Sigtronics US-12D - Manual (Page 8)

Note that for 2 and 3 above, it will only squeal if a headset is
actually plugged into the specific jack that is wired incorrectly.
PTT Test:
If all above is good, make sure all headsets are plugged into
their respective jacks. Put on the Driver’s headset and posi-
tion the microphone as usual. Press the Driver’s PTT switch.
While continuing to hold down the switch, talk into the mic
and verify that you can still hear yourself. Also, while holding
down the PTT switch, verify that none of the other headset
microphones are active. Release the PTT switch.
Now put on the Officer’s headset, position the microphone,
and press the Officer’s PTT switch. Verify that only the Officer’s
headset microphone is active as his switch is held down.
If the system has a jack and PTT wired up at the vehicles pump
panel, unplug the headset from the Drivers position and plug
it into the pump panels jack. Press and hold down the pump
panel PTT switch. Verify that only the pump panel headset
microphone is active.
If all works fine, skip down to “Electrical Noise Test” on this
page. If anything does not work as above, you have one of
three possible PTT switch wiring errors:
1. PTT line (white/red, white/blue, yellow, or white/green
wires) open or not connected between a PTT switch and
the UltraSound unit.
2. Open or missing return line (black wire) to a PTT switch.
3. Reversed PTT lines. The Drivers PTT line connected to the
Officer’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 UltraSound 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 possi-ble.
This usually means all lights and strobes. Do not turn on
sirens or horns.
6. Put on the Driver’s headset, position the mic, 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 head-
set 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” on page 8. If you did
hear electrical noise, use the following to track down the
problem:
Turn the vehicle power off and disconnect the UltraSound
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 work-
ing.
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/
charging system — most commonly known as alternator
whine. This is only present when the vehicle’s engine is run-
ning 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 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 even-
tually cause other equipment failure as well as shorten the
life of the vehicle’s batteries.
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