CUSHCRAFT LFA-2M16EL Manuel utilisateur

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-2M16EL

16 Element Loop Feed Beam

For 2 Meters

INSTRUCTION MANUAL

111

Cushcraft

Amateur Radio Antennas

Cushcraft

Amateur Radio Antennas

GENERAL DESCRIPTION

UNPACKING

Unpack the antenna and separate the parts according to 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 long

when finished, don’t try to assemble it inside your house and then move it outside. A car garage with

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.

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.

BOOM IDENTIFICATION

Here are the 7 boom sections with measurements displayed for the pre-drilled holes. The numbers on top

are the distance in inches from the rear of the boom when it is correctly assembled. The numbers on bottom

are the distance in inches from one side of the individual tube. These numbers are to verify correct location

and orientation of each tube. Identify each tube by the color band on it. Once you have identified the tubes,

determine which end of the tube will insert into the middle boom section. Mark this side of the tube 3 inches

from the end. This mark will be used to set the insertion depth into the next size tubing. If the tubes are put

together incorrectly, the elements will be out of place and the antenna will not work properly. Use a sharpie

or other marking pen to draw a line on the tube.

THIS MARK IS INDEPENDENT OF THE IDENTIFICATION MARK

285.25 322

1-1/4 x .058 x 72

9.25 46

395.75

360.25

15.25 50.75

1-1/8 x .058 x 72

428.5

1.5

1 x .058 x 16

1-1/4 x .035 x 72

14.5

1.5 24.875 41.125 54.375

10.625 1-3/8 x .058 x 72

79.625 111

5.875 40.25

1-1/2 x .058 x 72 with

1-3/8 x .058 x 65 insert

143.875 178.25

213.25 249

6.25 42

1-3/8 x .058 x 72

Mark 3 inches from end

BROWN

RED

ORANGE

YELLOW

GREEN

BLUE

VIOLET

BOOM ASSEMBLY

1-1/4 x .035 x 72

1-3/8 x .058 x 72

1-1/2 x .058 x 72 with

1-3/8 x .058 x 65 insert

1-3/8 x .058 x 72

1-1/4 x .058 x 72

1-1/8 x .058 x 72

1 x .058 x 16

7Front of Antenna

Rear of Antenna

Place a #16 hose clamp over the tube before inserting next section

Feed Loop Assembly

To assemble the feed loop onto the boom you will need the following parts.

2 feed loop ends 1 long 7/16 tube

2 short 7/16 tube

1 insulator

8-32 x 1 bolt

8-32 x 2 bolt

8-32 nuts and lock washers

7/16 X 30

7/16 X 14-1/2

Insert each tube 3 inches into the next using the marks you made. Try your best

to align the holes in each tube. Tighten the hose clamps just enough so that the

tubes do not move. Final alignment of the tubes will likely be needed later. Now

would be a good time to support the boom on a couple of saw horses or something

similar.

Mount the insulator on the Boom at the second hole from the rear of the antenna using the 8-32 x 2

inch bolt. Attach the two short 7/16 tubes to the insulator using the 8-32 x 1 inch bolt thru the holes

in the ends of the tubes. Go ahead and tighten the nuts but do not crush the tubes.

Mount the long 7/16 tube to the third hole from the rear of the boom using a longer 8-32 x 2-1/4

bolt, half washer and element saddle.

8-32 x 2-1/4 half washer

element saddle

short tubes with insulator

Long tube with saddle

2 IN BOLT

2-1/4 IN BOLT

8-32 x 2

8-32 nut

#8 lock washer

8-32 nut

Element saddle and

half washer.

Rear of Antenna

7/16 X 30

7/16 X 14-1/2

Put one hose clamp over each end of each tube. Insert the loop ends into the 7/16 tubes.

Don’t force them. Keep them straight as they go in. Leave them loose for tunning the

SWR later. The tubes will have enough friction to stay without the hose clamps being

tightened.

INSTAL THE ELEMENTS

The Rod elements are labeled with color bands using the

standard resistor color codes. Starting from the rear of

the antenna, the first rod is R1 and the last rod is R13.

R1 is the reflector and R2 is the first director. A chart is

provided and the element colors are listed for each element.

Install them on the boom in the proper location using the

half washer, saddle and 8-32 x 2 inch bolts nuts and lock

washers. Because of different size boom sections, some

bolts need to be longer to mount the element. These bolt

lengths are listed on the next page.

8-32 x 2

8-32 x 2-1/4

8-32 x 2-1/2

half washer

element saddle

R3 R4 R5 R6 R7 R8 R9 R10 R11

R1 R2 R3 R4

R12 R13 R14 R15

BLACK 0

BROWN 1

RED 2

ORANGE 3

YELLOW 4

GREEN 5

BLUE 6

VILOET 7

GREY 8

WHITE 9

3/16 ELEMENT ROD LENGTHS

AND COLORS

R1 41.5 INCH BROWN (Reflector)

R2 37.9 INCH RED (Director #1)

R3 36 INCH ORANGE

R4 36.5 INCH YELLOW

R5 36.5 INCH GREEN

R6 36 INCH BLUE

R7 35.75 INCH VIOLET

R8 35.5 INCH GREY

R9 35.15 INCH WHITE

R10 34.5 INCH BROWN BLACK

R11 34. INCH BROWN BROWN

R12 33.50 INCH BROWN RED

R13 33.50 INCH BROWN ORANGE

R14 33.50 INCH BROWN YELLOW

R15 33.50 INCH BROWN GREEN

Once you have all the elements on in the correct location, check the alignment of the elements on the

boom sections. Element locations are given on the top of the diagram above. You may use this to verify

correct tube overlap between sections and that the booms are assembled correctly.

Rotate the sections to align the elements if needed and re-tighen the clamps.

Boom to Mast

Select the parts shown and install the mast plate onto the boom. The mast plate should be installed

on to the largest section of the antenna (boom section #3) . You may balance the boom

by installing the plate at the center of gravity of the antenna. You can determine this point

by simply holding the antenna and balancing it in your hand. Make sure the elements are in correct

orientation before tightening the U-bolts. Do not allow the mast plate to come within 1 inch of the

elements on that section.

401

119 118

401

84 85 104

404

326

85 010085

104 010104

118 010118

119 010119

401 010401

404 010404

70 190070

326 290326

010084

111

2”

2-1/4”

2-1/2

2”

2” 2” 2-1/4” 2-1/4” 2-1/4”

2-1/2 2-1/4”

2”

2” 2” 2” 2” 2”

Element Bolt Sizes

1.5

24.875

41.125

54.375

79.625

111

143.875

178.25

213.25

249

285.25

322

428.5

395.75

360.25

25-1/4 32-7/8 35 36-1/4 38-1/4 32-3/4

Tuning

Your antenna is now ready for tuning. Remove it from your assembly area and mount it on a temporary

mast at least 8 feet off the ground. Using a SWR analyzer or radio and SWR meter, check for

a dip in swr at or about 144.300 MHZ. You should see a dip in the SWR. If not, Check all connections

and retest. If the dip is too low in frequency, move the loop ends in toward the boom. Move each side the

same and keep them both the same distance from the boom. If the dip is too high in frequency, move the

loop ends out away from the boom. It is not necessary to tighten the clamps each time for tuning. Once

the dip is centered where you want it, tighten the clamps on the tubes. Do not use a wrench or powered

device to tighten the clamps. A nut driver or screwdriver is plenty to do the job.

Move out to shift frequency down

Attach your coax to the feed loop using the remaining 8-32 nuts and lock washers.

Make the distance of the exposed conductors as short as possible. Seal this connection

using a appropriate sealant to prevent water from entering the coax. Wind a choke balun

into the coax using a household cleaner or spray paint can. Put 3 turns around the can and

secure the coax together using cable ties. Attach the balun to the boom with tape and route

the coax along the boom to the mast and go down from there.

5/16 x 1-5/8

Chain link

1/4-20 x 1-5/8

5/16 split washer

5/16 hex nut

1/4 2 hex nt

- 0 u

1/4 2 locw asher- 0 k

Tape one end of the cable to the

chain link with electricians tape.

378216

583 Thb e

371 im l

168695 351244

Tape coax to boom

and mast when mounted

at its final loacation

The antenna is now ready for mounting on your pole or tower. Route the coax along the boom

and mast. Secure it using cable ties or electrical tape. Check the antenna over one last time to

make sure everything is in place and secure. If you haven’t already, place the plastic end caps

over the end of the booms. When installing the boom support, pull the rope tight. It may

stretch over time so you may compensate by adding about an inch of height to the ends of the

antenna over the mast mount. Un-screw the turnbuckles all the way and move the clamp up

and down to adjust the tension at first. Us the turnbuckles to make fine adjustments to the

tension. Don’t forget the thimbles on each end of the rope, they prevent the metal from cutting

through when the antenna moves.

12 element Antenna shown in vertical position

for Illustration only. Boom support clamps are

installed on the 1-1/4 inch end boom sections.

1/4-20 nut

1/4 lock washer

1/4 flat washer

turnbuckle

1/4 flat washer

1/4-20 nut

1/4 lock washer

1/4 flat washer

MAST

Thimble

358731

1-1/4 inch tubing

( last section )

Install the tube clamp at the last joint on each end

of the antenna. This will prevent the clamp from

slipping.

BOOM SUPPORT

Place support clamp about 3 feet above the

boom clamp. Use left over rope to prevent

turnbuckle from rotating after installation

by routing it through the eyelets. Pull the

rope tight and tie it off. You may use cable

ties or other means of securing the

turnbuckle if you wish.

024624

About 3 feet

Your U-bolt

may differ.

Tighten the U-bolt first an

then tighten the nuts holding

the turnbuckle.

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