Tune-up
I n most mobile
installations,
ignition
noise is a problem.
Before
beginning
any special
noise suppression
steps, be sure that
the
vehicle
is well-tuned.
Clean
and
tighten
all
electrical
connections,
including
alternator,
battery,
regulator
and coil connections.
Perform
the
following
maintenance
steps as necessary.
Solder
any
crimped
spark
plug
or
distributor
leads;
clean
and
regap
or
replace
spark
plugs
and
ignition
points;
and
check
and
clean
alternator
rings
or
generator
brushes.
Retune
the
engine
at the
manufacturer's
recom-
mended
intervals.
Corrective
Steps
Usually
several
sources of
noise are present
in any vehicle,
with
the
strongest
covering
the
others.
In order
to
find
and
eliminate
the
maximum
number
of
noise
sources,
you
will
have to start
with
the
strong
sources
and then
work
back.
To
be sure the
noise you
hear
comes
from
your
vehicle
and
not
outside
it,
drive
to
a relatively
quiet
location
(free
of man-made
electrical
interference
such as noisy
power
lines,
industrial
noise or other
vehicles).
Test for
noise with
a weak
signal
on the
channel
and
the
engine
off.
Then
start
the
engine.
Ignition
noise will
probably
be present
at all engine
speeds.
If
it
is severe,
it
may
make
a normally
readable
signal
unreadable.
To
reduce
ignition
noise,
install
resistor-type
spark
plugs
if
these
are not
already
installed.
If non-resistance
ignition
wiring
is used,
install
a 10k-ohm
suppressor
resistor
at each spark
plug
tower
of
the distributor.
Install
a coaxial
capacitor
at the ignition
coil
primary
as close to the coil primary
as possible.
This capacitor
can be purchased
from
an electronics
parts company
or an automotive
electrical
service
company.
A
"whining"
noise
which
varies
with
engine
speed
and
continues
with
the ignition
turned
off
and the vehicle
coasting
in gear is char-
acteristic
of the alternator.
Check and clean it and install
an alternator
filter
(same sources as above).
An
irregular,
clicking
sound
which
disappears
at a slow
idle charac-
terizes
the voltage
regulator.
Install
a 4-ohm
carbon
resistor
as close
to
the
field
terminal
of
the
regulator
as possible,
then
a .002
11
F
capacitor
in series with
and as close to the resistor
as possible.
Con-
nect
the
capacitor
to
ground.
See the detail
drawings
of
Figure
4.
Irregular
popping
noises
which
vary
with
road
surfaces
indicate
static
discharge
at any
of
several
locations
in the
vehicle.
Tighten
loose nuts and bolts and bond
large areas such as the fenders,
exhaust
pipe, firewall,
etc. to the frame
with
lengths of heavy wire
braid.
More
Help
Figure
4 illustrates
these
noise
suppression
steps.
Additional
infor-
mation
is available
in the
Radio
Amateur's
Handbook
published
by
the
ARRL.
