Suppression
of
Radio
and
TV Interference
Motors
and
speed
controls
of
household sewing machines
are
among
the
electrical equipment which frequently causes
radio
and
TV
interference.
The sparks occurring
at
the commutator
and
the
contacts
are
miniature "jam-
ming stations", which interfere with
radio
and
TV
reception over
the
power
cords
and
through radiation.
The amount
of
interference is determined
by
the
ratio
between
the
useful
energy
received
!b
y
the
transmitter
and
the disturbing energy emitted.
The
same
amount
of
disturbing
energy
which will interfere with the reception
of
a local station only slightly, will interfere much more seriously with
the
re-
ception
of
a
distant
station whose transmitting
power
is
weak.
Our
customers,
therefore, should
be
advised to use
an
outdoor
aerial
for their
radio
and
TV
sets
in
order
to ensure
good
reception also
for
distant stations.
In
Germany,
the
VDE
(Association
of
German
Electrical Engineers)
has
set
the
limits
of
maximum permissible
radio
and
TV
interference
in
the
entir-e fre-
quency
range
from 0.15
to
300 megacycles
per
second. This frequency
range
covers
the
long, medium, short,
and
ultra-short
wave
bands
as
well
as
TV.
The
degree
of
interference has been classified into three groups,
as
follows:
G (coarse)
N (normal)
K (negligible)
The
degree
of
interference
caused
by
our
electrical equipment lies
below
group
N,
which is very favorable.
The whole
problem
of
radio
interference suppression
is
exceedingly difficult.
To ensure a
degree
of
rad
io interference suppression which would
meet
all
conceivable requirements would
be
much
too
expensive
at
present. For this
reason, a compromise
has
been
reached which
is
laid down
in
the
VDE
speci-
fications. These specifications
are
adhered
to
in
making
our
sewing machines
non-static.
Pfaff household sewing machines
have
been
tested
and
approved
by
the
VDE.
As a result, Pfaff
is
authorized
to
state the
degree
of
radio
interference sup-
pression
obtained
on the model
plate:
Normal
FN
59.
Note
To
ensure effective
radio
interference suppression, make sure when repairing
a machine
that
you
use
the
same
radio
noise filters
that
were
installed
in
the
machine originally.
31
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