SG-2000 MANUAL
89
The SGC Building, 13737 S.E. 26th St. Bellevue, WA. 98005 USA
©1995, SGC, Inc.
TEL: (206) 746-6310 FAX: (206) 746-6384
14.3
Vehicular Noise Sources
There are three kinds of vehicle noise which will be encountered. One is the
ground/static noise which should be eliminated by following the proper
grounding procedures noted above. Second is engine noise and third is
accessory noise. Let's address these step by step:
1.
Diesel engines do not make ignition noise. If you are fortunate enough to
have a diesel which doesn't need high voltage spark plugs, you are one
step closer to a perfect mobile set up. However, even in diesel powered
vehicles, there is still an important source of engine related noise: the
generator or alternator.
To eliminate a good deal of vehicle engine-related noise, it is good
engineering practice to install RF by-pass capacitors at the battery and
across the alternator terminals. The capacitor doesn't need to be especially
large: .01 to .1 micro Farad disk ceramic capacitors with a working voltage
of 100 V will do just fine. We recommend the use of non-polarized
capacitors: these are simpler to install because polarity may be ignored.
2.
Gasoline or natural gas-powered vehicles have high voltage wiring for
ignition spark plugs which causes a small amount of radio frequency
energy to be transmitted each time the cylinder fires. So, on an eight-
cylinder car which is running at 3,000 RPM, there are 6,000 little sparks
every minute. Four cylinder cars emit 3,000 sparks at the same RPM.
The key point of installation here is this: Get the antenna system as far
away from the engine compartment as possible. This is why SGC
developed the QMS (Quick Mount System). Not only does this keep the
coupler to antenna wiring as short as possible, but it also puts another
layer of metal between the noisy engine and the antenna base.
3.
The noisiest wire in the vehicle is the lead from the ignition coil to the
center conductor of the distributor and the wiring in the vicinity of the
distributor itself. If you doubt this, we suggest you invest $10.00 in the
best mobile trouble shooting device made: a small cheap AM radio. All
you need to do to “sniff out” 90% of the vehicle noises you will encounter
is to put this little AM radio to the high end of the broadcast band (1610
KHz) and turn up the volume.
As you get the radio near the ignition wiring you will notice a marked
increase in spark plug noise. Isolating the problem is the first step toward
resolving a noisy engine.
The second step in the “cure” involves the use of what we call “Vitamin
C,” electrical capacitance. Applying a capacitor at the right location will