DX Engineering DXE-OCF-KIT Manuale utente

Page - 1 -

Multi-Band

Off Center Fed Dipole Kit

DXE-OCF-KIT

DXE-OCF-K-INS Rev 0



DX Engineering 2023

1200 Southeast Ave. - Tallmadge, OH 44278 USA

Phone: (800) 777-0703 ∙ Tech Support and International: (330) 572-3200

E-mail: DXEngineering@DXEngineering.com

Page - 2 -

Introduction

The Off Center Fed dipole (OCF) is made up of two different lengths of antenna wire (dipole legs) for

operation on multiple bands. This manual will

show four versions of the Off Center Fed

dipole that can be made from this kit.

One concern with making a multiband OCF

dipole is achieving reasonable impedance on all amateur bands. As frequency increases the length of the

antenna and offset of the feedpoint become critical. Along with critical length and height above ground the

OCF is sensitive to anything in the surrounding area of the antenna. The versions described in this manual

were assembled, installed and tested in an area where there was no interference from other objects (trees,

fences, sheds, etc.). The analyzer scans are included for reference.

Dipoles are one of the best low-cost antenna options available for Amateur Radio use. They are easy to

construct, install and provide reliable communications. Having been a proven style of antenna for decades,

the OCF dipole antenna will get you on-the-air from your home QTH or in a portable operation area. For

more details on antenna design, feedline and radiation angles, consult a reliable text such as the “ARRL

Antenna Book”(https://www.dxengineering.com/parts/arr-1113).

The DX Engineering Multi-Band Off Center Fed Dipole is designed to be rugged yet lightweight. The kit

includes two lengths premium 14 gauge relaxed PVC antenna wire with a ring terminal soldered on one end,

one DXE-MC20-C4-1 DX Engineering Maxi-Core®4:1 Dual Core Balun, the DXE-WA-BMB Mounting

Bracket (US Patent No. D744,459) for Maxi-Core®Balun including End Insulators (US Patent No.

D534,905) and stainless steel hardware.

On most of the bands, the internal tuner on modern transceivers will be able to fine tune the antenna when

the SWR is 3:1 or less. On the bands that may be above 3:1 SWR, an external tuner may be needed.

Multi-Band Off Center Fed Dipole

Antenna Kit

Part Number

Antenna Wire

Package

(included)

Antenna Wire Description

Pre-Assembled, Crimped and Soldered 0.250 inch Ring Terminals, 14

AWG Stranded Copper, UV Black Relaxed PVC Insulation

Balun

(included)

Mounting Bracket

(included)

DXE-OCF-KIT

DXE-ANTW-OCF

Antenna Wires, Pre-Assembled, Crimped and Soldered 0.250

in. Ring Terminals, 14 AWG Stranded Copper, UV Black

Relaxed PVC Insulation, Ea. 48’ & 113’, Each

DXE-MC20-C4-1

4:1 Dual Core

DX Engineering

Maxi-Core®Balun

(with instruction

manual)

DXE-WA-BMB

Mounting Bracket for

Maxi-Core®Balun

includes End Insulators

(with instruction manual)

Kit includes instruction manual: DXE-OCF-K-INS

Page - 3 -

Features:

The DX Engineering Off Center Fed Multi-Band Dipole is built using the highest quality components.

Antenna Wire - 14 AWG stranded copper, black relaxed PVC jacket for flexibility and strength. Two

rolls of wire. The length of one roll is 48 feet (14.63m). The length of the other roll is 113 feet

(34.44m).

Wire Antenna Balun Mounting Bracket (US Patent No. D744,459) - made from a super high-strength

UV resistant black poly-resin compound.

End-insulators (US Patent No. D534,905) - made from a super high-strength UV resistant black poly-

resin compound.

Balun Mounting Bracket and End Insulators use an exclusive serpentine wire-weave grip for insulated

antenna wire. This method of threading the wire provides a grip strong enough to permanently support

the antenna wires. This allows fast and easy field adjustments of antenna length for tuning.

Hardware - Stainless steel.

Power rating - Up to legal limit of 1.5 kW when using the included DX Engineering DXE-MC20-4-1

Maxi-Core®20 Balun. As with any antenna, care should be taken when operating the digital

modes such as FT4 and FT8. These modes are inclined to be hard on antenna and transceivers.

Any power rating mentioned for any antenna should be lowered to 25% when using the FT4,

FT8 and other high rate modes.

Off Center Fed Dipole versions

The four versions that were assembled and tested by DX Engineering are:

Version

Radiating Wire Lengths

Total Overall

antenna length

Bands

94 feet (28.65m)

40 feet (12.12m)

134 feet (40.85m)

90 feet (27.43m)

45 feet (13.71m)

135 feet (41.15m)

110 feet (33.53m)

28 feet (8.53m)

138 feet (42.06m)

57 feet (17.37m)

12 feet (3.66m)

69 feet (21.03m)

The SWR measured on the tested antenna versions:

Version

Radiating Wire Lengths

Total Overall

antenna length

SWR (x:1) Measured on Bands

94 feet (28.65m)

40 feet (12.12m)

134 feet (40.85m)

1.2-4

1.8-2.5

4.5

1-8-2.5

2.5

3.2

1.2-2.8

90 feet (27.43m)

45 feet (13.71m)

135 feet (41.15m)

1.8+

<1.5

<1.2

1.2-2.5

110 feet (33.53m)

28 feet (8.53m)

138 feet (42.06m)

2.5

1.8

1.7-2.5

1.2-3

57 feet (17.37m)

12 feet (3.66m)

69 feet (21.03m)

<2.5

<1.8

1.2-2.5

Page - 4 -

The two antenna wire lengths that are included in the kit are 113 feet (34.44m) and 48 feet (14.63m) in

length. These lengths are trimmed (as needed) for the version that you are building.

Version

Radiating Wire Lengths

Total Overall

radiating antenna length

Bands

Leg 1

Leg 2

94 feet (28.65m)

40 feet (12.19m)

134 feet (40.85m)

80/40/30/20/17/15/12/10

meters

Cut Wire Lengths

97 feet (29.97m)

43 feet (13.11m)

Version

Radiating Wire Lengths

Total Overall

radiating antenna length

Bands

Leg 1

Leg 2

90 feet (27.43m)

45 feet (13.72m)

135 feet (41.15m)

80/40/20/17/15/12/10

meters

Cut Wire Lengths

93 feet (28.35m)

Do not cut use entire

48 foot length

Version

Radiating Wire Lengths

Total Overall

radiating antenna length

Bands

Leg 1

Leg 2

80/40/30/20/15/12/10

meters

110 feet (33.53m)

28 feet (8.53m)

138 feet (42.06m)

Cut Wire Lengths

Do not cut use entire

113 foot length

30 feet (9.14m)

Version

Radiating Wire Lengths

Total Overall

radiating antenna length

Bands

Leg 1

Leg 2

57 feet (17.37m)

12 feet (3.66m)

69 feet (21.03m)

40/20/15/10

meters

Cut Wire Lengths

60 feet (18.29m)

15 feet (4.57m)

Page - 5 -

Required Items not included in Dipole Kits

Rope

Choose the type of rope you desire in the total lengths required for: both ends of Dipole to the Dipole Supports,

Guy Ropes (as needed), and center support Messenger Line length (if used). Lengths will vary with customer’s

installation configuration and requirements.

Synthetic Textile Brand: You can search the DX Engineering website for “Synthetic Textile Rope”or use this

link: https://www.dxengineering.com/search/part-type/rope?fr=part-

type&SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=syn

-OR-

Mastrant Brand Rope: You can search the DX Engineering website for “Mastrant Rope” or use this link:

https://www.dxengineering.com/search/part-

type/rope?N=brand%3Amastrant&SortBy=Default&SortOrder=Ascending&keyword=rope&kr=rope

Center Support and End Supports

Fiberglass Pole Kits: You can search the DX Engineering website for “Fiberglass Pole Kits” or use this link:

https://www.dxengineering.com/search?N=brand%3Adx-engineering%2Bpart-type%3Afiberglass-tubing_tubing-

compression-clamp-kits_fiberglass-tubing-

kits&SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=FIBERGLASS%20POLE%20KITS

Carbon Fiber Pole Kits: You can search the DX Engineering website for “Carbon Fiber Pole Kits” or use this

link: https://www.dxengineering.com/search/brand/dx-engineering/part-type/telescoping-masts?fr=part-

type&SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=CARBON%20FIBER

JTL-12555 Jet Lube SS-30 compound: You can search the DX Engineering website for “Jet-Lube SS-30” or

use this link: https://www.dxengineering.com/search?N=part-type%3Aanti-

seize&SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=jet-lube%20ss-30

Used on the threads of Stainless Steel Hardware to prevent galling (seizing)

Additionally:

One Studded Element Clamp and two #10 x .6875, 11/16” OD Fender Washers 0.37” thick for

mounting the Balun Mounting Bracket to your center fiberglass pole - See page 10 for details.

Electrical Tape

Use of the DX Engineering Coaxial Connection Weatherproofing Kit DXE-WPCC88-1 is recommended for

weatherproofing the coax cable connection at the Balun.

Page - 6 -

Safety Considerations WARNING!

INSTALLATION OF ANY ANTENNA NEAR POWER LINES IS DANGEROUS

Warning: Do not locate the antenna near overhead power lines or other electric light or power circuits, or

where it can come into contact with such circuits. When installing the antenna, take extreme care not to

come into contact with such circuits, because they may cause serious injury or death.

Overhead Power Line Safety

Before you begin working, check carefully for overhead power lines in the area you will be working. Don't

assume that wires are telephone or cable lines: check with your electric utility for advice. Although overhead

power lines may appear to be insulated, often these coverings are intended only to protect metal wires from

weather conditions and may not protect you from electric shock. Keep your distance! Remember the 10-foot

rule: When carrying and using ladders and other long tools, keep them at least 10 feet away from all

overhead lines - including any lines from the power pole to your home.

Mounting Considerations

When planning the location of your antenna, consideration should be given to the height, location of suitable

support structures and feedline positioning and length. The OCF dipole antenna should also be mounted as

far from other structures as possible. This includes the ends of the wire elements, which are actually the most

sensitive part of the antenna. Any objects, tree limbs, foliage, metal in particular, within the near-field

radiation pattern can affect the impedance and radiation pattern of the antenna.

NOTE: The four OCF antenna versions described in this manual were installed, tuned and tested

using three fiberglass poles. The center pole was 35 feet (10.67m) high. The dipole leg support poles

were 8 feet (2.44m) high. The location used was clear of any close by trees, fences and any other

objects.

Variations in antenna height and location in reference to other nearby objects will affect the exact

resonance point, radiation pattern, and takeoff angle. Your results may vary.

For more information on antenna design, feedline and radiation angles, consult a reliable text such as

the “ARRL Antenna Book”. (https://www.dxengineering.com/parts/arr-1113)

The feedline should also come away from the antenna at right angles for at least 1/2-wavelength for best

performance.

Most installations involve compromises due to local terrain, available supporting structures, or other

restrictions. Do the best you can with what you have and be aware that your SWR measurements and your

results may vary.

Page - 7 -

Assembling a Off Center Fed (OCF) Dipole

Center-T and Balun Support

The patented (US Patent No. D744,459) DXE-WA-BMB Center-T and Balun support has pre-drilled holes

for attachment of the wire elements and pre-drilled holes for a support clamps. Also included are the patented

(US Patent No. D534,905) End Insulators.

Qty

Parts List - DXE-WA-BMB

DX Engineering Balun & Wire Antenna Bracket

DX Engineering End Insulators

6-32 x 3/4” long Stainless Steel Hex Head Bolts

#6 Stainless Steel Flat Washers

6-32 Nyloc Hex Nuts

Using the included Stainless Steel Hardware, mount the included DX Engineering Maxi-Core®20 balun 4:1

Balun - part number DXE-MC20-C4-1 as shown below. Note: When installing stainless steel hardware, it is

highly recommended that JTL-12555 Jet Lube SS-30 be used to prevent thread galling.

Mount the Balun on the side opposite the cupped areas of the dipole wire guides.

Page - 8 -

Cutting Antenna Wire Lengths

The included antenna wire lengths that come with the DXE-OCF-KIT are:

One roll of antenna wire that is 113 feet (34.44m) in length

One roll of antenna wire that is 48 feet (14.63m) in length

Depending on which version OCF dipole you decide to make you will cut the long (Leg 1) antenna wire and

short (Leg 2) antenna wire accordingly.

Four Versions of the OCF dipole:

Version

Radiating Wire Lengths

Total Overall

radiating antenna

length

Bands

Leg 1

Leg 2

94 feet (28.65m)

40 feet (12.12m)

134 feet (40.85m)

90 feet (27.43m)

45 feet (13.71m)

135 feet (41.15m)

110 feet (33.53m)

28 feet (8.53m)

138 feet (42.06m)

57 feet (17.37m)

12 feet (3.66m)

69 feet (21.03m)

NOTE: In the following example - Version 4 OCF Dipole

covering 40, 20, 15 and 10 meters is being assembled and tested.

Note: Add approximately 3 feet (0.91m) to each end of the wires to allow

wrapping through the end insulator and tuning.

Version

Radiating Wire Lengths

Total Overall

radiating antenna length

Bands

Leg 1

Leg 2

57 feet (17.37m)

12 feet (3.66m)

69 feet (21.03m)

40/20/15/10

meters

Cut Wire Lengths

60 feet (18.29m)

15 feet (4.57m)

In this example (version 4 OCF dipole antenna) cut the long wire (Leg 1) to 60 feet (18.29m) and the short

wire (Leg 2) to 15 feet (4.57m)

By starting out with the longer lengths of each leg, you will be able to properly tune your antenna using an

antenna analyzer. It’s always easier to cut excess wire rather than having to solder on extra wire when

tuning.

Page - 9 -

Install OCF Dipole Wires to Balun

Route both OCF dipole wires through the Balun Bracket as shown.

Connect long wire (Leg 1) to the +side of the Balun (Red +and Red Din DX).

Connect the short wire (Leg 2) to -side of the Balun (Black -and Black Xin DX).

The Balun that is included in this kit is a current Balun and both sides will have equal current. You do not

have to connect the wires as shown - you can swap sides if you want to. The above connections make it a bit

easier to describe Leg 1 and Leg 2 lengths in this manual.

Install the round terminal rings between the two washers on the Balun and tighten in place.

Dipole Wires and End Insulators

The End Insulators are installed at the far ends of the dipole wires. One on each wire end. Route the dipole

wire in a serpentine manner as shown below. Note the wire enters the End Insulator at the cupped area.

At this point, do not cut the length of the dipole legs shorter. Wrap the extra length back on the dipole leg as

shown below. Since the wire insulation is a ‘relaxed PVC” and will unwind easily, use a piece of electrical

tape to hold the wrapped wire in place.

Once tuning is done, you can trim the wire as needed.

Page - 10 -

Attaching Rope to the End Insulators

Optional UV protected rope should be secured to the End Insulators (depending on your installation) using a

non-slip knot.

One suggestion for attaching the rope to the End Insulators is shown below. The ends of the rope should be

cauterized with a small flame to prevent the rope braid from fraying.

Non-Slip Knot using UV protected Rope

Antenna Supports

The center support used for the DX Engineering testing was a 35 foot (10.69m) fiberglass tube assembly and

the Balun Mounting Bracket was held to the top of the tubing using an optional studded element clamp

DXE-ECLS clamp (Element clamp with a welded threaded rod) using two fender washers (customer

supplied) through the hole at the top of the bracket.

Refer to the DX Engineering website to determine the ECLS Clamp size that fits the center pole that is used.

There is a chart that will help you determine the size ECLS clamp you require.

See: https://www.dxengineering.com/search?N=part-type%3Astudded-

clamps&SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=ecls%20clamp

Use the two fender washers (#10 x .6875, 11/16” OD

Fender Washers 0.37” thick) on each side

of the upper hole in the mounting

bracket. Install the threaded portion of

the ECLS clamp through the washers and

tighten in place. You can then install the assembly

on your pole and tighten the ECLS worm drive in place.

The lower portion of the Balun was held to the fiberglass pole by securing the feedline coax to the pole with

electrical tape.

The end supports, on the tested antenna, were two fiberglass poles 8 feet (2.44m) high. The ropes from the

ends of the antenna were tied near the tops of the poles.

Indice

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