DX Engineering DXE-SWA-070 Manuale utente

Linear-Loaded Multi-Band Dipole

Patent Pending

DXE-SWA-070 Revision 3

©DX Engineering 2005

P.O. Box 1491 · Akron, OH 44309-1491

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

Fax: (330) 572-3279 · E-mail: DXEngineering@DXEngineering.com

Table of Contents

Introduction

Features 2

Mounting Considerations 2

Installation

Feedline 3

Feedline Length Calculator 4

Assembly

Cenetr T Support 5

Support Line 5

Antenna Conenctions 6

Wire Element Connections 6

End-Insulator Connections 7

Tuner Connections 7

Tuning Addendum 7

Optional Accessories 9-10

Technical Support and Warranty 11

- 2 -

Introduction

The DX Engineering Linear-Loaded Multi-Band Dipole (Patent Pending) is a 74 ft,

lightweight yet rugged design that is usable with a tuner from 3.5 to 30 MHz. It’s ideal for

portable or tactical use and can be easily installed in attics, small lots or Covenant Condition

Restricted locations.

Features

•Linear-loaded elements for the lower bands reduce wingspan over a dipole

•High efficiency design gives dipole-like performance

•No traps or coils

•3.5 to 30 MHz continuous coverage

•Correct design makes it easily tuned

•Well-designed feedline reduces noise pickup over Windom types.

•Insulated Elements and stainless hardware

•Unique support line combats heavy ice loading

•Black UV color ideal for concealment

The Linear-Loaded Multi-Band Dipole kit includes multi-wire elements which are covered with

a flat-black, lightweight UV-resistant material, custom molded high impact center-T support and

end-insulators, 100 feet of premium ladder feedline and 100 feet of double-braided UV-resistant

Dacron mounting rope. Stainless steel hardware is used for all connections.

The DX Engineering Linear-Loaded Multi-Band Dipole can be used successfully with the balun

incorporated in most high quality antenna tuners to obtain a low SWR across the entire

frequency range. Using an external current balun may provide better performance and permits

converting to coax prior to entering the operating position which will reduce RFI.

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.

Generally speaking, these antennas should be mounted as high as possible for best performance.

Antenna height will affect the exact resonance point, radiation pattern, and takeoff angle. The

higher the antenna, the lower the takeoff angle to the horizon, which increases the effective range

of the antenna.

For DX, the minimum height above ground should be 1/2- to 1-wavelength at the lowest

operating frequency. On the low bands, this height becomes impractical for most hams. For

example, an 80m dipole at 70 feet is about 1/4-wavelength above the ground. This antenna

would be good for local and short distance communications, but not optimal for DX, due to the

high takeoff angle and ground absorption. A 40m dipole at 70 feet is approximately

- 3 -

1/2-wavelength high and is likely to be good for DX and less optimal for local or short range

communications. For more information on antenna design, feedline and radiation angles, consult

a reliable text such as the ARRL Antenna Book.

The antenna, including the 300 Ωfeedline, 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, metal in particular, within the near-field radiation pattern can

affect the impedance and radiation pattern of the antenna. 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.

Installation

You should have two rolls of element wire, one 100 foot roll of ladder feedline, and a hardware

packet. Unroll the 2 wire elements and feedline using a hand-over-hand technique. This will

prevent kinks and allow the wires to lay flat.

Feedline

The DX Engineering Linear-Loaded Multi-Band Dipoles include 100 feet of high quality 300 Ω

ladder line. Depending on your specific installation, this feedline will need to be shortened or

lengthened.

The feedline must be in odd multiple lengths of 1/8-wavelength on the lowest operating

frequency, in this case 3.5 MHz, to optimize the impedance presented to the balun over the

frequency range of the antenna. This length can be calculated using the following formula or use

Table 1. The DX Engineering 300 Ωladder feedline has a VF of 0.88.

Formula:

123 / Freq (MHz) x VF: Multiply the result times the ODD multiple (1, 3, 5, 7, etc) to get

the correct length closest to your required feedline length.

Where:

123 = 1/8-Wavelength Factor

Freq = Frequency in MHz

- 4 -

VF = Velocity Factor of Feedline

Lowest Frequency on which the

Antenna Will be Used (MHz)

Make Feedline an ODD Multiple of This Length in

Feet (1, 3, 5, 7, etc.)

VF is 0.88 (DX Engineering 300 Ωladder)

3.5 30.9

7 15.4

10.1 10.7

14 7.7

18 6.0

24.9 4.3

28 3.9

Table 1: 1/8-Wavelength Feedline Calculator

If you have excess ladder line, it can be zigzagged while suspended in air, but it can't be closer

than a few conductor widths to metallic objects and should not be coiled. If it is necessary to

pass closely to a metallic object, twist the line to partially balance the effect on both sides of the

feedline.

If you need additional feedline, 100 foot rolls of 300 Ωfeedline (DX Engineering part number

DXE-LL300-1C) and a convenient line coupler (part number DXE-LLC-1P) are available. This

coupler includes a high impact, insulated splice block, ring terminals and stainless hardware,

permitting strong and consistent splices of ladder line. See Figure 1.

Note: If using an external balun, the feedline length should be calculated to the balun.

Figure 1: Ladder Line Coupler

The wire elements are precut to the correct length and should not be trimmed.

- 5 -

Example: To use this antenna from 80m to 10m, the feedline should be in odd 1/8-wavelength

multiples on 80m. The 80m band starts at 3.5 MHz. Therefore, 123/3.5=35.1. Our feedline

VF=0.88, so 35.1 x 0.88=30.9 ft. per 1/8-wavelength. If 90 feet is needed to get to our operating

position, the nearest odd multiple 1/8-wavelength length is 92.7 feet. (30.9 x 3). If we needed 110

feet, we would have to add to the feedline to achieve 154.5 feet (30.9 x 5) to maintain the odd

1/8th multiple-rule for length

Assembling the Dipole

Center-T Support

The center-T support has pre-drilled holes for attachment of the wire elements, feedline and

support rope.

Support Line

The center-T support’s top hole is used for the attachment of a messenger line that is used to

provide support for the antenna wire and feedline. The use of the messenger line, which is

strongly recommended, will reduce the stress on the element wires and keep the antenna from

stretching over time, which will change its resonant frequency.

Ideally, the messenger line should attach to the same structure used for the dipole, only above it,

forming at least a 30 degree angle between the dipole and the messenger line to support the

antenna. See Figure 2.

Figure 2: Example Mounting Diagram

The included Dacron rope should be used for the messenger line by forming a loop at the mid-

point of the rope. Push this loop through the center-T support top hole, then pull the rest of the

rope through the loop. See Figure 3.

- 6 -

The excess rope can be used to attach the antenna end-insulators to the support structures. Use

the same structures used by the messenger line if possible. The ends of the rope should be

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

Connections

Install hardware on the center-T support as shown in Figure 3. Where the feedline and wire

element connect, use the star washer between the lugs as shown in the inset. Star washers are not

used for the other connections.

Figure 3: Assembled Center Support Bracket

Wire Elements

The multi-wire elements must be connected exactly as shown in Figure 3 for the antenna to

work properly. Locate the ends of the wire elements marked with red tape. These ends connect to

the center-T support. With the DX Engineering Logo on the center-T support facing up, feed this

element wire down through one side of the notched slot of the center-T support. Next, route the

element wire back up through the inner slot and attach the red wire lug to the lower left terminal.

This terminal will also be used for the feedline connection.

The black and white wire lug is connected to the top terminal on the center-T support. Repeat the

same process for the opposite side wire element. Excess slack in the wire elements on the center-

T support should be removed prior to putting up the antenna.

Feedline

With the DX Engineering logo facing up, the feedline should be routed down through the lower

slot, then back up through the upper slot, leaving just enough slack to permit making connections

to the lower terminals on the center-T support.

- 7 -

Red Ta

Connection to the End-Insulators

Install hardware and wire element ends as shown in Figure 4.

Figure 4: Assembled End Bracket

With the DX Engineering.com lettering facing down, and the notched edge of the end slot facing

up, route the wire down through the notched end slot, back up through the next slot, down

around the bracket and back up through the slot between the mounting hardware. Make the

terminal connections placing both wire lugs on the bolt assembly. Repeat for the opposite side.

Use the supplied Dacron rope to attach the end brackets to a suitable mounting point using a no-

slip knot such as depicted in Figure 5.

Figure 5:Suggested Knot for End Brackets

Connections to the Tuner

If routing the ladder feedline to the operating position and your tuner, keep the feedline in the

shack as short as possible and away from metal chassis or cabinets to prevent interaction and

unwanted RFI. Connect the ladder feedline to the balanced, two-terminal inputs on your tuner.

- 8 -

External tuners typically have inexpensive built-in 4:1 voltage baluns to convert the balanced

feedline to unbalanced, allowing the use of 50 Ωcoax for connection to your rig. Current baluns,

rather than voltage baluns, are a much better choice. Current baluns provide better balance,

almost always have lower loss, and tolerate load impedance and balance variations much better

than voltage baluns. To use a current balun, you will probably have to use one that is external to

the tuner.

Using an external current balun has a few advantages. By converting the ladder feedline to coax

away from the operating position, there is no unwanted feedline radiation in the shack. Reduced

noise and improved efficiency of the dipole will result and the structural proximity

considerations of ladder feedline can be greatly reduced or eliminated.

A high quality 4:1 current balun is ideal for this antenna and is available from DX Engineering

(part number DXE-BAL200-H10-AT). This balun provides better balance, often has lower loss,

and is more tolerant to load impedance and balance variations than most internal tuner baluns.

Use Table 1 to ensure the ladder feedline is in odd multiples of 1/8-wavelength before

connecting to the balun. Use a good quality coax, such as Belden RG-213, from the balun to your

tuner.

Internal tuners may not have the operating range to tune this dipole on every band; therefore, use

of an external tuner may be needed.

- 9 -

o…

…

- 10 -

DX Engineering Current Baluns

•5, 10 and 10 KW+ Baluns and Current Chokes

•High efficiency, low loss—W8JI design

•All ratios available

Feedline Current Chokes

•Reduce RFI and pattern distortion

•Prevent feedline radiation

Indice

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