CUSHCRAFT LFA-6M4EL Manuale utente

CAUTION: Read All Instructions Before Operating Equipment

308 Industrial Park Road

Starkville, MS 39759 USA

Tel: 662-323-9538 Fax: 662-323-6551

VERSION 1A

LFA-6M4EL

6 Meter 4 Element Loop Feed Antenna

INSTRUCTION MANUAL

Cushcraft

Amateur Radio Antennas

Cushcraft

Amateur Radio Antennas

GENERAL DESCRIPTION

UNPACKING

Unpack the antenna and check the parts against the Parts List and the drawings. This will simplify

the antenna assembly. Parts have been separated when possible to aid in assembly. Make sure you

have the necessary room to assemble the antenna before unpacking. This antenna will be very large

when finished. Try to assemble it in a large open area clear of obstructions and people. A driveway and

a couple of saw horses or other means of support will make it easy to handle the antenna when putting

it together. Assembly over grass is not recommended. There are lots of small things that can get lost

forever in grass. Some parts may have extras included so don’t worry if you have some left over when

your done. The design of the antenna makes it very easy to assemble.

Tools you will need

WARNING

WHEN INSTALLING YOUR SYSTEM, TAKE EXTREME

CARE TO AVOID ANY ACCIDENTAL CONTACT WITH

POWERLINES OR OVERHEAD OBSTRUCTIONS.

FAILURE TO EXERCISE THIS CARE COULD RESULT

IN SERIOUS OR FATAL INJURY

The LFA (Loop Fed Array) Low-Noise Yagi is very different from the traditional dipole fed Yagi in many ways

with its primary benefit being unwanted noise rejection. The LFA has a rectangular shaped, full wave loop

driven element that is laid flat on the boom between and in-line with the parasitic elements . Then there is the

way in which the loop functions. The smaller end sections which run parallel to the boom, are engineered to be

180 degrees out-of-phase with each other. This provides the same effect as is seen within ladder-line feeder; each

side cancels the other out and therefore, minimum radiation occurs. In practice this translates to highly

suppressed side lobes and side-on signal rejection. This feature also plays a role in reducing F/B (Front to Back

ratio), F/R (Front to Rear ratio) and broad-banding of the antenna too. It is these attributes which help give the

LFA class-leading all-round performance at almost any boom length and for any given band.

Tape measure in inches. A tape measure in feet and inches will do but you will have to convert.

7/16 wrench and/or nut driver

½ inch wrench

Phillips screwdriver

Flat head screwdriver for hose clamps

Assembly of the Boom

Assembly Instructions

Select the boom-to-mast clamp, (385142-1)

the boom-to-mast bracket (385144-1) and

four (4) 1/4" - 20 x 3/4" bolts (505266)

four (4) internal lockwashers (562961)

and four (4) 1/4" hex nuts (554099)

Place the boom-to-mast bracket (385144-1)

on the boom-to-mast clamp (385142-1)

align the holes and place the bolts in the

four (4) outer holes as shown in Figure 1

Select the two sections of boom (Front and

Rear), and insert them into the boom-to-mast

bracket until they meet at the center. Tighten

the bolts.

Install the U-bolts using the 5/16 nuts (555747)

385142-1

385144-1

562961,554099

and the 5/16 split washers (564792).

555747

564792

540067

Long tube ( 85 inch)

Short tube ( 75 inch)

Front of antenna

You may place the boom on a temporary mast or support it from each end.

This will make assembly and measurements easier. Find a location that is

suitable for an antenna this large. A concrete driveway is a good place to

assemble antennas. Any hardware you drop in grass may be gone forever.

Some of the smaller hardware has extra pieces just in case they are dropped.

170415

170413

190002 installed

on all brackets

5/8 x 7-1/2 tube

Assemble the brackets as shown in Figure 2 and

locate them on the boom assembly as shown in

Figure 3. It is easier to assemble the brackets on

the boom at the correct location, rather than try

to slide them on the boom. If you are going to

leave this assembly unattended for more than 15

minutes, we suggest that you tighten the eight

(8) bolts on each bracket, so that they do not

vibrate off. Do not tighten the anchor bolts on the

elements until the elements are completely

installed and aligned. Mark the bracket location on

the boom with a marker at the edge of the bracket

instead of the center. This will ensure the mark is

still visible when the bracket in is the correct spot.

Start from the rear of the boom and work forward.

The measurements are given in total inches from

the rear of the boom. If you need the distance from

each element to the next you may subtract the bracket

measurements to obtain this value. Total distance

is given for better accuracy in element placement.

Distance between elements measurements will cause

cumulative errors as each element is placed.

1/4-20 x 3/4

10-24 x ½

1/4-20 x 3/8

10-24

1/4-20

Square

1/4-20

1/4

#11 or #1 Bracket

5/8 Insulator on

#1 bracket only

#11 bracket

461057

190002

Insulator

170410

Inches from rear of boom

to back of bracket

2”

26-1/2”

44-3/4”

91-7/8”

156-1/4”

Figure 2

Insert all the way.

Tube should touch boom

Install boom caps

#1 bracket

#11 bracket

Figure 3

Slide the tube all the way into the bracket

until it just makes contact with the boom.

On the #1 bracket, insert it all the way into

the insulator.

Front of antenna

10-24 x ½

1/4-20 x 3/8

The #1 bracket uses 1/4-20

hardware for lock bolts.

53-3/8 INCHES

55-1/4 INCHES

48-3/4 INCHES

59-3/4 INCHES

174865 7/16 x 48 inches

174869

172922 7/16 x 47 inches

175512-1 7/16 x 42-3/4 inches

172928 7/16 x 53 inches

Instal the tubing in the locations shown.

The tubing can be identified by the lengths

given on the left side of the diagram.

This is the total length of the tube.

The element lengths are given from the

center of the boom to the tip of the tube.

For the driven element, the distance is

from the center of the boom to the outer

edge of the loop end. Slide a #4 hose

clamp over the loop ends before installing.

Verify the measurements and tighten the

clamps on the reflector and directors.

Leave the clamps on the loop end loose.

The loop end needs to move for final tuning

of the antenna. Install the 7/16 tube caps

on the ends of the elements.

Loop End

Don’t tighten loop clamps

until final tuning is done

#4 hose clamp

on each element

175512-1 7/16 x 42-3/4 inches

Front of antenna

Loop End

Slide the loop ends

into the tube evenly

so they do not bind.

Don’t tighten the

hose clamps until

tuning is finished.

Place hose clamp

over slot in tube

FEED LINE CONNECTION

#10 lockwasher

171329

10-24X1

Element

10-24 nut

Center

Conductor Shield

Connect your feed line as shown in the

diagram. One side of the driven element

is connected to the center conductor of the

coax and the other is connected to the shield.

Route the conductors so that they do not

touch the #1 bracket. Seal the

Coax where the conductors split

using an appropriate sealant.

Water should never be allowed

to enter the coax conductor. Use of

a balun is recommended. An example

of a coaxial balun is shown below. You

may use this method or any commercial

version you wish. Placement of the balun

does not have to be at the mast. It is better

to have it close to the feed point

RF Choke: 12 turns of

RG-8/U with a six inch

diameter.

Tape

It’s okay to spread the clamp

to install onto the 5/8 tube.

Mast

FINAL TUNING

Start by making sure the distance from the loop end to the center of the boom on one side

is the same as the distance on the other side. These distances must be the same. If you move

one, you must move the other. The antenna will not tune correctly if these are not the same.

The antenna must be at least 10 feet off the ground for initial tuning. Mount the antenna on a

temporary mast or other support when checking the SWR

Check the antenna using a SWR analyzer or radio with a good quality wattmeter that

indicates SWR. The antenna should have a SWR dip at or around 50.125 MHz . If you

do not see a dip at all, check all your connections and try again. If the dip is too low in

frequency, then the loop ends should be moved in toward the boom. Remember to move

both sides the same amount. Move them a small amount each time and recheck the SWR.

The dip point should move up as you move the loop ends in toward the boom. Continue

this adjustment until the frequency you desire has the lowest SWR. If the frequency is too

high then move the loop ends out away from the boom in the same manner. Do not tighten

the loop clamps each time you adjust the distance. The loop ends should have enough

friction to remain where they are without the clamps. When your happy with where the

antenna is tuned, then tighten the clamps.

SAME SAME

Your antenna is now ready for mounting. This antenna is large and too much for one

person to handle. Make sure before you start that you have everything you need and

a friend to help with the installation. Do not attempt to install the antenna alone. Do

not install the antenna in a location where it can come into contact with electrical lines

or any location it could possibly fall into electrical lines.

Mast

NOTES

Indice

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