MFJ MFJ-1890 Manuale utente

CAUTION: Read All Instructions Before Operating Equipment

300 Industrial Park Road

Starkville, MS 39759 USA

Tel: 662-323-9715 Fax: 662-323-6551

MFJ-1890

2 Element Moxon Beam for 10 meters

INSTRUCTION MANUAL

GENERAL DESCRIPTION

WARNING

WHEN INSTALLING YOUR SYSTEM, TAKE EXTREME

CARE TO AVOID ANY ACCIDENTAL CONTACT WITH

POWER LINES OR OVERHEAD OBSTRUCTIONS.

FAILURE TO EXERCISE THIS CARE COULD RESULT

IN SERIOUS OR FATAL INJURY

The Moxon Rectangle is a close-spaced 2-element Yagi consisting of a driven element

and a reflector with the element tips folded toward each other to reduce turning radius.

The Moxon features a broad cardioid pattern with roughly 3.3 dBd of foward gain and

front to back ratio measuring -30 dB or more. Spanning just over 12 feet and weighing

only a few pounds, it is well suited for rooftop installations using lightweight TV hardware.

Choosing a location

For best performance on receiving and transmitting, mount the antenna in a clear location

above or away from buildings, towers, feedlines, utility wires, and other antennas. While

your own ingenuity and particular circumstances will determine the final mounting method,

we’ll pass along a few ideas for both permanent installation and portable operation.

Never mount this antenna in a location that will permit unsuspecting people to come in

contact with the antenna elements.

Never mount this antenna where a mechanical failure might allow the antenna to contact

power lines or other utility wires.

Always ground the feedline at the point where it enters a building to a good earth ground

for lightning protection.

WARNING Always mount this antenna so that it is out of reach of adults and children.

The elements can cause injury and/or severe RF burns.

Permanent Installation

The ideal installation is a rigid pole or roof mount that puts the antenna completely

in the clear. If the ideal installation is not possible, choose the best compromise.

TV mast, heavy-duty rigid electrical conduit, and steel water pipes are suitable

mast materials. The use of soft or thin wall mast is not recommended.

Portable Operation

The MFJ-1890 may be easily transported to temporary locations for portable,

emergency, and contest operation. Even for temporary or portable operation, do not

be casual about selecting a suitable mast. If the antenna falls, it can be damaged and

may cause serious injury. Whatever type of installation you choose, remember that

the antenna should be installed where it cannot be contacted by people or animals or

come in contact with power lines.

Antenna Assembly

Assemble the antenna on a flat level surface. Avoid assembly over grass as you may

drop some of the parts and never find them again. You may use a couple of saw horses

or other means of support to aid assembly. Loosely assemble the #1 and #11 brackets

using the 1/4-20 nuts, bolts and washers as shown in figure 1. Don't forget the square

nuts that go inside the brackets. The square nuts are different for each bracket and also

take different bolts.

Figure 1

24 14

This hole should be 3 inches

from the end of the boom

Secure the driven element insulator to the other end of the boom also allowing 3 inches

from the center of the bracket to the end of the boom. Install the remaining two main

elements to the insulator as shown in figure 2. Leave the bracket loose enough to align

the elements when the antenna is finished.

Figure 2

Install the 5/8 elements into the bracket while it is loose on the boom. Tighten them

enough to hold the element but allow for the bracket to rotate on the boom as you

will have to align the elements with the mast when the antenna is fully assembled.

3/8 x 9 insulator

#4 hose clamp

Assemble the end elements as shown in figure 3.

Use the #4 hose clamps to secure the tubing

together. The corner tubes have one side longer

than the other. The short end should insert into the

7/16 x 20 elements. Repeat this assembly again

to make the other side of the antenna.

Short end

Figure 3

Short end

7/16 x .028 x 26

7/16 x .028 x 18

7/16 x .028 x 26

28-1/2”

6-1/4”

20-1/2”

Install the end pieces onto the elements using the #4 hose clamps. Sliding these end

pieces in and out will be how you adjust the final length of each element. Measure the

distance from the center of the boom to the outside of the element. This distance will

be the same for all four elements. Use the antenna diagram on the next page to verify

all your measurements. Install the u-bolt on the boom. Place the 1-1/4 end caps on

each end of the boom.

Figure 4

Figure 5

Short side on Driven element

Driven element

Reflector element

Attach the feed line to the driven element as shown in figure 5. Place the 5/8 clamps

3/4 inch away from the insulator. Use the 10-24 bolts nuts and lock washers to tighten

the clamps to the tube. Place the feed line eyelets over the remaining section of the

bolt and secure with another lock washer and nut. Secure the coax to the boom with

electrical tape or other suitable fasteners.

3/4”

6-1/4” 20-1/2”

28-1/2

74-5/8”

55-1/4”

173273 5/8 x 53-1/4 7/16 x .028 x 26

7/16 x .028 x 18

7/16 x .028 x 26 3/8 x 9”

3”

long end of corner

Figure 6

DIRECTION OF

RF ENERGY

DRIVEN ELEMENT

REFLECTOR ELEMENT

Final Assembly

Check the alignment of the elements and make sure all hardware is tight. Mount the antenna

in the final location.

Connect the coax balun to a high quality low loss cable such as LMR-400 or equivalent.

SWR Check

Resonance can be checked with an MFJ-256 or MFJ-269. Alternately a transceiver and

SWR meter can be used. Resonance may be changed by adjusting the length of the elements.

If the resonance point is too low, shorten the element length. If the resonance point

is too high, lengthen the element length.

Grounding Considerations

Although this antenna is designed to operate efficiently without the requirement of an earth

ground, safety grounding must still be provided to protect equipment, property and persons

from the hazards fo lightning strikes and other weather related electrical discharges. In addition,

the coaxial cable feeding the antenna should have the shield grounded to eliminate the risk of

any indoor equipment failure allowing hazardous voltages that could create a shock hazard.

Adequate protection can be accomplished by grounding the shield of the coax to a good earth

ground where it enters the building, or directly burying the cable in the earth for several feet

before it enters the building. For maximum lightning protection, the coaxial cable should be

totally disconnected from the station during threatening weather conditions.

PARTS LIST

173273

20-1890-1

20-1890-3

20-1890-4

20-1896-5

20-1890-6

13-1890-1

161422

165138

17-1890-1

745-3104S

461057

171329

455630

758-9199

505266

500156

554099

711-1037S

554071

551367

555362

504069

500158

562961

Tube 5/8 x 53-1/4 swaged ----------------------------------------

Tube, Boom, 1-1/4 .058 x 61-1/4” Drilled --------------------

Tube, 7/16 x .028 x 26” slotted ----------------------------------

Tube, 7/16 x .028 x 18” slotted ---------------------------------

Tube, 3/8 corner ---------------------------------------------------

Rod, Fiberglass 3/8 x 9” -------------------------------------------

Balun Assembly ------------------------------------------------------

Bracket, # 11 ---------------------------------------------------------

Bracket, # 1 ----------------------------------------------------------

Parts Pack MFJ-1890

Hose Clamp #4 ------------------------------------------------------

Insulator 1-1/4- 5/8 ------------------------------------------------

Clamp, 5/8 ------------------------------------------------------------

Caplug, 1-1/4 ABS ------------------------------------------------

U-bolt 1-3/4 ----------------------------------------------------------

Bolt, 1/4-20 x 3/4 ---------------------------------------------------

Bolt, 1/4-20 x 3/8 ---------------------------------------------------

Nut, 1/4-20 Hex -----------------------------------------------------

Washer, #10 Internal lock -----------------------------------------

Nut, 10-24 Hex ------------------------------------------------------

Nut, square 1/4-20 -------------------------------------------------

Nut, square 10-24 --------------------------------------------------

Bolt, 10-24 x 1 ------------------------------------------------------

Bolt, 10-24 x ½ -----------------------------------------------------

Washer, 1/4 Internal lock ----------------------------------------

SITESELECTION

Beforeattempting

to install

your

antenna,thinkwhere

you

can best

placeyour

antennafor safety and

performance.

To determine

a safedistancefromwires,

power

linesandtrees:

1. Measurethe heightofyourantenna.

2. Addthis

lengthto the lengthof

your

toweror mast,andthen

3. Double

thistotalfortheminimumrecommendedsafedistance.

you

areunable

to maintainthissafedistance,STOP!GETPROFES-

SIONAL

HELP.Manyantennasaresupportedby

pipe

mastsattached

to the chimney,

roofor sideof the house.Generally,the higherthe

antennais abovethe

ground,

the

betterit performs.

Good

practice

to install

your

antennaabout5 to 10 feetabove

the

rooflineand

away

from

power

linesandobstructions.RememberthatFCClimits

your

antenna

heightto 60 feet.lf possible,

finda

mounting

place

directlyabove

your

set,

where

theantenna

wire

can

takea short.verticaldroo

on theoutsideof thehouseforentry

througha

wall

orwindowneartheset.Yourdealercarries

a complete

lineof installationhardware.

AVOIOTHISLOCAnOil

safe distancefrom

The

power

linesshouldbe

at leasttwicetheheight

of the antenna

and

mastcombined.

CHOOSEA PROPER

SUPPORT

AND

MOUNTING

METHOD

However

you

decideto

mountandsupport

your

antenna

always

make

surethat

safetyis

your

firstconcern. Someofthemorecommon

installation

methodsareillustratedbelow.

RO OFMOUNTI NG

Theswivelfeatureof "universal"typemounting

brackets

makesa conve

nient

antennamountforflator peaked

roofs.Oneblamptypebracketis

usedwith3 or 4 guy

wiresequallyspacedaroundthemastandanchored

totheroofor

eavesbyeyebolts.Applyroofingcompoundaroundthebase

ofthebracket.screwsandeveboltsfor moisturesealino.

TELESCOPING

MAST

Guy

wiresshouldbe equally

spacedin at leastthreedirections.

Useat

leastthree

guy

wiresforeach

10footsectionof mast.

SI DEO F HO US E

MO UNTING

Thesafe

distancefrom

power

lines

is at leasttwicethe heig ht

of antenna

andmastcombined.

Whe reroofo verha ngis notexcessive,thesi deof

the

house

provides

a convenientmounting.

Positionthebrackets

overa stud

if possible,

one

abovetheother,andspacetwoor threefeetapart.For

metalsiding,first

markmountingholes,thendrill

pilot

holesthrough

the

sidingto

acceptmountingscrews.

TOWER

Towersafetyis

paramount

to a good

installationandrequiresthat

you

take

location,tree

growth,

soildepthand

proximity

to buildingsintoconsider-

ation.

Towerfoundationsmust

be securelybasedon a solid

concrete/

towermounting

plate.

An alt er nativ eis to si nka 4-6f ootsectionof tower

intoa concretebasefor an extremely

ruggedmount.Proper

guying

essentialto a safeweather-resistantinstallationthatmusthandlesevere

windloadingandis best

accomplishedwith

preformedguygrips,

torque

CH IMNEYMOUNT ING

Thechimney

is of te nan e asyand

conve-

nient

mounting

place.

Butthe chimney

must be strong

enoughto supportthe

antenna

in highwinds. Do not use a

chimney

thathasloosebricksor mortar.

good

chimneymount

makesuseof a 5 or

'10

foot,

1-114"diametersteel

mast,anda

heavy

dutytwostrapclamp-type

bracket.

Installtheupper

bracket

just

belowthetop

course

of bricks,and the lower

bracket

twoorthreefeet

belowthe upperbracket.

Formaximum

strength,spacethe

brack-

ets

as farapartas

possible.

brackets

andturnbuckles.Whenworkingon

towersalwaysusea safety

beltmadeof

high

quality

web-typematerial

ROOFMOUNTEO

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