Arrow Antenna.pdf

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The
Arrow
An
Hit
the
bull's-eye
with
this
pon'able
VHF
sharp
shooter.
by
Mike Walker
KA0VFF
and
Al
Lowe
NBIMW
M
ow
would
you
I i k e
a
com-
pletely
portable,
4-
element
2
meter
an.
tenna
that
fits
into
its
own
I"
x
I n
x
48"
bmm?
Not only
does
it
fit
inside
its
boom,
but
it
can
be
assem-
bled
in
approximate-
ly
two
minutes.
1'11
just
bet
you
are
quiv-
ering
with
excite-
rnenr!
Calm
down
and
reach
for
a
quiver
of
aluminum
arrows.
Aluminum
arrows
are
the
secret
to
the
versatility
a d excep-
tionak
gain character-
istics
of
the
Arrow
out
the
Peneetor
ele-
ment,
m
the
geoond
d
Photo
A.
?lie
Arrow
Anrenm.
director element
at
I
"
f m
theend
of
the
boom.
Mount
dl
ele-
men&
in
the
center
of
the
boom
w i d t h .
Place
the
driven
ele-
ment
15-5/16"
inches
from
your
first
mark,
o
16-5/16"
h m
the
r
end
of
the
born.
The
spacing
i s
slightly
less
than
0.2
wave-
lengths.
In
a
like
manner,
I
out
t k
q
pasitions
far
the
first
director.
The
driven
etement
and
the
first
director
w i l l
be
spaced
at
approxi-
mately
15-5/16"
in
the
wmer
of
the
bwm,
Now you
have
estab-
lished
all
of
y w r
element
Imations
[see
Fig-
ure
4).
At
erech
of
the
element
locatiws,
drill
a
through-hole
1
1164"
in
diameter
fora
@-32
threaded rod.
Using
the
reflector
as
the
Mferecm
for
h e
rear
of
the
antenna,
m e
up
to
the driven
elernem
4%-32
hole
lccation
and
establish
the
hole
location
for
the
P U S 9
bulkhead
connec-
tor
exactly
1
"
on
center
forward
from
h e
driven
element,
or
17-5/16"
from
the
rear
of
the
m.
bulkhead
manectar
requires
a
The
5/8#
t h ~ g h - h o l e .
You
should
ncnv
have
holesdrilled
fOr
each
ofthe
elements,
and
the
hole for
gamma
match
and
coax
co&ons
along
the
boom
(see
Figure
2).
The
desired
poiarizatlon of
your
a n t e m
will
&mine
the
[mationof
the
U-clamp.
During
our
fab-
rication
of
the
A m w
Antenna
we
placad
the
U-clamp
at
the
b a 4 m e
point
of
the
antenna.
I
you
use
the
antenna
in
the
vertical
position
f
it
is
imperative
that
the
gamma
match
be
above
the
b m
and
the
coax
run
dong
the
boom
to
the
mast.
Hf
the
coax
is
parallel, close
to
the
driven
element,
a t n
gerfomawe
ne m
Antenna.
This antenna
has
proven
to
bt
very
ver-
wile.
While hiking
in
the
Rocky
Mountain
National
Park, I
used
my
antenna
as
a
walk-
ing
stick.
Dnring
rest
stops
it
was
just a
mat-
k r
of
pouring
out
the
boom
contents,
taking
a
couple
of
minutes
for
assembly time,
and
J
was
on
the
air!
I n
rn
emergency.
this
antenna
is
ideal.
It
will
storeeasily
m
thetrunkof
your
car,
ready
for
any
situation.
Another
advan-
tage
of
the
antenna
is
that
it
is
not
prone
t
o
damage
because
its
contents
are
protected
by
the
boom.
Foxhunting
activities
can
be
stressful
to
your
antenna,
especially during h e
heat
of
the
chase. Your
Arrow
Antenna
wilt
be
able
to
withstand
lots
of
abuse,
even
when
your
partner
drives
under
low-hanging
tree
limbs.
At
every
public
service
event,
it
seems like
the
check
point
assignments
are
in
the
worst
possible locations.
The
Arrow
Antenna
will
help
you
s h m
your
way
wt
oft-
pis-
where
a
rubber
duck
and
an
HT
would
not
be
sufficient.
if
yw
need
antennagain,
portabil-
ity
,
and
a
rugged
antenna,
h n
read
on.
e
Another
unique
aspect
ofthe
Arrow
Anten-
na
is
the
gamma
match. A1
Lowe
NBIMW
is
to
be
credited
wh
the
design
of
the
gamma
i
march.
The
gamma
match
makes
the
Arrow
Antenna all
the
more
portable.
spent
sev-
long
evenings
fabricating
prototypes
of
the
gamma
match
before
finalizing
the
de-
10
73AmatWR&b
T a y
April,
1992
sign.
m e r r
you
stan
conmmiofi
ofthis
an-
tenna.
I
am
sure you
will
eppteciate
the
clev-
erness
of
Al's
design.
Comkuction
To
beginconstructionof
&Arrow
Anten-
na
you
have
the
option
of
wing
rwr
measure-
ments,
ortoamomdesign
your
antenna
fora
specifi
frequency.
Our
design
is
not
new.
It
is
basically
a
capy
o
the
srandard
NBS
(now
f
called
h e
National
Institute
of
Srandards
and
Technetogy),
with
some
variations.
Our
Ar-
row
Antenna
dimensionsare
calculated
fur
a
center
Frequency
of
146.520MH~
k
fairly
It
broad-banded,
having
k n
tunad
lout
of
band
for
use
in
areasearchand
rescue
mrnunica-
tion
a m d
143
MHz
and
149
MHz.
The
materials
for
the
antenna
ate
readily
available.
If
you
ate
handy
with
a
drill press
and
a
hacksaw,
yoti
will
have
no
problem
hading
and
assembling this
antenna.
Stethe
Parts List
for the
materials
needed.
Using
a
drill
pws
for
mstruction
of this
antenna
wBI
enhance
the
overall performance
of
your
antenna.
The
mechanical
integrity
of
ywr
antenna
will
be
a
natural
progression
betauserha
drill
press
wj1I
inherently
keepall
your
elements
parallel
and
perpendicular.
For
our
purposes,
antenna
performance
dictated the
selectionof
a
48
"
boom.
Meamr-
iag
from
each
e d
of
the
b m
material,
lay
will suffer.
Each
of
the
fallowing
m u r e m ~ ~
will
ts
be
used
to
establish
clement
lengths.
Using
a
tubing
cutter,
scribe
the
outside
of
each
ele-
ment
a
the
desired
length. Grasping
the
ele-
t
ment
on
either
side
of
the
scribe
mark,
you
~
""',
?
~
~PLASTIC
TIP
\ARROW
SHAFT
GLUE.GROOVES
,~
I..
lfu
ELEMENT LENGTH
..\
\
.
8-32 THREADED
INSERtj
Figure
1.
The aluminum arrow element.
8- 32 STUD
:::::::.::}.u
800M
BARREL CONNECTOR
--------
--------
PANEL
NUT
-~
Figure
2.
Attaching the elements to the boom. The feedpoint connection is also shown.
r6"
u=(
SOLID BRASS ROD
6 IIBRASS TUBE----.
J
~
7 1/2" PLA;T~C-TUB~3
~
insert. Our prototype antennas both used
larger diameter arrows. The change to the
1816 was only a factor of cost.
Starting with the
19-7/8"
reflector pairs,
install one 8-32{threaded roo I" into one of
the element halves. In our construction, we
used LOC-TITE'" to permanently affix the
8-32 x 3" roo into the arrow shaft. Install the
remaining threaded roos into the other three
element halves.
To fabricate the gamma match you will
need a PL259 solderless connector, a 6" solid
brass roo 0.080" O.D., a brass tube 0:180"
I.D. x 0.240" O.D., and a plastic tube 0.175
O.D. x 0.080 I.D. 7-1.2". Solder the 6': brass
roo into the center of the PL259, flush with
the tip of the connector, just as you would for
attaching RG-58 coax. Next, slide the 7-112"
plastic tubing onto the 6" brass rod and cover
,the plastic tubing with the 0.180" I.D. x
0.240" O.D. brass tube. This assembly is
now your gamma match. To complete the
assembly you will need to epoxy the plastic
tube into the connector. After tuning the an-
tenna, you may want to tape the brass tube in
position, and mark the position of the short-
ing bar for convenient setup in the future.
To make the shorting bar for the gamma
match you wilkneed a small piece of alu-
minum 1.5" x 0.5:' x OS' (see Figure 5).
Measure and mark a place on the aluminuJ11
block
l/4"
from on~ end and
1/4"
from the
edge of the block. This should place your
mark along the center of the width of the
block. Measure exactly}" from the previous
mark and again center this mark along the
width of the block. Drill a hole
7/32"
through
at your first mark and drill a through hole
9/32"
at the second mark. Standing the block
on end, drill a 0.201" hole into the 0.5" x
0.5" block end, keeping the hole centered in
relation to the block. DriJIinto each end of the
block until the drill bit is visible through the
previously-drilled
7/32"
and
9/32"
holes.
Tap the two end holes for a 1/4"-20 thread.
Two
1/4"-20
bolts will be used for setscrews
to attach the shorting bar between the gamma
match and the driven element.
Assembly
.
~
6~
I
LpL259
. RADIO SHACK #278-196
Figure
3.
Preparing the gamma match.
will be able to precisely snapthe element into
two pieces, using the following element
lengths: Scribe two arrows at
19-7/8",
two at
19-1/4",
two at
18-1/4",
and two at 17-118".
These pairs of elements will make up the
reflector, the driven element, and the first
and second directors, respectively.
The Easton EAGLE 1816'" arrow shafts
that I used have conical plastic tips that are
used for cementing on the nocks in normal
arrow construction. The plastictip should
not
be used when measuring the element length,
but should be left intact in order to seal up the
end of the element. When you purchase the
arrow shafts from an archery supply store,
12 73Amateur
RadioToday
"April. 1992
you will be given inserts that are used for
attaching the field points to the arrow shaft.
These inserts will be used for attaching the
elements together and to the boom. When
installing the inserts, apply a small amount of
epox1.
Please note that tI1eboom width is not in-
cluded as part of the calculation for overall
element length. The element diameter will
have an effect on element length, and I do not
recommend exceeding the element diameters
by more than 0.100". Many aluminum ar-
rows are greater 'in diameter than the 1816.
Easton EAGLE. The 1816 is the smallest
arrow shaft that will accept the 8-32threaded
The Arrow Antenna is now ready for as-
sembly. Place the threaded end through the
lI/64" hole in the boom and scr«w on the
other half of the element. (See Figure 4 for
the correct placement of the elements). Con-
tinue down the boom, installing the ,restof the
elements. Screw the bulkhead connector onto
the gamma match, then screw one of the
panel nuts flush to the gamma match. Now
insert this assembly through the
5/8"
hole
forward of the driven element, tightening it in
place with the bulkhead panel nut. Attach the
shorting bar over the end of the driven ele-
ment that is parallel to the gamma match.
Slide 'the bar along the element until you
reach the end of the gamma match, and slide
the shorting bar onto the end of the gamma
match. Using the 1" x
1/4-20
bolts, fasten the
shorting bar so that it is flush with the end of
the gamma match. Connect the coax to the
other end of the bulkhead connector. Mast-
mount your antenna and route your coax so
SmRTlNG
B P I
a
u
SOLOERLESS
PL259
GAMMA
MATCH
SHORTING BAR
BULKHEAD
COMNECWR
that
it
is
clwc
tto
the
h w q
and
mast.
You
arc
~
now
ready
to test
and
tun&
your
antenna.
Testing
and Tuning
The
antenna
is
tuned
by
sliding
the
nutcr
brash
tubc
out
and
moving
the
shorting
bar
along
the
gumma
match
asscmbly
and
test
for
thc
bcst
SWR.
In
our
cxpcricncc,
the
antcnna
?rhnuld
Rewithinxceptabtclimibof
<
1.3:l,
if
rhc
assembly
has
h e n
constructed
careful-
ly.
Our
untcnnas
havc
all
tun&
toan
SWR
of
I.
1
:
1
at
146.520
MHz.
Disasscmblc
the
antcnm
and
scrcw
t k
cle-
ment
pairs
kogcthcr.
Install
one
of
the
t
-
114"
rwtch
tips
onto
om:
end
o
thc
boom.
Insest
C
thc
bundlc
of
the
fnur
clement
pairs
inlo
the
horn.
Drop in
thc
gamma
match
and
short-
ing
h r .
Install
the
sccond
crutch
tip,
and
you're
w d y
to
go
pnrtable.
NOTE: For
pcmanent
installation.
I
KT-
ommcnd
that
star
w~shenr
installed
when
be
artaching
thc
ctcrnenu
to
thc
h m .
The
addi-
~ i ~ u r
77ze
4.
e
overnil
dimetwions
o
the
campie~ed
f
Armw
Anrenm.
I
The
A
S&f@aIiins
tion
oI'
star w~slicrs
should
keep
the
elmenh
hvlm
viblzlting
loosc.
Nomal.care
shouid
be
takm
to
weathcrpmf
yolrrantcnna.
Seal
the
CW~X
cnnncctirm
and
!he
end
of
the
gamma
match
assembly.
We
Won
a
Resptable
Second
P k e
I
cntercd
thc
anrenna
in
the
1941
Dayton
Warnvcntion
YHF
antenna
cumpetition.
A l
NOIMW
and
I
h t h
wnndcrad
how
the
k m w
Antcnnu
wnuld
mcasurc
up.
W e
were
not
dixappointcd
with
thc
rcsul~s;
in
thc
homc-
brew
category,
the
antenna
mcasurod
6.1
dB
gain
over the
refcrcnce
dipole
used
far
test-
4'Elemertt Material
?075
alurnlnum
(Arrow
Shatts)
Gain
Measured
( h a r d )
&
over
reference
d i m
dB
I
(estimated
ever
9dBij
Measured
{front-bback]
10.1
dB
Note
tor
direction
finding:
This
makes
the
glsnal
peakdlrectly
u f f i h e ~ ~ f
dampest
h e
RulldiradlymhbBcRoitkEBntenna.
Special
Fearwes
Pmtabte
Allantenna
hardwrrre
fltstnside
me
Ixx#n
far
storage
or
t r a m
AssemMy
lime
h s s
than
two
minutes
2402.
We$M
Ba~4wldth
4h!kiz(144-148)
SWRwer
Madwidth
<1.5:1
SWR
at
T 4 6 . 5 2
<1.1:1
il.
PartsL#sl
1
"
x
1
"
x
48"
piecaaf
square
aluminumtubing
(MOTE:
T h e w e l t t h i e k m k w r
squmtubing
waab.0825"
allowing
us
to
pack
all
the
antenna
bdwarethsida
the
boom.)
Aluminumorruws
2 0
In
length.
and
appmximately
W
in
diamstef
2"
2"
PLZSB
bulk
head
c ~ n a c t o
d en t
r
w l us
SoMiessPt.259
RadbShack
#27&
1
W
h i eP
L
m
i
-
~
mnetler
~acl~o
shack
83
8"
x
0 . W diameter
b p C s 6
T-1STx
0
:
-
bDTx
RTTS"O.D:pTaStJctube
6
r B . $ W
r0.2WO.D;
1-118"
diwRetw&bPcrUtGk#lp
-
W 2
x
2-1
12"
pieces
of
threaded
rod
Conllguration
Number of
elements
Matching
System
Baom
Diameter
Boom Length
m
Antenna
Ya@
4
,a
h
.a5
Gamma
1
"
square, alumlnum
/.
ing.
Thc
winning
antenna
was
35'
long
with
I9
elcmcnts
and
14.3
dB
gain
over
the
rcfcrence
dipale.
,Al
and
I
will
be
looking
forward
to
Dayton
'92.
Wc
will
bc
rcady
to
compete
agaln.
I
was
fonunatc
to
have
John
W d
KC0WA
as
my
rncntW
for
antenna
construction.
Bccause
of
John's
cncoutagerncnt
and
hdp during
nut
an'tcnna
expcrimcntation,
thc
Armw
Antenna cvtllvcd
to
its
present
form.
Yell
mav
rvJntacT
Mike
Walk@
U V F
@ F
at
3816Ash
A
wnue,
Lor.dund
CO
80538.
m
,
~~
14-O
x
1"
b l t 3
1'S
0.5"
x
0.5*
x
1.5"
aluminurnbar

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