MULTI BAND HF FAN DIPOLE ANTENNA DESIGN.pdf

MULTI BAND HF FAN DIPOLE ANTENNA DESIGN

http://www.hamuniverse.com/multidipole.html

BUILD THIS MULTIBAND FAN DIPOLE

FOR ALL BAND HF ANTENNA EXCITEMENT

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CONSTRUCTION UPDATES FOR EASIER TUNING - 9-08:

Based on research done by the Stanford Research Institute

(SRI) to construct a three-frequency multi-band dipole that

would work without any need for cut and try techniques, we pass

on this information in the hope that it will help you more easily

get this type of antenna on the air quicker.

What they came up with was much improved method over

the old cut and prune technique.

They found that the wires at the center feed point had to be

separated by at least 5 1/2 inches vertically and the ends

separated by 38 inches in the 2 to 18 MHz range.

By this simple change they found that you could accurately cut

the antenna element lengths for given frequencies and eliminate

the need for pruning.

In the drawing above , the lowest frequency antenna is on top

and is cut 4% short of the standard 1/2 wave length. (Length in

feet= 0.96 times 468 divided by the operating frequency in

MHz).

The middle frequency antenna (lower in frequency), is cut for an

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22-07-09 11:54

MULTI BAND HF FAN DIPOLE ANTENNA DESIGN

http://www.hamuniverse.com/multidipole.html

exact 1/2 wave length. (length in feet= 468 divided by the

frequency in MHz)

The highest frequency antenna is at the bottom and cut for 1%

longer than the 1/2 wavelength (length in feet= 1.01 times 468

divided by the frequency in MHz)

The only construction effort necessary over a standard

multi-band dipole is the fabrication of a feed block or center

insulator that is about 12 inches vertically by 3 inches wide ,

made of a good insulating material, such as Lucite, Bakelite,

fiberglass, or PVC.

The end 38 inches of separation can be maintained by separate

halyards on each element or a spreader bar with a common

halyard.

The bandwidth will be at least plus or minus 2% for a 1.5 to 1

SWR according to Stanford Research Institute.

Editors note: It is assumed that this method will only work

as described, if you are working with a "3 band" multiband

dipole. We do not have information for use with over 3

bands. If you arrive at a better method, let us know!

You can chose whichever method of constructing the

multiband dipole using either the method above or use the

old cut and try method below......your choice.

We would appreciate any feedback if you use the newer

method ABOVE!

Email n4ujw at hamuniverse.com with your comments

See how others have built it using the new

method!

http://www.sstowers.com/aa4cv

Cool fan dipole project using the " Ugly Balun "!

Older cut and try method below:

2 z 6

22-07-09 11:54

MULTI BAND HF FAN DIPOLE ANTENNA DESIGN

http://www.hamuniverse.com/multidipole.html

CONSTRUCTING THE MULTIBAND DIPOLE: (Older cut

and try method)

Here is a fairly simple and easy to build multi band horizontal fan

type dipole that can be constructed for all band operation from

160 meters up thru 6 meters or even higher.

In the drawing above, it is shown for just four bands, 80 thru 10.

One separate dipole for each band needed. However you can

build it to suit your own preferences by using the standard

formula for a dipole:

468/freq mhz = total length for each band. Use the formula for

your desired center frequency.

Each dipole length above in RED is in feet and tenths of a foot

for the center of the General portion of each band and is derived

from the above formula and should be cut longer for swr

trimming. USE #12 TO #14 GAUGE COPPERWELD WIRE IF

POSSIBLE or use what you have on hand. The top most dipole

must support the entire weight of the antenna.

Start with your lowest (in frequency) band of operation as the

main (top) support for the entire setup. Cut it per the formula but

add a couple of feet on each end for tuning. Try to use a wire

size that will support the other dipoles.

This is the main support for all the other dipoles and must carry

their weight.

Cut a dipole for each band of operation. (SEE EDITORS NOTE

AT BOTTOM OF ARTICLE )

Cut each full length in half....example: for the 10 meter length

from the formula you get 16.1 feet for the total length. Cut it in

half at about 8 feet per side. Make sure you cut each length

about a foot or more longer for swr trimming and attaching to

center and end insulators!

If you are building the four band dipole above, you should have

8 lengths of wire scattered all over your work area.

WARNING! DON'T DO IT IN YOUR LIVING ROOM, THE XYL

WILL NOT BE VERY HAPPY WITH YOU AND AFTER SHE

GETS FINISHED WITH THE QRM,,,, ALL YOUR ANTENNA

BUILDING WILL HAVE TO BE DONE FROM THE DOG'S HAM

SHACK!

It is assumed that you have your end support poles, trees,

center and end insulators, pulleys all ready to go before you

start working on the actual dipoles.

A very important part of this design is the installation of the

pulleys (in yellow on drawing) on each end attached to each side

support.

They are added to this design due to the swr trimming process

and make it very easy to pull the entire antenna up and down

while making the swr adjustments. Mount a suitable size pulley

on each end attached to your pole, trees, etc for the diameter of

cord or rope used to support the system.

Start your antenna trimming with the top dipole.... attach your

coax to the center insulator leaving several inches of the center

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22-07-09 11:54

MULTI BAND HF FAN DIPOLE ANTENNA DESIGN

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conductor and shield exposed. Each half of each dipole will be

connected to the coax center pigtail and the shield separately. In

other words, connect one side of the dipole to the center

conductor and the other side to the shield.

Attach the other end of each half of the longest wire to the

support cord and run thru the pulley on each end and pull the

dipole up into the air between the end supports. Check swr.

Trim as needed with low power for lowest swr possible, lower

with pulleys, attach the next highest band dipole electrically to

the same point as the first dipole, raise it to operating height,

check swr, lower for trimming, up and down, up and

down.........due the same for all other dipoles for each higher

band of operation.

When you are finished with the highest band of operation, pull

the entire system up with the pulleys and tie of at the bottom

securely.

Make certain that the coax center conductor is attached to one

half of each dipole and the shield to the other half. All dipole

ends at center insulator are connected together.

This may not be very clear to the new antenna builder so please

see the drawing below for the center insulator arrangement.

(NOTE: IF USING THE NEWER CONSTRUCTION METHOD MENTIONED ABOVE,

INSURE PROPER SPACING OF ANTENNA LEGS AT THIS CENTER INSULATOR!)

The white areas in the center support drawing above are

mechanical supports, clamps, wire ties or whatever your genius

can come up with to support the main (top wire) and the weight

of the coax.

Remember, all the weight of this antenna system is supported

by the top wire.

The connections should be soldered and all should be sealed

including coax end from water, ice, snow etc.

Use a 1:1 balun like the " Ugly Balun " project page on this site

close to the center before coax goes to your rig.

For best performance get it as high as possible and remember

that since this is a dipole arrangement, it will be somewhat

bi-directional towards and away from you as viewed in the

drawing. (BROADSIDE)

Remember that all elements will interact with each other in the

tuning process and the final setup must be secured so the angle

or distance between each dipole does not change when blowing

in the wind, etc.

The angle or distance between each dipole is not critical but the

final spacing must be maintained!

It will take lots of work (trial and error) in getting each dipole to

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22-07-09 11:54

MULTI BAND HF FAN DIPOLE ANTENNA DESIGN

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the lowest SWR. Just keep TRYING.

It should also be noted that the antenna can be used in an

inverted v fashion but remember the spacing should be secure

in the final operating position. Tune it as in all the above

instructions. You may use a tuner with this antenna un-trimmed

to save a lot of work!

EXPERIMENT! EXPERIMENT! EXPERIMENT!

Editors note:

The multiband fan dipole can be very difficult to tune for lowest

swr in some installations. There are many variables that will

make tuning difficult. Height above ground, sometimes the angle

of each dipole relative to the other dipoles, surroundings , etc. If

you can get the swr to around 2 to 1 or lower for each

band....don't worry too much about it. (see the newer

construction method above)

You might also consider using a good antenna tuner if you are

having major tuning problems. A 2:1 SWR or lower can be

handled by most builtin tuners in radios.

You might also consider removing HF combinations such as

40/15 meters and 80/30 meters.

For these cases, cut the element for the lower frequency and let

it serve double duty at the odd harmonic . In other words, cut the

40 meter element and let it serve also as the 15 meter element

which eliminates the 15 meter section.

Make sure that the distance between all dipole elements does

not change when tuning.

They must be in a fixed position always with some sort of

spacer. In theory, we could fashion a four-wire antenna for the

80, 40, 30, 20, 15 and 10-meter bands.

In practice, it may be difficult to obtain a good match on all

bands.

Since the resonant length of a given element in the presence of

the others is not the same as a dipole by itself, tuning can be a

tedious and difficult procedure. Adjust elements for resonance in

order from lowest frequency to the highest such as in an 80 40

20 10 combo.....start with 80 first.....then go to next higher

frequency dipole.

Always cut each dipole a lot longer than required for each band

to make tuning easier.

Trim as needed for your operating frequency.

All of these bandwidth, adjustment and matching problems are

easily solved with an antenna tuner at the transmitter, feeding

the antenna through 100 feet or less of RG-8 coax.

Please remember to send us feedback if you are using the

newer construction method or if you have any tips you would like

to pass along to others that make the multiband dipole easier or

faster to get set up! 73!

BACK TO ANTENNA LAB

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22-07-09 11:54

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