Cushcraft DB-46M8EL User guide

Cushcraft

Amateur Radio Antennas

DB-46M8EL

Dual band 6 and 4 Meter, 8 Element

Beam Antenna

INSTRUCTION MANUAL

VERSION 1B

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 DB-46M8EL is a dual band 50, 70 Mhz 8 element beam antenna . It uses a single feed point
for both bands eliminating the need for a splitter or duplexer. the open sleeve method of providing dual
band performance is very efficient. there are no traps or coils inducing unwanted loss and there are no
compromise spacing of elements with this antenna either. Each band has a set of full-length elements
which have had both length and position on the boom computer optimized using the latest in Partical
Swarm Optimisation techniques (PSO) ensuring the best possible performance. This antenna provides
both a 4 element Yagi on 50 Mhz and a 4 element Yagi on 70 Mhz although only the 50 Mhz element
is fed. All of the 70Mhz elements are parasitic.

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

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)

555747
564792

562961
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)

and the 5/16 split washers (564792).

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.

385144-1

540067

385142-1

Short tube ( 34 inch )

Long tube ( 56 inch )

Front of antenna

3

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. Notice
there are two different locking bolts for the brackets.
The driven element bracket (#1) uses a larger 1/4-20
bolt and square nut.

2 inches

12-1/2 inches

36-1/4 inches

39-1/2 inches

#1 Bracket

44-3/4 inches

461057
Insulator

47-1/2 inches

#11 [10-24 x ½]
#1 [1/4-20 x 3/8]

#11 or #1 Bracket

#1 [ 1/4-20 ]
#11 [ 10-24 ]
Square

1/4-20 x 3/8

1/4-20 x 3/4

1/4

1/4-20

Figure 2

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.

5/8 Insulator on
#1 bracket only

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

4

80 inches

Front of antenna

84-1/2 inches

Install boom caps

Figure 3

Instal the tubing in the locations shown.
The tubing can be identified by the lengths
given on the right 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.
Slide a #4 hose over each element.
Verify the measurements and tighten the
clamps on each element as you set it.
Install the 7/16 tube caps on the ends of
the elements when finished. Stand back
from the antenna and check the alignment
of each of the brackets. Level them if needed
and tighten the locking bolts on top and bottom
of each bracket.

63-7/8 inches

Identify each element by

its tube length

171533 tube 58 inches

43 inches

Measurements are from center

of boom to tip of element.

62-3/8 inches

42 inches

57-1/8 inches

41-3/4 inches

39-5/8 inches

55-1/4 inches

171500 tube 38 inches

171533 tube 58 inches

171153 tube 37 inches

172928 tube 53 inches

171153 tube 37 inches

Front of antenna

176212 tube 34-1/2 inches

172928 tube 53 inches

Figure 3

5

5-3/4”

FEED LINE CONNECTION

Center
Conductor

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.

11

To RF Choke

Coax Stripping

10-24 nut

Element

10-24X1

5”

50 MHZ Driven Element

70 MHZ Driven Element

#10 lockwasher

3/4

Shield

1

Front of antenna

171329

It’s okay to spread the clamp
to install onto the 5/8 tube.

Tape

RF Choke: 12 turns of
RG-8/U with a six inch
diameter.

Tape

6

FINAL TUNING

Tuning of the antenna is done by moving the driven element (#1 Bracket with insulator) in or
out. Both sides of the driven element must remain the same. If you move one side, you must
move the other the same distance. 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

50 MHZ Driven Element

70 MHZ Driven Element

Front of antenna

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 and 70.000
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 elements should be slid 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 in frequency as you shorten the driven element. Continue
this adjustment until the frequency you desire has the lowest SWR. If the frequency is too
high then lengthen the driven element to lower the frequency. It is not necessary to tighten
the element clamps completely each time you adjust the distance. The tubes should have
enough friction to remain where they are if you just snug the clamps. The hose clamps can
be over torqed and damaged. Repeated over tightening can wear the clamp and it may need
replacing. When your happy with where the antenna is tuned, then tighten the clamps.
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

NOTES

8910

PARTS LIST

PN DESC QTY
174939 7/16 tube 4
176212 7/16 tube 2
171153 7/16 tube 4
171533 7/16 tube 4
171500 7/16 tube 2
505266 1/4-20 X 3/4 BOLT 68
554099 1/4-20 NUT HEX 68
555693 10-24 NUT SQUARE 14
500158 10-24 X 1/2 BOLT 14
562961 1/4 LOCK WASHER 68
161422 #11 bracket 14
165138 #1 bracket 2
171329 5/8 CLAMP 2
170256 1-1/4 X .035 X 57 1
170234 1-1/4 X .035 X 32 1
455630 1-1/4 TUBE CAP 2
475639 7/16 tube cap 16
190002 5/8 x 7.5 tube 16
461057 5/8 insulator 2
504069 10-24 x 1 bolt 2
554071 10-24 nut 4

711-1037S #10 lockwasher 2
745-3104S #4 hose clamp 16

385142-1 boom to mast 1
385144-1 backup plate 1

540067 u-bolt 2
564792 5/16 split washer 4
555747 5/16 hex nut 4
500156 1/4-20 x 3/8 2
551367 1/4-20 square nut 2

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