Sigtronics SCI-6 - Manual (Page 5)

held mic. Voice clarity is best when the mic is at one side of the
mouth and 1/4” from the lips.
To assure that the aircraft radios, pilot’s headset, and PTT switch
are connected and functioning properly, remove power to the SCI
by pulling intercom circuit breaker. If applicable, set the aircraft
audio panel to “Headphone” position. Then turn on the aircraft
radio(s) as usual, and verify that the pilot can hear the radios and
can transmit using his push-to-transmit switch and headset. Aircraft
radio(s) and audio panel should operate exactly as they did before
the SCI system was installed. Aircraft radio reception should not be
heard in the co-pilot or passenger headsets. There should be no
intercom between headsets with no power to the SCI unit.
Next restore power to the SCI unit. Switch ALL/ISO/CREW
control to the “ALL” position. Set the SCI volume controls to mid-
position. Set both SCI squelch controls fully clockwise. Verify that
all headset positions can now intercom with each other, including
the passengers. Verify that both pilot and co-pilot can operate the
aircraft radio(s). In this mode all headsets on the intercom will hear
the aircraft radio(s).
It may be necessary at this time to adjust the SCI unit mic output
to the aircraft radios. A small adjustable potentiometer is provided
inside the unit for this purpose. It is accessible through a hole
in the side of the SCI chassis. It is marked “Mod. Adj.”, and can
be adjusted with a small blade screwdriver. In the event of over-
modulation (garbled) or reports of weak transmissions over the
aircraft radio, an appropriate adjustment can be made. Clockwise
rotation increases the output level to the aircraft radio mic input.
Counter-clockwise rotation decreases modulation level. This
adjustment sometimes needs to be made after the initial installation
of the intercom or if a new radio is installed. (The output is set for
unity gain at Sigtronics).
It may also be necessary to adjust the SCI unit radio receive input
from the aircraft radio. A small adjustable potentiometer is provided
inside the unit for this purpose. It is accessible through a hole in the
side of the SCI chassis. It is marked “RX Adj.”, and can be adjusted
with a small blade screwdriver. In the event of low aircraft radio
volume in the “ALL” or “CREW” mode relative to “ISO” mode, an
appropriate adjustment can be made. Clockwise rotation increases
the input level to the SCI radio receive input. Counter-clockwise
rotation decreases input level. This adjustment sometimes needs
to be made after the initial installation of the intercom or if a new
radio is installed that has a low output impedance or low output
power. The adjustment is best made with the pilot and co-pilot
headsets plugged in. (The input is set full CCW which is unity gain
for 500Ω radios).
If everything checks out, refer to the OPERATING IN-
STRUCTIONS below for proper use and other operating modes
of the Sigtronics SCI intercom system. If something does not
work as above, carefully go over the intercom wiring again. If
something is still not right or you have any questions regarding
the installation and operation of the Sigtronics SCI intercom or any
other Sigtronics product feel free to contact us directly or email us
at [email protected]. Technicians are available Monday though
Friday 8 am to 4:30 PM Pacific time.
This concludes the installation check-out.
OPERATING INSTRUCTIONS
The Sigtronics SCI-4/SCI-6 is a voice activated (VOX) intercom
for aircraft with “transmit through the aircraft radio capability” using
your push-to-transmit switches. Three controls are provided on the
SCI 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) 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.
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.
INTERCOM OPERATION
Intercom operation and adjustment can be performed by the
following procedure:
1. With aircraft power on, set the SCI ALL/ISO/CREW switch to the
“ALL” position - the preferred mode for setting the squelch.
2. Turn the SCI unit volume controls to the 10 o’clock position.
Turn the crew squelch control full clockwise and the passenger
squelch control full counter-clockwise. Inform passengers to
remain silent until you finish setting the intercom squelch.
3. To adjust the intercom squelch control for voice activated
operation (VOX), it is helpful to have some background noise
present. Turn intercom crew SQuelch control all the way
counter-clockwise. Now, without speaking, rotate the Squelch
control clockwise until you hear the background noise in your
headset, at this point the crew squelch indicator light will be
on. Next, rotate it counter-clockwise a small amount and wait
(approximately 1 second) until the background noise disappears
and the squelch indicator light is 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 squelch.
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 level won’t need to be set again until
the next flight. In some high noise aircraft it is better to set the
squelch during climb or cruise.
INTERCOM MODES
ALL MODE - When the SCI is in the “ALL” mode, transmitting
from both pilot and co-pilot positions is possible. As normal, the
pilot selects the appropriate radio he wishes to use. When the pilot
presses his PTT switch, his headset mic is automatically routed
through the intercom to the radio. Only his mic will be live. The mi-
crophones of the co-pilot and any passengers will be muted when
the pilot transmits. Similarly, when the co-pilot transmits, only the
page 5