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: 662-323-9538 Fax: 662-323-6551
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
Instal the elements 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.
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.
59-3/4 INCHES
172928 7/16 x 53 inches
Don’t tighten loop clamps
until final tuning is done
175512-1 7/16 x 42-3/4 inches
Loop End
48-3/4 INCHES
174869
175512-1 7/16 x 42-3/4 inches
174865 7/16 x 48 inches
#4 hose clamp
172922 7/16 x 47 inches
55-1/4 INCHES
53-3/8 INCHES
172922 7/16 x 47 inches
51 INCHES
FEED LINE CONNECTION
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
Center
Conductor
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.
13
Shield
171329
10-24X1
#10 lockwasher
10-24 nut
Element
Tape
Tape
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
SAME
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
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.
NOTES
PARTS LIST
172928 7/16 tube 2
175512-1 7/16 tube w/slot 4
174865 7/16 tube 2
172922 7/16 tube 4
102734 mast brick 2
172732 mast clamp 1
172735 mast plate 1
455625 2" CAP 2
505266 1/4-20 X 3/4 BOLT 53
554099 1/4-20 NUT HEX 55
551367 1/4-20 NUT SQUARE 12
500156 1/4-20 X 3/8 BOLT 12
562961 1/4 LOCK WASHER 55
500392 5/16-18X3 2
564792 SPLIT WASHER 5/16 9
5142400 5/16-18X4 1
171329 5/8 CLAMP 2
165919 #13 bracket 2
161409 #12 bracket 10
170410 boom tube 2
175661 boom tube 2
175667 boom insert 1
475639 7/16 tube cap 8
174869 6 mtr loop end 2
190002 5/8 x 7.5 tube 12
461057 5/8 insulator 2
504069 10-24 x 1 bolt 2
554071 10-24 nut 4
500349 5/16-18X5 4
506968 5/16-18X 2-3/4 2
555747 5/16 NUT 9
565697 #10 lockwasher 2
505734 1/4-20 x 2-1/2 bolt 2
745-3104S #4 hose clamp 16
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