Sigtronics US-DR - Manual (Page 8)

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 UltraSound unit is working.
IF YOU CAN HEAR YOURSELF IN THE HEADSET:
1. Then the UltraSound intercom return wire (black) is incor-
rectly 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 insulat-
ing washers or incorrectly installing the washers.
b) The black wire pinched or cut and shorting to the vehi-
cle 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 UltraSound
unit operation. This noise is getting into the unit on the
UltraSound 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/ charg-
ing 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 fre-quency
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 ground-
ing straps.
If servicing the vehicle’s charging system is impracti-
cal, installing a good alternator whine power line filter
between the vehicle power and the UltraSound 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 eventu-
ally 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, how-
ever, 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:
a) Find a better (less noisy) vehicle power source for the
UltraSound unit. Move the UltraSound red wire to
another power buss. Try not to use a power buss that
also runs electrical motors such as fans or light bars with
rotating lights.
b) Move the UltraSound ground connection (green wire)
to another ground point on the vehicle.
c) Install an electrical noise filter on the power line going
to the equipment causing the noise. Contact the company
that makes the offending equipment for a recommendation
on the type of filter to use.
If something does not work as described, go back over the
wiring and correct before going on. If all is well, you can
tighten all headset jacks and secure all jack box covers
with the supplied hardware. Also, tighten and secure all PTT
switches. On the UltraSound unit, turn down the intercom
VOLUME control to approximately the 10 o’clock position.
IV. RADIO HOOK UP
The connection of the UltraSound unit to the vehicle’s radio(s)
should be done by someone familiar with the radio(s) such as
your radio installer. Refer to the UltraSound Wiring Diagram
- Figure 4 on page 5 for US-45S or US-67S units or for US-45D
or US-67D see Figure 5 on page 6. Only the radio functions
are shown for the radio end of the UltraSound Radio Interface
Cable. Because the connector(s) used by radio manufactur-
ers varies widely, you will have to consult the radio manual
or manufacturer for the connector(s) and pin assignments
used. Sigtronics has extensive radio interface experience
and can assist with any question you might have concern-
ing this or any other aspect of the UltraSound system. See
our installation hot line number located on the last page of
this manual.
First plug J2 of the Radio 1 Interface Cable into P2 of the
Intercom. Then using the radio manuals and the UltraSound
Wiring Diagram, identify the correct signal wires or connec-
tor pins to attach the respective UltraSound wires. For most
radios, these connections are at the back of the radio or radio
control head. For some radios, the only place to connect the
MIC HI and LO and PTT HI and LO wires is to the hand-held
microphone connector.* It is best to wire in such a way that
the radio hand microphone can still be used as normal. Make
sure that you do not physically tie the UltraSound MIC LO and
SPEAKER LO wires to the same pin on the radio, even if they
are tied together inside the radio. As in the headset wiring,
the connections between the UltraSound and radios should
be soldered and insulated for reliability. Do not use crimp
type splices. Use a good quality electrical tape or heat shrink
tubing to cover the soldered connections.
* For the more popular radios of this type Sigtronics manu-
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