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Mobile
Antennas
There are
many
possible
mounting
locations
on a car.
Three
of
the
most
popular
locations
for
monitor
antennas are shown
below.
ROOF
MOUNT
-
The
antenna
is
mounted
in the center
of
the
roof
.
This
position
is
considered the best
by
many,
because
it
generally
results in
better
reception than
the
other
locations.
Radio
Shack's
Hi-VHF/UHF
Mobile
Mount
(Catalog
Number)
20-177 comes
complete,
like
all
our
monitor
antennas,
with
low-loss coax cable.
COWL
MOUNT
-If
you
would
rather
not
cut
a hole in
the
center
of
your
vehicle's
roof,
you
may
prefer
this
location
.
Ask
about
our
20-016
Cowl
Mount
antenna
which
is
especially designed
for
Hi-Low
VHF
monitoring.
For
UHF,
use
20-183.
REAR
DECK-Installation
in
this
location,
may
result in l
ess
noise
because
it
is
further
from
the
engine.
Your
Radio Shack salesman
will
help
you
select
the
antenna
which
is
best
for
you.
Keep
the
following
points
in
mind
when
installing
your
mobile
antenna.
1.
Mount
the
antenna
as
high
as
possible.
2.
Mount
it
rigidly,
so
it
will
remain vertical
while
in
motion.
3.
Mount
as
far
as
possible
from
the
engine
compartment.
-7-
MOBILE NOISE SUPPRESSION
This
receiver
is
ve
ry
sens1t1ve,
and
will
pick
up
signals
that
are
extremely
weak.
With
th
is
extreme
sensitivity,
you
will
fi
nd
that
the
receiver
wi
II
amplify
weak signals, along
with
any
noise
that
may
be
present.
When
operating
a receiver in a vehicle,
you
will
find
that
the
vehicle
generates noise, and
this
noise can become very
objectionable.
Mobile
operation
will
not
be
as
quiet
as
base
station
operation,
but
steps can
be
taken
that
wi
II
gr
eatly
improve
the
noise
situation.
ELECTRICAL SYSTEM:
Generally
speaking, noise can be generated
by
any
device
or
connec-
tion
that
carries electrical
current.
Any
device
that
generates a spark
should also
be
suspected. Bypass
any
suspected w
ir
e
to
ground
with
a
high
quality
1
µF
coaxial
capacitor
.
A very
common
source
of
noise
is
the
generator
or
alternator
.
This
type
of
noise
will
sound
like
a musical
whine,
and
will
also vary
with
speed
of
the engine. Gener
ator
and
alternator
noise can usually be
reduced
by
connecting
a coaxia l
-type
capacitor
from
the
armature
terminal
to
the
metal
case
.
IGNITION SYSTEM:
The
ignition
system
is
the
most
common
source
of
noise.
This
noise
can
be
identified
by
the
fact
that
its speed varies
with
the
engine
speed.
Ignition
noise
will
sound
like
a series
of
"popping
" sounds,
while
the
engine
is
idlin
g,
and
will
speed
up
to
a buzzing sound
as
engine speed is increased.
There are a
number
of
things
that
can
be
done
for
this
type
of
no
ise
.
1.
Use
radio suppression-type
ignition
wire
and resistor spark plugs.
2.
Check high-voltage
wiring
for
leakage, cracks,
etc
. Replace
any
old
wir
ing.
3.
In
extreme
cases,
obtain
an
ignition
noise suppression
kit-it
should shield all
ignition
wiring.
This
will
provide
maximum
noise
suppression.