INSTALLATION
ANTENNA CONSIDERATIONS
Next to the trunsoeiver,the antennais the most
imporlanlcomponenr
in dsuccesslulcommunicJ-
tions station, as the communicationrangeis
directly relatedto the efficiencyol the entennc.
Thereforc,
great
careshouldbetaken
jn theinstal-
lation
of theantennasystem.
lf a proper
antennaisnot otherwise
available,
see
yolu Yaesu
dealerfor aspeciallyfactoryadjusted
YA-10single
banddipole
antenna,
YA-ll dual
band dipole antenna,or RSL scries
antenna
(for
mobileinstallations).These
antennasarecapableof
meeting
mostrcquircments.
The FT-180Arequiresr loadimpedanceof 50
ohms at the operatingiiequency. tf the load
impodanccdiffers
greatly
fromthisfigure,thefinal
amplifierprotective
circuit will causethe power
output to decrease.If this impedancecannotbe
sgcuredon all dcsiredchannelsan antennatuner
must
beemployed
inorder
toprovide
a5o-ohmload
impedance
for thetftnsmitter.
The followi g sectionwill describetwo common
types of antennaswhich satisiy the impedanoe
roqrirementol the
FT-180A.
(1) DoubletAntenna
TheDoublet,
or Dipole
antennd
consists
of ahalf-
wavelengthof wire, cut into two equal
sections
and fed at the center.At this feeding
point, an
antennabalunmaybeutilizedto prcvent
unwantcd
radiationfrom the coaxialcable.Maximum
radia-
tion exists at right anglesto the wire. Ceramic
insulators
should
beinstalled
onboth endsof the
antenna,irnda suitablecenterinsulator
mustirlso
be Lrsed.llowever,
sometypesof antenna
baluns
inclLrdemountinghooksfor thc antennaelements,
thus eliminatingthe needfor a centerinsulator.
Theseparts may be obtainedfrom your Yaesu
dealer.The correctlengthfof a doubletor dipole
antenna
can be determjnedbl, usiig oneof the
followingfonnulasl
Cut theappmpdatelength
of wirc (allowing
some
extra lengthfor fastening)
into two equal
pieces.
Tie one end of eachto a cenmic insulato.,and
connectthe otherends
to the antennabalun(or
center insulator).Connect the coaxial feedline
(typeRG8A/U
orequivalent)
to theantennabalun.
lf anantenna
balunisnot beingused,
connectthe
centerconductor
of the coaxialfeedlirre
Loonc
sideof the centerinsulator's
wire,andconnect
the
shield
of the coaxialline to the othersideof the
center
insulator
(thercis no direct connectionof
onehalf of the dipole
to the other).Thefar ends
of ihe wire elementsmay then be secured,using
nylonropetied to theinsulators.Using
supporting
poles,
hoist the dntennaashighan in the clearas
Possible.
Check
to seethat
theSWR
islessthanl:1.5 ut
the operatingfrequency.
If so, the installation
iscomplete.
Thedipole
antennaworksbestif it is
plaoed
high and in the clear,
sousethe highest
support
possible.
Whcnbuilding
the supports,
rcmembcr
that they shouldform a line perpen-
dicular
to thelinerepresenting
the
shortestdistance
to the station with which communioationis
desired.
,168
Length =
Length=
Frcq
(MHz)
t12.5 (meters)
7
Frcq
(MHz)
Doublet
Antenna
