Sigtronics SCI-4 User manual

Sigtronics SCI Panel Mount Intercom System
INSTALLATION AND OPERATING INSTRUCTIONS Models SCI-4 and SCI-6
Specialists in “SOUND” Management
178 East Arrow Highway, San Dimas, CA 91773 ( 909 ) 305-9399
INTRODUCTION
ATTENTION INSTALLER: To assure a trouble free installation, please
read the entire instructions through once before beginning.
Once again Sigtronics is rst. First with VOX, now rst with dual Squelch
lights. Get instant visual conrmation on who is breaking squelch.
All of our products are “systems designed” to provide reliable, fail-safe
products at the lowest possible cost. And we stand behind our products
to guarantee your satisfaction!
The Sigtronics Models SCI-4 and SCI-6 intercom systems are specically
designed for permanent - panel mounted installation in aircraft. The
SCI units allow both pilot and co-pilot to operate the aircraft radios and
have the convenience of voice activated intra-cabin communication.
Passenger connections are provided that allow up to four additional
intercom positions, depending on model.
SIGTRONICS SCI INTERCOM SYSTEM FEATURES:
VOICE ACTIVATED feature allows “hands free” inter-communication
between pilot(s) and passengers. Start speaking and the intercom
instantly turns on to relay your message clearly to the other headsets;
stop talking and it turns o to eliminate background noise. There’s no
need to raise your voice or turn your head to communicate.
UP TO FOUR POSITION INTERCOM is provided with the model SCI-4.
Model SCI-6 handles up to six positions. “H” Model units for use in high
noise aircraft.
DUAL SQUELCH CONTROL AND INDICATOR LIGHTS - Another
Sigtronics rst. Know instantly who is breaking squelch, crew or pas-
sengers.
TRANSMIT CAPABILITY allows both pilot and co-pilot to transmit to
air trac control via their push-to-transmit switches and headset boom
mics. Depending on the mode selected, intercom function is disabled
during transmission so only the voice of person transmitting is heard.
PILOT ISOLATE MODE - The pilot can set the intercom so that he can
transmit and receive on the aircraft radio(s) independently from the rest
of the intercom. The co-pilot and passengers can still intercom among
themselves and not be heard by the pilot. Conversely, they won’t hear
the aircraft radios or the pilot. This can be an advantage in areas of
busy radio trac.
CREW ISOLATE MODE - The pilot can set the intercom so that the pilot
and co-pilot (crew) can intercom, transmit and receive on the aircraft
radio(s) and not hear the passenger conversations. Conversely, passen-
gers can intercom simultaneously and not be bothered by radio trac
or crew conversations.
RADIO MONITORING capability allows radio output to be heard by the
pilot, whether the SCI unit is in “ALL”, “ISO”, or “CREW” mode.
COMPATIBILITY - Sigtronics SCI intercoms operate with all standard
general aviation aircraft radios and headsets.
FAIL-SAFE feature provides the pilot with the ability to use the aircraft
radios even if power is lost to the intercom.
EASY UPGRADE - In most cases enlarge three holes, add two more,
and re-route three headphone wires in an existing SPA-400 or SPA-600
installation and get the latest technology in aircraft intercoms.
WEIGHT: 7.3 ounces (SCI-4 intercom unit with panel and knobs). Jacks
and wiring harness weigh 6.3 ounces.
SIZE: Panel – 1” x 2½”. Chassis – 1” high x 2½” wide x 6” deep. Can be
mounted either horizontally or vertically in the aircraft panel.
INPUT POWER: 11VDC through 32VDC. Maximum current drain 0.2
Amp (SCI-6).
DISTORTION: Less than 1% total harmonic distortion.
WARRANTY: The SCI units are constructed of high quality components
and carry a ve year parts and labor warranty.
FAA TSO: C-50c
ENVIRONMENTAL: DO-160D
Environmental Category:
A1D1XCAAS2MXXXXXXZBBBBXXXXXXXXXXX
WARNING: This product can expose you to chemicals including
Polyvinyl Chloride, which is known to the State of California to
cause cancer, and Lead, which is known to the State of California
to cause birth defects or other reproductive harm. For more
information go to www.P65Warnings.ca.gov.

OPTION - PILOT TRANSMIT PRIORITY - If the pilot and the copilot key
at the same time (not a common occurrence) the default operation is
that both microphones will go out the aircraft radio to the tower. If you
prefer only the pilot’s microphone active when both press their PTT’s
simultaneously then enable this option. Note - if only one of the pilots
presses his PTT only his
mic will go out over the
radio regardless if this
option is selected or not.
To enable this option, re-
move the four screws on
the bottom of the SCI unit
and remove the cover.
Refer to Figure 1. To en-
able pilot transmit prior-
ity solder a small jumper
between pad “B” and pad
“G”. Replace the cover and
the four screws and tight-
en. Removing this jumper
will deactivate the option.
CHASSISINSTALLATION
To upgrade an existing SPA-400 installation to a SCI-4 or a SPA-600 to
SCI-6 skip to the “UPGRADING A SPA INSTALLATION TO A SCI” section
on page 3. For a completely new intercom installation continue below.
Hardware Supplied
Besides the intercom unit and these instructions, each SCI system comes
with the following hardware:
UNIT PLACEMENT
The SCI unit has been designed to mount either horizontally or vertically
in your aircraft panel.
The location selected for the SCI unit requires a minimum front panel
area of 2½” by 1”. Depth required behind panel is 6” plus cable access.
CAUTION: Move the aircraft ight controls through the limits of travel
while observing the selected area and making sure that the rear of the in-
tercom and cable will not interfere with any aircraft control components.
Panel Preparation
1. Position the adhesive drill template on the aircraft panel in the se-
lected area.
2. Center punch each hole at the cross lines. (Five holes are in a straight
line and equally spaced 0.4” apart, two holes are 0.8” apart).
3. Drill ⁄” pilot holes in all seven places.
4. Enlarge two holes to ⁄”, one hole to ⁄”, and two holes to ⁄” per
the template.
Mounting Chassis (See Figure 2)
1. Remove the knobs from the Volume and Squelch controls using a
0.050” Allen wrench. NOTE: DO NOT REMOVE the nuts from the Vol-
ume/Squelch, or ALL/ISO/CREW controls.
2. Insert the SCI unit from the rear of the aircraft panel with the appropri-
ate arrow on the unit chassis pointing upwards. Make sure the squelch
indicator lights have unrestricted movement through aircraft panel.
3. Install the printed SCI panel and lightly thread the two 4-40 screws
through the holes in intercom panel. The nuts on the Volume/Squelch
and ALL/ISO/CREW controls will t inside the ⁄” and ⁄” diameter
holes.
4. Tighten the two screws.
5. Install the knobs on the Volume (VOL) and Squelch (SQL) control shafts
and tighten the Allen screws.
Mounting Headphone And Microphone Jacks (See Figure 3)
1. Locate the mounting areas. (One mic and one headphone jack required
for each headset). Again, make sure that the jacks will not interfere
with any aircraft control components. (Note that the jack contacts will
expand when a plug is inserted into the jack.)
2. Drill ⁄” diameter holes for headphone jacks and install.
3. Drill ½” diameter holes for the mic jacks and install with the insulating
washers supplied. (See Figure 3)
Note: If the aircraft already has pilot headset jacks, they can be used for
intercom, however, the mic jack must be re-wired as follows:
1. Remove any existing wires from the tip, ring, and barrel connections.
2. Connect the intercom white/black wire to the ring terminal.
3. Connect one end of a wire to the barrel terminal of the mic jack and
connect the other end to Point “A”.
4. Install insulating washers as necessary if the barrel of the mic jack is
mounted in metal.
For the headphone jack, remove any existing wires from the tip connec-
tion. Connect the green wire (J2 pin 1) to the tip connection.
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SCI-4 SCI-6
Headphone Output Jacks - Accept standard
0.250” aircraft headphone plugs. 4 6
Microphone Input Jacks - Accept standard 0.206”
aircraft microphone plugs. (U93 plug compatible
jacks can be used in place of the jacks provided).
4 6
Mic Jack Insulating Washers, Flat 4 6
Mic Jack Insulating Washers, Shoulder 4 6
Intercom Panel - lettered on both sides. 1 1
Intercom Control Knobs 4 4
Mounting Screws 4-40 x 1/2 2 2
Drill Template - Adhesive backed hole size pattern
for drilling aircraft panel. 1 1
Aircraft/Intercom Interface Cable
(4 feet long) 1 1
Headphone/intercom Interface Cable
(4 feet long) 1 1

SHOULDER
WASHER
FLAT
INSULATED
WASHER
FLAT
METAL
WASHER
NUT
AIRCRAFT
PANEL
RING
BARREL
TIP
Figure 3
Microphone Jack
KNOB
KNOB
Figure 2
AIRCRAFT PANEL INTERCOM PANEL
DO NOT REMOVE
THESE NUTS
SCI INTERCOM CHASSIS
4-40 SCREWS
UP
RX. ADJ. MOD. ADJ.
WIRING INSTRUCTIONS
Connections should be made as shown in Figure 4 and indicated in Table
1 and 2. If longer wire lengths are required, use a good quality hook-up
wire - 22 gauge or larger. Although not necessary, shielded audio wire
can be used if desired. This can simplify the wiring process.
*1. The blue wire from Pin 3 must be connected to the aircraft radio
headphone output - NOT the speaker output.
*2. Connect all intercom mic jack grounds to a single aircraft chassis
ground point - Point “A” - as shown in Figure 4. (Use the black wash-
ers supplied to insulate the intercom mic jacks from aircraft chassis
ground). Note this intercom central grounding point is used to elim-
inate any unwanted electrical noises, such as alternator whine or
strobe noise, from being induced into the intercom system through
the grounds. All intercom mic jack barrels must be insulated from
ground where they are mounted and connected back to Point “A” on
their own individual ground wire. Similarly, both intercom ground
wires (pin 4) and the push-to-transmit switch grounds must also be
connected back to Point “A”. It is not necessary, however, to connect
the headphone jack barrels to Point “A”. They can either be grounded
where they are mounted or some place nearby.
*3. The red wire may be connected to either 12V (14V) or 24V (28V)
power source. No switching or adjustments are required to operate
from either source.
*4. Tan wires (pins 8 and 9) are only used on installations that require
extra intercom positions.
*5. Provided on SCI-6 units only.
SkiptotheINSTALLATIONCHECKOUTANDADJUSTMENTSsectiononpage5.
UPGRADING A SPA
INSTALLATION TO A SCI
Chassis Mounting
The SCI-4 is specically designed to easily
replace a SPA-400. Similarly, the SCI-6 can
replace a SPA-600. The panels are exactly
the same dimensions (1” x 2½”), however
the SCI units are 1¾” longer than the SPA
units. You will have to make sure that you
have the extra depth required behind your
panel. Five mounting holes are exactly in
the same positions. The center hole will
have to be enlarged from ¼” to ⁄”, the
two outer holes will have to be enlarged
to ⁄”, and two additional holes drilled to
⁄” (As per template).
To upgrade, rst remove the SPA unit from the aircraft panel. This is done
by unscrewing the two Phillips head screws and the nut on the ON/OFF
switch. Remove the printed SPA panel. Pull the SPA unit out and unplug
the white connector from the wiring harness. Next, drill the center hole
in the aircraft panel out to ⁄”. Then drill the two outer holes to ⁄”, then
use template to mark the position of the nal two holes and drill. Finally
mount the SCI chassis (see Figure 2 on page3):
1. Remove the knobs from the Volume and ALL/ISO/CREW controls us-
ing a 0.050” Allen wrench. NOTE: DO NOT REMOVE the nuts from the
Volume/Squelch (VOL/ SQ) or ALL/ISO/CREW controls.
2. Insert the SCI unit from the rear of the aircraft panel with the appropri-
ate arrow on the unit chassis pointing upwards. The squelch indicator
lights (LED’s) should easily t through their respective holes.
3. Install the printed SCI panel and lightly thread the two 4-40 screws
through the holes in intercom panel. The nuts on the Volume/Squelch
and ALL/ISO/CREW controls should t inside the aircraft panel holes.
4. Tighten the two screws. Make sure LED’s have unrestricted movement
in aircraft panel holes.
5. Put the knobs on the Volume and Squelch control shafts and tighten
the Allen screws.
Wiring Change
The wiring changes to an existing SPA installation is as follows. Re-wire
the pilot, co-pilot, and passenger(s) headphone lines. You will not need
the 4 foot interface cable (12 or 15 pin) that comes with the SCI system.
You will use the SPA harness already in the aircraft and the 4 foot head-
phone/intercom interface cable (3 pin).
In an SPA installation, the tip terminals of the pilot, co-pilot, and pas-
senger headphone jacks are wired to the blue wire (pin 3). They need
to be disconnected from there and connected to their respective pins
on the headphone/intercom interface harness. (See Figure 4 on page
4). Make sure that the blue wire (pin 3) is still connected to the tip of the
radio headphone line.
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ALL
ISO
CREW
SCI-4
Pilot/CoPilot Passenger
Made in U.S.A.
INTERCOM
CIRCUIT
BREAKER
(1 AMP)
Q
Volume
S
12345
AIRCRAFT RADIO
NOTES
* USED IN SCI-6 INSTALLATIONS ONLY.
** IF PILOT PTT SW IS CONNECTED TO THE
AIRCRAFT HAND HAND MIC JACK, IT MUST
BE DISCONNECTED AND CONNECTED TO
THE WHITE/RED WIRE AS SHOWN.
AIRCRAFT CHASSIS GROUND.
TO AIRCRAFT
POWER BUSS
12/28 VDC CENTRAL
GROUND
POINT)
AIRCRAFT
HAND MIC
JACK
AIRCRAFT
HEADPHONE
JACK
POINT
AIRCRAFT / INTERCOM INTERFACE AREA
(INTERCOM
A
PILOT
PTT SWITCH
CO-PILOT
PTT SWITCH
HEADPHONE AUDIO
MIC AUDIO
RADIO MIC KEY
J1 (1) WHITE/BLACKJ2 (1) GREEN
J1 (11) WHITE/ORANGE
SCI-4 or SCI-6
INTERCOM
J2 (2) GRAY
TO
TO A
A
J1 (2) WHITE / RED **
J1 (3) BLUE
J1 (6) BROWN
J1 (7) RED
J1 (4) BLACK
J1 (10) WHITE / BLUE
J1 (5) WHITE
J1 (13) TAN *
J1 (14) TAN *
J1 (8) TAN
J1 (9) TAN
J2 (3) YELLOW
MIC
JACK
HEADPHONE
JACK
PILOT
P1
J1
P2
J2
BARREL
TIP RING
BARREL
TIP
TO A
MIC
JACK
TO A
HEADPHONE
JACK
BARREL
TIP RING
BARREL
CO-PILOT
TIP
MIC
JACK
HEADPHONE
JACK
MIC
JACK
HEADPHONE
JACK
PASSENGER 4 *PASSENGER 3 *
MIC
JACK
HEADPHONE
JACK
PASSENGER 2
BARREL
TIP RING
BARREL
TIP
TO ATO ATO A
BARREL
TIP RING
BARREL
TIP
MIC
JACK
TO A
HEADPHONE
JACK
PASSENGER 1
BARREL
TIP RING
BARREL
TIP
BARREL
TIP RING
BARREL
TIP
TIP RING TIP
Figure 4
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TABLE 2 – P2 / J2 – See Wiring Instructions
PIN WIRE COLOR FUNCTION CONNECT TO
1Green Pilot Intercom Headphone Output Tip Terminal of Pilot Headphone Jack
2Gray Co-Pilot Intercom Headphone Output Tip Terminal of Co-Pilot Headphone Jack
3Yellow Passenger Intercom Headphone Output Tip Terminal of Passenger Headphone Jacks
TABLE 1 – P1 / J1 – See Wiring Instructions
PIN WIRE COLOR FUNCTION CONNECT TO
1 White / Black Pilot Mic Input Ring Terminal of Pilot Mic Jack
2 White / Red Pilot Transmit Switch Input Pilot Transmit Switch (PTT) (Switch to Ground to Transmit)
3Blue *1 Radio Headphone Input Radio Headphone Output
4Black *2 Intercom Central Grounding Point “A” Aircraft Chassis Ground
5White Radio Transmit Key Output Tip Terminal of Aircraft Hand Mic Jack, or Key Input of Aircraft Radio or Audio Panel
6Brown Transmit Mic Audio Output Ring Terminal of Aircraft Hand Mic Jack or Mic Input of Aircraft Radio or Audio Panel
7Red *3 12 through 28 VDC Power Input Intercom Circuit Breaker
8Tan *4 Passenger #1 Mic Input Ring Terminal of Passenger #1 Intercom Mic Jack
9Tan *4 Passenger #2 Mic Input Ring Terminal of Passenger #2 Intercom Mic Jack
10 White / Blue Co-Pilot Transmit Switch Input Co-Pilot Transmit Switch (PTT) (Switch to Ground to Transmit)
11 White / Orange Co-Pilot Mic Input Ring Terminal of Co-Pilot Mic Jack
12 N/C None No Connection
13 Tan *5 Passenger #3 Mic Input Ring Terminal of Passenger #3 Intercom Mic Jack
14 Tan *5 Passenger #4 Mic Input Ring Terminal of Passenger #4 Intercom Mic Jack
15 N/C *5 None No Connection

INSTALLATION CHECK-OUT AND ADJUSTMENTS
After the unit is installed, again check that the SCI unit chassis, jacks,
and wiring harness are clear of all aircraft operating controls and cause
no interference with them. Next, to check out the SCI unit installation,
plug in all the headset mic and phone plugs into the respective intercom
jacks. Put on the pilot’s headset and position the boom mic close to the
mouth, as is the practice with a hand-held mic. Voice clarity is best when
the mic is at one side of the mouth and ¼” 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 pull-
ing 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 passen-
ger 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 (See Figure 2). 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 (See Figure 2). 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 INSTRUCTIONS on
page 6 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 [e-mail]. Technicians are available Monday
though Friday 8 am to 4:30 PM Pacic time.
This concludes the installation check-out.
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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 aect 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 aect 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 o 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
nish 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 o. 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-o” 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 ight. 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 microphones of the co-pilot
and any passengers will be muted when the pilot transmits. Similarly,
when the co-pilot transmits, only the co-pilots mic will go out on the
radio. Depending upon which priority mode is selected, only the pilot or
both will go out when both PTT switches are pressed at the same time.
When transmitting, everyone on the intercom will hear the transmitting
pilots voice via the SCI sidetone return.
CREW MODE - When the SCI is in the “CREW” mode, transmitting from
both pilot and co-pilot positions are possible. The pilot selects the appro-
priate 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 microphone of the co-pilot will be muted
when the pilot transmits. Similarly, when the co-pilot transmits, only the
co-pilots mic will go out on the radio. Depending upon which priority
mode is selected, only the pilot or both will go out during simultaneous
keying of the PTT switches. When transmitting, the pilots will hear their
own voice via the SCI sidetone return. In this mode, the passengers will
still have the ability to intercom among themselves and not be bothered
by radio trac interruptions or crew intercom conversation. Similarly,
the pilots will not hear the passenger’s conversations.
ISO MODE - When the SCI is set to the “ISO” mode, only the pilot can
transmit and receive on the aircraft radio(s). The pilot will not hear
intercom and cannot talk to the other headsets. The co-pilot and pas-
sengers still have intercom, but do not hear the radios. If the radio does
not provide transmit sidetone, then the pilot will not hear his voice in
the “ISO” mode.
Solo Flights
Since the intercom is not needed during solo ights, it may be turned
to the “ISO” position. The pilot will still hear the aircraft radio(s), since
this circuit is always active, and may transmit to ATC via his headset and
push-to-transmit switch. If the radio does not provide sidetone, then
switch intercom mode to “CREW”.
Fail-Safe
If power to the SCI unit fails, the pilot can still transmit and receive on the
aircraft radio(s) (assuming the radio(s) are still functioning). Additionally,
if a problem is ever suspected in the intercom, switch to “ISO” mode
or remove power to unit. In this mode you will still be able to transmit
and receive on the aircraft radio(s) from the pilot’s position. If the radio
does not provide sidetone, then the pilot will not hear his voice in the
“FAIL-SAFE” or “ISO” mode.
Sigtronics Corporation
178 East Arrow Highway
San Dimas, Ca 91773
909) 305-9399
www.sigtronics.com
SCI-4_REV-E_Installation_Operating.pdf 8-8-2023 P/N 700110
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