"Editor's Note: Due to the popularity of some of eHam's older articles, many of which you may not have read, the eHam.net team has decided to rerun some of the best articles that we have received since eHam's inception. These articles will be reprinted to add to the quality of eHam's content and in a show of appreciation to the authors of these articles." This article was originally published on: 9/14/2000

Characteristics:

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), and 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 another 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.

Description:

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.

Mounting:

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.

Construction:

Material:
1/2" Copper waterpipe :
3 ea. 27 inch piece
4 ea. 12.5 inch piece

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 *

4 ea. Copper 90 Degree elbow
1 ea. 3/4 CPVC TEE
3 ea. 3/4 to 1/2 CPVC reducer
1 ea. Copper TEE
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 #6 s.s. 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.

*Parts are available in a kit from author which includes all "*" parts, drilled, punched, bent, and threaded, Contact George @ 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".

SO:

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.

Geo K0FF