Suppression Of Radio And Tv Interference - Pfaff 260 Service Manual

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 !by 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 radio 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.
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