 90s to let accumulated water drain out.
The brass plate is bent to form an "L" 1-3/4" tall with a 1/2" lip. A 5/8" hole is provided 1-1/4 inch from the bend, and an SO-239 is attached . Two small holes are drilled in the lip and the plate is mounted to the copper TEE with s.s. #6 self taping screws. Attatch the center conductor of a 11" piece of RG8 insides to the center pin (center wire and plastic dielectric only- remove and discard shield and outer covering). This is accomplished by soldering or using a screw if the SO-239 has a threaded center pin *. Slip the other end of the RG8 insides into the 3/8"copper tube 10.5", and tap the copper tube to the radiating element 13-1/2" from the SO-239 center, with the Gamma tube bracket.
The tap on the Gamma sets the
impedance presented to the feedline. Resonance (center frequency)
is adjusted by turning the butterfly.
Mount 15 feet or more high, for home use, and wherever you can for mobile. An antenna like this can be mounted 3" to 6" above the roof of a vehicle using CPVC , PVC or acrylic spacers with suction cups.
Have fun on 6. Geo>K0FF
*Parts available in a kit from author, includes all "*" parts, drilled, punched, bent, and threaded, contact: K0FF@ARRL.NET
Don't Eat the Batteries" clause:
Recently my wife and I bought a new TV set, and in the instructions for the hand held remote control the warning said "Don't Eat the Batteries".
WARNING!!! This is antenna is an electrical conductor. Contact with power lines can result in death or serious injury. Do not install this antenna, supporting mast or tower structure near any power lines, or where they could come into contact with power lines should the antenna or structure fall.
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