Sigtronics S-A-F-E Installation Instructions - Manual (Page 7)

If all works fine, skip down to “Electrical Noise Test” on this.
If anything does not work as above, you have one of three
possible PTT switch wiring errors:
1. PTT line (white/red or white/blue wires) open or not
connected between a PTT switch and the SAFE unit.
2. Open or missing return line (black wire) to a PTT switch.
3. Reversed PTT lines. Officer 1’s PTT line connected to Officer
2’s PTT switch and visa versa.
Electrical Noise Test
The last thing to do before the radios are hooked up to the
unit is a simple noise test to verify system wiring as well as
vehicle electrical system integrity.
1. Unplug all intercom headsets except for the drivers.
2. Make sure all the SAFE panel controls and switches are set
as in “System Setup” on page 6.
3. Start the vehicles engine and let it idle a bit. This is a
stationary test - the vehicle should not be moving and
should be in “PARK” or “NEUTRAL” with brakes set.
4. Close all vehicle windows and doors to eliminate as much
background noise as possible.
5. Turn on as much vehicle electrical equipment as possible.
This usually means all lights and strobes. Do not turn on
sirens or horns.
6. Put on the driver’s headset and make sure the headset
volume control is set to maximum.
7. With the vehicle still in “PARK” or “NEUTRAL” and brakes
set, slowly increase the vehicle engine rpm from idle to
about 1500 RPM and back again. While doing this, listen
for any whine or hum in the headsets. Except for some
possible engine background noise being picked up
from the headset microphone you should not hear any
“Electrical” whine or hum in the headset.
8. Shut off the vehicle engine as well as the lights, strobes,
etc. If, while the engine was running, there was no
electrical noise, skip down to “Radio Hook Up”. If you did
hear electrical noise, use the following to track down the
problem:
Finding The Source of Electrical Noise
Turn the vehicle power off and disconnect the SAFE ground
connection (green wire) from ground. Turn on the vehicle
power (engine off), put on the driver’s headset and see if the
intercom part of the SAFE unit is working.
If You Can Hear Yourself In The Headset:
1. Then the SAFE intercom return wire (black) is incorrectly
grounded to the vehicle chassis. Look for:
a) A headset jack barrel touching the vehicle chassis.
Most common when a headset jack is mounted directly
into the vehicle’s panel without using the supplied
insulating washers or incorrectly installing the washers.
b) The black wire pinched or cut and shorting to the
vehicle chassis. This can be anywhere along the
intercom wiring as the black wire goes to all headset
jacks and PTT switches.
2. Once the problem has been found and fixed, again
make sure that the intercom now does not work with the
green wire disconnected. You could have the black wire
grounded in more than one spot.
3. The next step is to reconnect the green wire and do the
electrical noise test again to assure that you have fixed all
possible noise problems.
If You Cannot Hear Yourself In The Headset:
The intercom wiring is correct, but excessive electrical noise
from the vehicle’s power system is affecting the SAFE unit
operation. This noise is getting into the unit on the SAFE
power wires (red and green). There are basically two types
of power line electrical noise sources:
1. Noise generated directly by the vehicle’s electrical/
charging system - most commonly known as alternator
whine. This is only present when the vehicle’s engine
is running and recognized by the fact that the pitch or
frequency of the whine changes directly with the change
in engine rpm. (Higher frequency at higher engine rpm’s
and lower frequency at lower rpm’s.)
The preferred way to solve this type of problem is to have
the vehicle’s electrical/charging system serviced. The
most common cause of this type of noise is bad diodes
in the vehicle’s alternator. Other possible causes are:
Bad vehicle voltage regulator; Bad alternator or battery
cable connections; Missing or bad engine or alternator
grounding straps.
If servicing the vehicle’s charging system is impractical,
installing a good alternator whine power line filter
between the vehicle power and the SAFE red wire will
usually accomplish the same thing. Do not use the type
of filter that installs on or near the alternator. NOTE: This
solution should not be considered a permanent fix. Vehicle
charging system problems of this type will eventually
cause other equipment failure as well as shorten the life
of the vehicle’s batteries.
2. The other type of noise is that generated by equipment
that uses the vehicle’s power. This type of noise is usually
constant and does not vary with engine rpm. It does,
however, go away completely if the offending equipment
is shut off or disconnected. Electrical motors in fans or light
bars with rotating lights are two common examples.
Several things can be done to rectify this type of electrical
noise:
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