CUSHCRAFT LFA-6M4EL User manual

CAUTION: Read All Instructions Before Operating Equipment
308 Industrial Park Road
Starkville, MS 39759 USA
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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
2

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
3

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
#11 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
4
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
5
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
1
#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
Tape
It’s okay to spread the clamp
to install onto the 5/8 tube.
6
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.
7
Mast
Mast

NOTES
8

9

10