KFFs Homebrew Tips

 

 

The 2 meter Square Copper Dipole by KFF

Originally published and copyright by KFF 5 Dec 2000 on eHam

 

Construction Detail

 

Here is the parts list and dimension sheet for a 2m square dipole, made from copper plumbing fittings and copper water pipe.

 

 

It is more or less omni-directional, and horizontally polarized.

You can even make it from the short pieces of pipe left over from the 6M project (see eHam how-to article 6 Meter Square Copper Dipole by KFF).

The antenna presents a low-through-high angle of takeoff, and is intended for use in the 144.200 area, although its wide enough to use as an AO-27 uplink, and can handle 100W. Its particularly useful on AO-27 when the pass is very high or overhead, and in the cone of silence of a fixed vertical. I use this for mobile satellite uplink, and wave a short hand-held 430 antenna out the window for receive. Excellent results from SSB mobile too, where Ive been able to talk to other mobiles similarly equipped 200 miles away. The mounting arrangement allows it to be affixed to a standard mobile mast that presents a 3/8 x 24 male thread (ALA Hustler base mast). You run coaxial cable right to the antenna and connect it to the built in SO-239.

The only adjustment on it is the Gamma match, as the design dimensions set resonance. You may want to adjust the final SWR by sliding the end caps in or out before soldering them.

BRASS PARTS

It's just a dipole folded around on itself.

The shape is an open 11 with mounting via a copper TEE 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.

For stacking a pair, you could make the TEE and threaded insert come horizontally instead, and mount one antenna above the other. (Future articles will give detailed info on stacking antennas in general). Stacked antennas provide improved gain and power handling capabilities.

Side mounting on a tower can be achieved by using conduit clip large enough to go around the mast (or tower leg), and run a 3/8 x 24 s.s. bolt into the threaded fitting.

Copper Parts

Solder the antenna parts together per the drawing using the 90

degree elbows at the corners. Cap the far (open) ends and mind the gap. All measurements are critical. The brass plate* to hold the SO-239 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 the SO-239 is attached using stainless steel or brass hardware*. Two small holes are drilled in the lip and the plate is mounted to the copper TEE with #6 s.s. Self-taping screws*. Solder a ring lug* to the center conductor of an 11" piece of RG8 insides* and screw it into the threaded coupling* on the SO-239 *(center wire and plastic dielectric only- remove and discard shield and outer covering). Slip the RG8 insides into the 3/8" copper tube* 4-1/2", and tap the copper tube to the radiating element 3-1/2 from the SO-239 center, with a copper strap bracket *.

The tap on the Gamma sets the impedance presented to the feedline.

Resonance (center frequency) is designed into the measurements.

 

 

PARTS PLACEMENT

 

Gamma Tap

Parts for Gamma, both 6 and 2 Meter Versions. Roll the tubing straight between two boards.

 

 

Materials List

copper water pipe:

2 ea. 3 ( capped end)

2 ea. 4 (TEE end)

2 ea. 9 (Sides)

 

4 ea. copper 90 degree elbows*

1ea. copper TEE*

1 ea. copper caps

 

5 of 3/8 copper refrigeration tubing ( Gamma Tube)*

6 of RG-8 insides with solder lug*

Brass Plate for Coax connector*

1 ea. SO-239 with Brass threaded insert*

1 ea. Brass rod, threaded for 3/8x24 for mast attachment*

1 ea. wide copper strip ( Gamma tube bracket)

Misc. stainless steel screws and hardware*

 

* Denotes kit items. Contact K0FF@ARRL.NET for availability

Kits include all parts, machined and punched ready for assembly, except the straight copper water pipe pieces. The 6 or 2 Meter kits are $18.00/ One or two kits can be sent via priority mail for $4.00

 

Nearly Complete

 

Have fun on 2. Geo>KFF

 

THE 6 Meter Copper Loop

 


Here is the parts list and dim. sheet for a 6m Square Copper Dipole, made
from copper water pipe.

Characteristics:

It is more or less omni-directional, and horizontally polarized.

 

Copper is the best possible electrical conductor at normal temperatures, next only 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 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.

 

INSULATOR:

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. Attach the center conductor of an 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.

 

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 : 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>KFF

 

The First 6M DXCC from Missouri

The Only Zero with 5BDXCC and endorsements for 160/17/12/6 Meters.