Lesson 1/Learning Event 3
of spark killer used with DC telegraph and teletypewriter relays or keying
contacts consists of a resistor in series with a capacitor, connected across
the contacts.
The connecting leads must be kept as short as possible.
Teletypewriter transmission measurement must be taken before and after
installation of spark killers to detect any-possible deterioration of
waveshape that may in turn result in garbled or distorted signals (telegraph
distortion). The commutators and sliprings of motors and generators require
only the capacitor for adequate spark suppression.
b. To suppress noise caused by spark ignition systems, installation of
standard suppressors without shielding gives considerable improvement at
frequencies below 30 MHz, and some improvement at higher frequencies.
Shielding of the device causing the noise may be necessary if suppression
does not reduce the noise sufficiently.
The criticalness of joints and
materials in high-tension ignition shielding is greatly reduced by the use
of suppressors.
Army tactical vehicles, engine-driven equipment, and
electrical and electronic equipment are normally suppressed from 0.15 to
1,000 MHz.
c. Radio noise may be "bottled up" within a well-shielded source by
filters across all leads connected to the source.
Typical bypass
capacitors, even with very short leads, are effective up to only a few MHz,
since they become less effective above their self-resonant frequencies.
High-quality feed-through suppression capacitors must be used where HF
suppression is required, because they are effective up to 1,000 MHz.
d. When installing cables within the receiving station, it is advisable
to separate conductors carrying RF signals from all other conductors. It is
also advisable to pass voice and DC signals through separate cables to
prevent crossfire of DC pulses into the voice signals.
Such crossfire
sounds like thumps or clicks in the voice signals. This type of noise is
classified as "impulse" noise.
e. The ground connection of a radio receiver often carries noise into
the receiver.
The best remedy is to provide short, direct, independent
connections from the receiver and from the noise source to separate low-
impedance grounds.
Keep all receiver ground leads physically and
electrically separated from the ground leads of any noise source.
f. Good bonding maintenance and practices are essential to obtain low-
impedance ground connections between equipment or suppressors and vehicles
or frames, thereby preventing generation or spread of radio noise.
Connections should be direct, and
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