CUSHCRAFT LFA-6M7EL Manual de usuario

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-6M7EL

6 Meter 7 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

Boom Insert

( 171541)

Assembly of the Boom

Slide the boom insert into boom ends, as shown

in Figure 1. Select the boom-to-mast bracket and

clamp parts. Loosely assemble them on the

boom ends.

Secure the boom ends and brackets together with

four (4) 1/4"-20 x 3/4" bolts, lockwashers and

nuts, and two (2) 5/16"-18 x 2 3/4" bolts, lock-

Tighten these six bolts securely. The casting-to-

boom bracket may deform slightly when the

four 1/4" bolts are tightened. This is normal.

Assemble the two cast aluminum brackets (1) on

your temporary mast at about 4 feet (1.2 m)

above ground. An eight foot length of 2" ABS or

PVC plastic drain pipe makes an inexpensive

temporary mast. Secure the two brackets

together using two (2) 5/16"-18 x 3" bolts,

lockwashers and nuts. Tighten these

two bolts evenly until the brackets are snug.

Note: If you use a galvanized 1-1/2

schedule 40 or 80 pipe as a mast, it

has an O.D. of 1.9”. You will need

to put two split lockwashers under

the 5/16 nuts on the four long bolts.

MAST ( Supplied by customer )

( 1.9” to 2.5” diameter )

5/16 x 5

102734

5/16x2-3/4

172732

1/4-20x3/4

172735

5/16x3

5/16x4

170424

175661170410

Secure using the 1/4-20 x 2-1/2 bolts

1/4-20 lock washer

1/4-20 nuts

170424

figure 1

156 1

7566

washers and nuts.

170424170424175661 170410

2”x 572”x 57 2”x 75 2”x 75

2”x 81 heavy

wall

2”x 81 heavy

wall

Assemble the boom as shown below. Use the

1/4-20 x 2-1/2 bolts, lock washers and nuts.

See figure 1

Boom is symmetrical (same on both sides)

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

1/4-20 x 3/8

1/4-20

Square

1/4-20

1/4

#12 or #13 Bracket

5/8 Insulator on

#13 bracket only

1/4-20 x 3/8

Figure 2

31-9/16

49-13/16

243-1/4

165

330-5/8

410

3 inches

Figure 3

#13 bracket

with insulator

#12 bracket

Inches from rear of boom

to back of bracket

Identify the element tubes by their total

length given on the left side of the diagram.

Instal the tubes in the locations shown.

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.

The loop will need to be adjusted for SWR

so this measurment is just a starting point.

Leave the clamps that secure the loop end

loose. There should be enough friction

between the tubes to keep them in place.

Verify the measurements on the elements

and tighten the clamps on the reflector and

directors. Do not overtighten the clamps.

They can be damaged if you use too much

torque. A nut driver or screwdriver will do

the job. Do not use a wrench or socket on

the clamps. A wrench will strip the threads

on the band. Install the 7/16 tube caps

on the ends of the elements.

174865

172922

49-1/2 INCHES

174869

175512-1

Loop End

Don’t tighten loop clamps

until final tuning is done

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

172928

Install boom caps

7/16 x 53 inches

7/16 x 48 inches

7/16 x 47 inches

58-3/8 INCHES

55 INCHES

53-1/8 INCHES

52-7/8 INCHES

51-7/8 INCHES

50-3/8 INCHES

The band may be

opened to place

the clamp on the

element tubing.

Nut Driver

Screw Housing

Slot Center the clamp

housing over the

slot. The housing

and slot can be

orientated in any

direction– Not

Necessarily UP

Band

5/16 x 1-5/8

Chain link

Turnbuckle

351243

1/4-20 x 3/4

5/16 split washer

5/16 hex nut

e n

1/4-20 h x ut

as1/4-20 lockw her

Make a sufficient number of wraps,

then wrap with electricians tape.

Tape one end of the cable to the

chain link with electricians tape.

82637 1

358731

378208 Place the clamp next to the

boom section bolt. This will

prevent it from moving.

358731

351244

Chain link

351244

Placement on the other side of the

1/4-20 bolt will prevent movement

Install the boom support cable as shown. You will need to cut the cable to the correct length.

30 feet has been supplied. Cut this length in half and use one for each side. To adjust tension

on the cables, slide the mount up and down to level the boom. Use the turnbuckles for fine

adjustment after the clamp has been secured. Make sure after your done adjusting to route

the wire as shown in the above diagram. Looping the wire through the turnbuckle will prevent

it from turning and releasing tension on the wire. You should have more support wire than needed.

The excess will depend on how high you mount the support bracket above the antenna.

Slide mount up and down to adjust

tension. Use the turnbuckle for fine

adjustment.

About 3ft

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 #13 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

3/4 5”

5-3/4”

To RF Choke

Coax Stripping

Mast

Boom

Example of Balun attachment

(not the same as your mount)

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.

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