Sigtronics SCI-S4 / SCI-S6 Operating Instructions
Specialists in “SOUND” Management
178 East Arrow Highway, San Dimas, CA 91773 ( 909 ) 305-9399
INTRODUCTION
This instruction sheet describes the operation of the Sigtronics
SCI-S4 / SCI-S6 intercom system. For information on SCIS4 / SCI-
S6 installation see the separate SCI-S4 / SCI-S6 INSTALLATION
INSTRUCTIONS.
The SCI-S series of aircraft intercoms incorporate voice activated
(VOX) intercom with “transmit through the aircraft radio capability”
using your push-to-transmit (PTT) switches. These systems include
three main modes of operation - ALL, ISO, and CREW. In addition
they allow for two separate Stereo music inputs one for the Crew
and one for the Passengers.
CONTROLS
Five controls are provided on the SCI-S units:
ALL/ISO/CREW Switch -
Sets the intercom mode of operation.
PILOT/CO-PILOT VOL -
Volume Control - Controls the intercom
volume for pilot (except in ISO mode when the pilot is switched off
the intercom) and co-pilot. (Does not affect aircraft radio volume.
Set radio volume on radio as normal.)
PILOT/CO-PILOT SQ -
Squelch Control - Sets the pilot (except
in ISO mode) and co-pilot intercom turn-on threshold for voice
activated intercom (VOX) mode.
PASSENGER VOL -
Volume Control - Controls the passenger
intercom volume. (Does not affect aircraft radio volume. Set radio
volume on radio as normal.)
PASSENGER SQ -
Squelch Control - Sets the passenger intercom
turn-on threshold for voice activated intercom (VOX) mode.
SQUELCH INDICATOR LIGHTS -
In addition the SCI-S units
provide two Squelch Indicator Lights - one for the Crew and one for
the Passengers. These lights show when the Crew or Passenger
intercom is active. These indicators greatly simplify the setting of
the intercom Squelch controls.
INTERCOM OPERATION
CAUTION -
As is standard practice with all aircraft avionics
equipment, be sure that the aircraft radio master switch is turned
off when you start up the aircraft engine.
SQUELCH SETTING -
To use the SCI-S intercoms voice activated
(VOX) feature, the Crew and Passengers Squelch Controls will have
to be set. This can be performed by the following procedure:
1. To set the Squelch controls it is helpful to have some background
noise present and music sources off. With aircraft power on,
set the SCI-S ALL/ISO/CREW switch to the “ALL” position - the
preferred mode for setting the squelch. Turn both the SCI-S unit
volume (VOL) controls to the 10 o’clock position.
2. The Squelch controls are set one at a time. To set the Crew
VOX first, turn the Crew Squelch (SQ) control full clockwise and
the Passenger Squelch control full counter-clockwise. Inform
everyone on the intercom to remain silent until you finish setting
the intercom squelch. Set the Crew VOX with the Crew Squelch
control and indicator light...
3. Turn the Squelch control all the way counter-clockwise. At this
point the corresponding squelch indicator light will be off. Now,
without speaking, rotate the Squelch control clockwise just
until you hear the background noise in your headset and the
squelch indicator light turns on. Next, rotate the Squelch counter-
clockwise a small amount and wait (approximately 1 second)
until the background noise disappears - squelch indicator off.
Finally, make small adjustments until your voice triggers the unit
at comfortable speaking levels. This procedure is necessary
because the squelch is a “Fast-on, Slow-off” system. Now with
the Crew squelch set, repeat step 3 for the Passenger VOX with
the Passenger Squelch control and indicator light.
Once set, the intercom stays silent until someone speaks in their
headset microphone (mic). Then it instantly turns on and relays the
conversation. After about a second of no conversation the intercom
goes silent again.
In most aircraft the squelch controls will not need to be set again
unless you change the number or type of headsets used with the
system. In some high noise aircraft it is better to set the squelch
during climb or cruise.
VOLUME SETTING -
The Crew and Passenger Volume controls
should be set to minimum levels for best performance. Intercom
Volume levels set too high allows excessive background noise
into the headsets and promotes whispering into the headset
microphones. These combine to degrade what is called the “signal
to noise ratio” which decreases intelligibility and interferes with
proper Squelch (VOX) operation.
