User's Manual Part 2

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Engine Instrumentation
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.
General Noise Suppression Tips
When searching for sources of noise, some of their characteristics can be helpful in
identification:-
Petrol engine ignition noise and contact breaker noise is a sharp staccato 'plop'
varying with engine speed. It is only with this class of noise that the impulse noise
limiter incorporated within some transceivers is effective
Noise from other sources generally has a more 'mushy' sound. That from the
alternator/generator may only be troublesome over a limited range of engine speed
and can also be influenced by the state of charge of the battery.
The noise from instrument regulators may depend on the battery voltage, the
reading of the instrument and the length of time the system has been switched on.
For this reason, the search for noise sources must be done thoroughly to prevent
noise from apparently reappearing after the installation has been completed.
Electric motors generate a 'whining' sound. Do not forget to check windscreen
wipers, electric fuel pumps, heater and air conditioning fans and other motors which
operate only on an intermittent basis.