Gift to

32 ' I "
3 2 '"
3 2 ' . "
3 2 ' I "
Fig. 8. Close-up of coaxial 'T' int erconnections. Actual
coax length from this point to the dipoles is 32 feet each
way. This section is ele vated to a height mid-point between
the heights of the two dipole centers.
DI R E CTION 0 '­
M 4 X IM U ,,", R,-
\ "
~:7"'--+-+' I --"'---i.;=:;;;- 1
u'
+,
Fig. 9. W9 HBF installation, fooking sou th. (In reality,
trees, no t poles, are used as supports.) Note that maximum
ri di rection is almost opposite to tha t of the live
d ip o le elem ents.
viewed from the top look ­
in g dow n tow a rd th e
g ro u nd . Eq u al 3 2-f o o t
lengths of RC-58 are used
between the two dipo lety
pe elements. This len gth
was chosen not scienti fica l­
ly, but simply becau se it
was the length req uired to
reach between the tw o antennas
whe n th ey we re
or iginally space d when the
array was cut for 75 meters.
But many exper ts te ll me
that this coax spacing may
have a great deal to do with
why this antenna performs
so well. I leave it up to you
to decide what will wo rk
best overa ll.
The 1 3 'h -foot offset
dipole centers also may
help to explain a great
num ber of things about this
ante nna, but I'm not sure
just what at th is po int. I
rathe r sus pe ct t hat you
could experiment with this
186 73 Magazine . October, 1980
shift co nsiderably with interesting
results.
O verall , 200 fee t of
RC-58 runs ba ck to t he
operati ng po sition from the
ante nna. I ofte n drive this
with 2 kW in, and have yet
to have a pro blem . The majority
of the coax feeds
ba ck to the ho use at the
elevated point where the
tw o coax dipole feeds
break off-so it is a lso
possi ble that the effect of
the coax adds som ething to
the ante nna itself. The coax
runs t hro ug h high t ree
bran che s m uc h as t he
eleme nts do ,
Fig. 8 shows how the
co axia l "T" is interconnected.
I simply used black
plastic elect rical tape; the
connections at W 9H SF are
not even so ldered toget
her- just twisted. You
may wa nt to experiment by
reversing the cente r con-
du ctor feeds to t he d ipo le
elements, just to see th e effect
it might have on your
pattern. I use a string to
hoist up the "T" point into a
t re e so t hat t he co ax
doesn't droop do wn into a
p la y a rea w he re t he
yo u ngs ters ofte n congregate
.
Fig. 9 shows th e installation
from t he north, looking
sout h. (poles, not trees, are
shown here to simplify the
d iag ram.) No te th at th e
area of maximum radi ation
(gain) is quite opposite to
where the cente r cond uctors
of t he coax feed . I have
no w ay to expla in this
phenomenon.
CuttinglPrun ing
I had to do no cutting/pruning
whatever. The
original 40-mete r cut, to
7.250 MHz, is the o nly cut
made, and that was by way
o f sta nda rd d ipo le fo r­
mulae.
At W9HBF, du e to exte n­
sive antenna experimentation
conducted with wire
arrays , all fee d lines go into
a switchbox and then into a
DenT ron Monito r Tuner. As
a resu lt, I've not had to be
concerned over vswr problems,
nor have I eve r had
any with this antenn a.
I can report, however,
that th is ante nna mat ches
very closel y to the settings
u sed fo r t he d oubleex
te nded zepp. In fa ct.
t he re is o nly 1 .3:1 di f­
ference between the two .
(In other wo rds , if t he
transmatch is set for the
ze pp, whic h uses a bala
nced 30 0-0 h m l ine ,
switc hing in t he unbalanced
coax feed of the array
throu gh t he OenTron
" coax"I"ba lanced" pa ne l
sw itch prod uce s only a
1.3:1 swr on the array. As a
result, only a very minor adjust
me nt is required to
bring the a rray to a pe rfec t
1:1.) This is qui te advantageous,
since it simplifies
the pr o blem of gett ing
qu ick comparative antenna
checks over the air.
TVI is one fina l aspect of
this ante nna that is worth
mentioning. No TV! can be
noted at a ll. This is not the
case w it h t he do uble ­
exte nded ze pp or th e roofmounted
ground plane .
This Array on Othe r Bands
Results on other ba nds
are interestin g. However,
my comparison standard is
a ve rtica l Hv-Cain 14AVQ
o nly. However, here's what
I get:
.20 me ters: The vertica l is
better, by 6 dB.
.15 meters: The array is
better, by 12 dB.
.10 meters: The array is
better, by 24 dB.
Need less to say, this array
sees a lot of 10-meter
use at W9HI3F . Contacts into
Europe and Asia are
es pecially good, and my
signal freq ue ntly beat s ou t
a ll t he boys with big bea ms,
as the OXstation invariably
comes back to me first. Furt
her, OX sta tion co nta cts
te nd to be so lid and reliable
(no Q5Bl, so half -ho ur-lon g
rag chews on 10 meters with
Europe are not uncommon.
Since my vertical does
not functio n be lo w 40
meters, I cannot use it as a
comparison standard fo r 75
meters. But the doubleexte
nded ze pp does wo rk
well there. A comparison
he re shows .that the zepp
has it over this array by
18 dB. This is prob ab ly
because the zepp a pproxim
a te s a d ipo le a t 75
meters. However, the array
does functi on on 75, which
surprised me.
Ov erall, though, the array
seems to shine best on
10,1 5, and 40. But because
of the lack of effec tive
ga in-ante nna compe titio n
at 7 MHz, it stands out
more on th is band than
perhaps anyw here else.
I hope that others may
experience equally satisfying
results and thafthey will
report refinem ent s that further
improve effectiveness.•