Cushcraft LFA-6M5EL User guide

Cushcraft

Amateur Radio Antennas

LFA-6M5EL

6 Meter 5 Element Loop Feed Antenna

INSTRUCTION MANUAL

VERSION 1A

CAUTION: Read All Instructions Before Operating Equipment

Cushcraft

Amateur Radio Antennas

308 Industrial Park Road

Starkville, MS 39759 USA

Tel: [phone] Fax: [phone]

GENERAL DESCRIPTION

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.

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

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

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

2

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, lock­washers and nuts.

Tighten these six bolts securely. The casting-to­boom 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.

5/16x4

5/16x3

1

7

66

5

5/16 x 5

1

figure 1

102734

5/16x2-3/4

1

6

56

7

1

172732

1/4-20x3/4

172735

MAST ( Supplied by customer )

( 1.9” to 2.5” diameter )

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.

170410

175661

Boom Insert

( 175667)

See Figure 1

175661

Secure using the 1/4-20 x 2-1/2 bolts
1/4-20 lock washer
1/4-20 nuts

175661

175661

170410

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.

Inches from rear of boom
to back of bracket

91”

31-1/4”

49-1/2”

Install boom caps

4”

#12 bracket

190002

170410

#13 bracket

#12 bracket

Insert all the way.
Tube should touch boom

#12 bracket

175661

Insulator

461057

1/4-20 x 3/8

#12 or #13 Bracket

1/4-20
Square

1/4-20 x 3/8

Figure 2

1/4-20 x 3/4

1/4

1/4-20

190002 installed
on all brackets
5/8 x 7-1/2 tube

175661

167-5/8”

#12 bracket

5/8 Insulator on
#13 bracket only

170410

252-1/2

#12 bracket