Battery charging system
Alternator / generator to battery wiring
Alternator to regulator control wire (generator field wire)
Other regulator wires
Other noise sources
Electric motors
Engine instrumentation
The charging system circuit, consisting of either generator or alternator and a regulator may
also be split into three parts:-
A low pass filter such as that supplied in the interference suppression kit or similar should be
fitted to the main battery lead at the alternator. The filter must be rated for the maximum
current available from the charging system. The earth lug of the filter should be attached to
the alternator body or the engine block.
This wire carries switching pulses that often contribute noise to the receiver. Suppression
using capacitors or filters must not be attempted since damage to the regulator may result.
Separate the wire from all other wiring, keep it as short as possible and, if longer than about
300mm it should be shielded as described above.
These are normally adequately suppressed using good low-inductance bypass capacitors.
To be effective, these capacitors must connect to the wires to be suppressed and to chassis
with very short leads. For this reason, the 'pigtail' style of suppressor capacitor often used
with mf broadcast receivers is generally ineffective at HF.
(windscreen wipers, fans etc.)
Small electric motors can usually be suppressed with good low inductance bypass
capacitors.
Certain types of oil-pressure sensors and voltage regulators used in instrument systems
contain a vibrating or thermal cycling contact. These devices can only be suppressed by
isolating and screening or wiring in the same way as described for the alternator to regulator
control wire. Disc ceramic capacitors with short leads (protected with insulating sleeving)
are frequently useful but to prevent damage to instrument contacts, where the use of bypass
capacitors is attempted, values larger than 1nf should not be used.
BARRETT 950 HF TRANSCEIVER
PAGE 112
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