Sigtronics Dual Bus Kit Installation & Operation Instructions
INTRODUCTION
ATTENTION INSTALLER: To assure a trouble free installation, please
read the entire instructions through once before beginning.
The Sigtronics Dual Bus Kit includes two Model SPA-4Si intercoms
specifically designed for permanent installation in aircraft using dual
(separate) audio buss’ systems (i.e. aircraft with two audio panels).
The SPA-4Si units allow each pilot, operating separate radios, the
convenience of voice activated inter cabin communication. In addition
to operating their respective radio systems independently, the SPA-4Si
units add independent music inputs and full stereo aviation headset
capability. Optional passenger connections allow intercom and stereo
music positions with radio receive — No radio transmit.
The kit consists of two SPA-4Si intercoms (with the option of adding up
to 4 more SPA-4Si units) each with their own operating controls and
radio interface. An interconnect line allows intercom communication
between the units yet keeps the VHF audio systems separate. When
transmitting through their respective radios, each side will hear
the other’s transmission unless transmitting simultaneously. Radio
transmission is also possible through either unit even when the units
are “OFF.”
The SPA-4Si units may also be used as a dual intercom system in aircraft
without dual audio panels. This is convenient where it is desired to
have separate conversations between pilots and passengers. Contact
Sigtronics for information.
GENERAL FEATURES AND SPECIFICATIONS
Voice Activated: Allows “hands free” intercommunication 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 off to reduce background noise. There is no need to raise your
voice or turn your head anymore!
Transmit Capability: Both pilot and co-pilot can transmit to air traffic
control via push-to-transmit switches and headset boom microphones.
The intercom function is automatically disabled during transmit, so that
only the voice of the person transmitting can be heard.
Radio Monitoring Capability: Radio output can be heard whether
intercom power switch is “ON” or “OFF.”
DUAL BUS KIT SYSTEM SPECIFICATIONS
CONFIGURATION – The Sigtronics Dual Bus Kit Intercom system is
specifically designed for multiple audio bus systems. Each SPA-4Si unit
in the kit provides voice activated (VOX) intercom and music input for
up to four headset positions in a small, permanent, panel mounted
installation in the aircraft.
STEREO MUSIC INPUT – Music input accepts standard portable music
headphone or line level outputs. May use one input for all SPA-4Si units
in the system or each SPA-4Si can have a independent music source.
Automobile Speaker level outputs can be adapted for use with SPA4Si intercoms.
COMPATIBILITY – Sigtronics SPA-4Si intercoms have been designed to
operate with all standard general aviation aircraft radios and headsets.
SIZE: Panel 1” x 2.5”. Chassis - 1” high x 2.5” wide x 4” deep.
Can be mounted either horizontally or vertically in the aircraft panel.
WEIGHT: 5.5 ounces (SPA-4Si intercom unit with panel and knobs).
Jacks and wiring harness weigh 7.0 ounces
INPUT POWER: 11 VDC through 32 VDC. Maximum current drain 0.11
Amps
DISTORTION: Less than 1% total harmonic distortion.
WARRANTY: SPA-4Si intercoms are constructed of high quality
components and carry a five year parts and labor warranty.
HARDWARE SUPPLIED
Besides the intercom and instructions, each SPA-4Si unit comes with
the following hardware:
Headphone Output Jacks - Accept standard 0.250” aircraft
stereo headphone plugs. ...........................................................................4
Microphone Input Jacks - Accept standard 0.206” aircraft
microphone plugs. (U93 plug compatible jacks can be used in
place of the jacks provided – monaural installations only). ..........4
Mic Jack Insulating Washers, Flat ............................................................4
Mic Jack Insulating Washers, Shoulder .................................................4
Intercom Panel - lettered on both sides. ..............................................1
Intercom Control Knobs .............................................................................2
Mounting Screws 4-40 x 1/2 .....................................................................2
Drill Template - Adhesive backed hole size pattern for
drilling aircraft panel. ..................................................................................1
Intercom / Aircraft Interface Cable (4 feet long) ...............................1
Headphone / Music Interface Cable (4 feet long) .............................1
Stereo music input jack 3.5mm ...............................................................1
igtronics
S
®
Specialists in “SOUND” Management
178 East Arrow Highway, San Dimas, CA 91773 ( 909 ) 305-9399
SHOULDER
WASHER
FLAT
INSULATED
WASHER
FLAT
METAL
WASHER
NUT
AIRCRAFT
PANEL
RING
BARREL
TIP
MUSIC MUTE OPTIONS
FACTORY DEFAULT - PARTIAL MUSIC MUTE DURING ICS - When listening
to music and someone speaks on the intercom the default factory operation
is to partially mute the music so you can hear the conversation.
FULL MUSIC MUTE DURING ICS OPTION - The music can be completely
muted during intercom conversations. To enable this option, small jumper
wires are installed on the solder side of the circuit board. See page 5.
HIGH NOISE VERSION
Model SPA-4SiH – The “H” version of the SPA-4Si has all the above features
but is specifically configured for very high noise environments.
CHASSIS INSTALLATION
UNIT PLACEMENT
For ease of operation we recommend that you place the pilot’s SPA-4Si
unit on the pilot’s side of the aircraft panel and the co-pilot’s unit should
be placed on his side. This eliminates any confusion about which half of
the system each pilot has to operate. Also, the location selected for each
SPA-4Si unit requires a minimum front panel area of 2-1/2” by 1”. Depth
required behind panel is 4” plus cable access.
CAUTION: Move the aircraft flight controls through the limits of travel while
observing the selected area and making sure that the rear of the intercoms
and cables will not interfere with any aircraft control components.
PANEL PREPARATION EACH UNIT:
1. Position the adhesive drill template on the aircraft panel in the selected
area.
2. Center punch each hole at the cross lines. (Five holes are in a straight line
and equally spaced 0.4” apart)
3. Drill 1/8” pilot holes in all five places.
4. Enlarge holes to 1/4” and 3/8” per the template.
AIRCRAFT
PANEL
DO N OT R EM OV E
THES E NU TS
INTE RC OM
MOUNTING CHASSIS (See Figure 2)
1. Remove the knobs from the Volume and Squelch controls using a 0.05
inch Allen wrench. Remove the nut from the ON/OFF switch. NOTE: DO
NOT REMOVE the nuts from the Volume and Squelch controls.
2. Insert the SPA-4Si unit from the rear of the aircraft panel with the
appropriate arrow on the unit chassis pointing upwards.
3. Install the printed SPA-4Si panel and lightly thread the two 4-40 screws
through the holes in intercom panel. The nuts on the Volume and Squelch
controls will fit inside the 3/8” diameter holes.
4. Tighten the two screws and switch nut.
5. Install the knobs on the Volume (VOL) and Squelch (SQ) 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
INTE RC OM
PANEL
SWIT CH
NUT
4– 40 S CR EW S
KNOB
KNOB
Figure 2
Microphone Jack Figure 3
any aircraft control components. (Note that the jack contacts will expand
when a plug is inserted into the jack and must have clearance to prevent
shorting.)
2. Drill 3/8” diameter holes for headphone jacks and install.
3. Drill 1/2” 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, the location can be
used for intercom with the following changes. The mic jack must be rewired 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 ground wire to the barrel terminal of the mic jack
and connect the other end to Intercom Central ground Point “A”.
4. Install insulating washers as necessary if the barrel of the mic jack is
mounted in metal. For the headphone jack, replace the mono headphone
jack with the stereo headphone jack. Connect the green wire (P2 pin 1)
to the tip connection. Connect the white/green wire (P2 pin 2) to the
ring connection.
WIRING INSTRUCTIONS
Connections should be made as shown in Figure 4 and indicated in Tables
1 and 2. Read also the referenced notes below. If longer wire lengths are
required, use a good quality multi stranded hook-up wire - 22 gauge or
larger. Although not necessary, shielded audio wire can be used if desired.
1. The blue wire (J1 pin 3) must be connected to the aircraft radio headphone
output - NOT the speaker output. NOTE – If aircraft radio volume heard in
the headsets changes significantly when switching the ON/OFF switch
a minor adjustment to the radio receive potentiometer will fix this. See
“INSTALLATION CHECK-OUT AND ADJUSTMENTS” Radio Receive Adjust
section on page 4.
2. Connect all intercom mic jack grounds to a single aircraft chassis ground
point - Intercom Central ground Point “A” - as shown in Figure 4. (Use the
black washers supplied to insulate the intercom mic jacks from aircraft
chassis ground). Note this intercom central grounding point is used to
eliminate 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 Intercom Central Ground
Point “A” on their own individual ground wire. Similarly, all intercom
ground wires (J1 pin 4) and all PTT switch ground returns must also be
connected back to Intercom Central Ground Point “A”. It is not necessary,
however, to connect the headphone jack barrels to Intercom Central
Ground 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 (J1 pins 8, 9) and White/Orange (J1 Pin 11) are only used on
installations that require passenger intercom positions.
page 2
MUSIC SOURCE
CO-PILOT'S
AIRCRAFT RADIO
MIC AUDIO
HEADPHONE AUDIO
BUSS
RADIO MIC KEY
TIP
CO-PILOT
PTT SWITCH
RING
A
TO
AIRCRAFT
HAND MIC
CO-PILOT’S
ADJUST
RADIO RECEIVE
JACK
RING
TIP
BARREL
*
MUSIC
CO-PILOT’S
INPUT JACK
J2
P2
SQ ON VOL
P1
J1 (6) BROWN
J1 (2) WHITE / RED
J2 (5) BLACK
J2 (6) WHITE / VIOLET
SPA-4SiTSO
SPA-4Si
INTERCOM
Stereo
Intercom
J1
J1 (7) RED
J1 (3) BLUE
J2 (2) WHITE / GREEN
J2 (1) GREEN
J2 (4) WHITE / BROWN
J1 (4) BLACK
**
J1 (12) YELLOW
BARREL
A
TO
BARREL
TIP RING TIP
RING
J1 (1) WHITE / BLACK
JACK
HEADPHONE
CO-PILOT
MIC
JACK
BARREL
HEADPHONE
A
TO
BARREL
TIP RING TIP
MIC
RING
J1 (11) WHITE / ORANGE
JACK
PASSENGER 4
JACK
A
TO
BARREL
TIP RING TIP
RING
J1 (8) TAN
JACK
HEADPHONE
PASSENGER 5
BARREL
MIC
JACK
A
TO
BARREL
TIP RING TIP
RING
J1 (9) TAN
JACK
HEADPHONE
PASSENGER 6
BARREL
MIC
JACK
TIP
INTERFACE AREA
AIRCRAFT/INTERCOM
TIP
HEADPHONE AUDIO
MIC AUDIO
RADIO MIC KEY
BUSS
PILOT'S
AIRCRAFT RADIO
MUSIC SOURCE
Figure 4
AIRCRAFT
CO-PILOT’S
PILOT’S
AIRCRAFT
RING
TIP
PILOT
JACK
HEADPHONE
JACK
HEADPHONE
PILOT’S
AIRCRAFT
PTT SWITCH
INTERCOM
JACK
HAND MIC
A
TO
RADIO RECEIVE
(1 AMP)
CIRCUIT
BREAKER
12/28 VDC
POWER BUSS
TO AIRCRAFT
ADJUST
TO J1 (7) RED OF
J1 (2) WHITE / RED
J1 (6) BROWN
P1
SQ ON VOL
J2
P2
*
PILOT’S
MUSIC
INPUT JACK
TIP
BARREL
RING
ANY ADDITIONAL
UNITS ***
J1 (7) RED
J1 (3) BLUE
J1
SPA-4SiTSO
SPA-4Si
INTERCOM
Stereo
Intercom
J2 (5) BLACK
J2 (6) WHITE / VIOLET
A
GROUND
CENTRAL
INTERCOM
POINT
TO J1 (4) BLACK OF
ANY ADDITIONAL
J1 (4) BLACK
J2 (1) GREEN
J2 (2) WHITE / GREEN
J2 (4) WHITE / BROWN
POINT
UNITS ***
J1 (10) WHITE / YELLOW
TO J1 (12) YELLOW
OF ANY ADDITIONAL
UNITS ***
**
**
TO J1 (10) WHITE / YELLOW
OF ANY ADDITIONAL
UNITS ***
J1 (10) WHITE / YELLOW
J1 (12) YELLOW
J1 (1) WHITE / BLACK
RING
TIPRINGTIP
A
TO
BARREL
MIC
JACK
BARREL
PILOT
JACK
HEADPHONE
* MAY USE THE SAME SOURCE FOR ALL UNITS.
** NOT NEEDED IF NO MUSIC INPUT IS ON THE SYSTEM.
*** IN ADDITION TO THE PILOT AND CO-PILOT SPA-4Si UNITS,
UP TO 4 MORE SPA-4Si UNITS MAY BE ADDED FOR A TOTAL
J1 (11) WHITE / ORANGE
RING
MIC
TIPRINGTIP
A
BARREL
TO
HEADPHONE
BARREL
OF 6 UNITS MAXIMUM IN THE SYSTEM.
JACK
PASSENGER 1
JACK
A
TO
J1 (8) TAN
RING
TIPRINGTIP
BARREL
MIC
JACK
BARREL
PASSENGER 2
JACK
HEADPHONE
A
TO
J1 (9) TAN
RING
TIPRINGTIP
BARREL
Sigtronics Dual Bus System Kit
MIC
JACK
BARREL
PASSENGER 3
JACK
HEADPHONE
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
3 Blue *1 Radio Headphone Input Radio Headphone Output
4 Black *2
5 N/C — —
6 Brown
7 Red *3
8 Tan *4
9 Tan *4
10 White/Yellow Music Mute Link White/Yellow of any Other Units
11
White/Orange *4
12 Yellow Bidirectional Intercom Link Yellow of any Other Units
Radio Transmit Key Output Tip Terminal of Aircraft Hand Mic
Intercom Central
Grounding Point “A”
Transmit Mic Audio Output Ring Terminal of Aircraft Hand Mic
12 through 28 VDC Power
Input
Passenger #2 Mic Input Ring Terminal of Passenger #2
Passenger #3 Mic Input Ring Terminal of Passenger #3
Passenger #1 Mic Input Ring Terminal of Passenger #1
Jack, or Key Input of Aircraft Radio
or Audio Panel
Aircraft Chassis Ground
Jack or Mic Input of Aircraft Radio
or Audio Panel
Intercom Circuit Breaker
Intercom Mic Jack
Intercom Mic Jack
Intercom Mic Jack
TABLE 2 - P2/J2 - See Wiring Instructions
PIN WIRE COLOR FUNCTION CONNECT TO
1
G re en * 7
2
White/G reen *7
3 N/C — —
4 White/Brown *5
5 Black *5
6 White/Violet *5
Intercom Right
Headphone Output
Intercom Left Headphone Output
Music Input Left Channel Left Music Source Headphone or
Music Input Common Music Source Common Headphone
Music Input Right
Channel
Tip Terminal of Headphone Jack
Ring Terminal of Headphone Jack
Line output
or Line Output
Right Music Source Headphone or
Line Output
5. Each SPA-4Si unit provides a stereo music input. This music input accepts
portable music Headphone or Line level music sources. The wiring diagram
shows how to wire the SPA-4Si for use with a portable stereo music
source. A small stereo input jack is supplied for this purpose. Connect
the White/Brown, White/Violet, and Black wires to one jack as shown in
Figure 4. Identify the jack terminals
Figure 5
AIRCRAFT PANEL
using Figure 5. Drill a 1/4 inch hole
for the jack and mount on the aircraft
panel. To use, connect an adapter
cable between the music input jack
and the output of the portable stereo.
Suitable cables are available at your
TIP
(RIGHT)
RING
(LEFT)
NUT
local stereo or electronics store as
well as from Sigtronics. Speaker level
output car stereo music sources can
BARREL
(COMMON)
also be used with the SPA-4Si units. A Floating Ground Adapter or a four
wire to three wire converter will have to be used between the Stereo and
the SPA-4Si music input (either separate or single inputs). Figure 6 shows
such an adapter and how it is wired into the SPA-4Si.
-
-
J2 (6) WHITE / VIOLET
J2 (4) WHITE / BROWN
J2 (5) BLACK
To SPA-4S
To SPA-4Si
Figure 6
STEREO
RIGHT
LEFT
+
R
-
+
R
-
R – 100 OHM, 5 WATT RESISTOR
C – 220 MFD, 25 VOLT CAPACITOR
+
C
+
C
NO CONNECTION
6. If using only a single portable music source there are two different methods that can be used. For a system with two SPA-4Si units the easiest way
is to wire just like the wiring drawing and use a mini-jack “Y” or splitter
(available at your local stereo or electronics store). Use the splitter and
dual cables to go from the music source into both SPA-4Si input jacks.
The second way is to use just one of the supplied music input jacks and
connect all inputs to it. Do this by connecting all (J2) White/Violet wires
to the TIP terminal, all (J2) White/Brown wires to the RING, and all (J2)
Black wires to the BARREL. This method will work for systems with two
or more SPA-4Si units.
7. The Sigtronics Dual Bus Kit can be installed as shown for use with Stereo
headsets. Alternatively, monaural general aviation type headsets can
be used. To use monaural headsets follow the installation instructions
as normal except for the wiring of the stereo headphone jacks. Use the
stereo headphone jacks supplied with the Sigtronics SPA-4Si units but
leave the “RING” connections open. Instead connect both headphone
wires to the “TIP” of the respective jacks. Connect both the WHITE/GREEN
and GREEN on to the TIP of the headphone jack.
INSTALLATION CHECK-OUT AND ADJUSTMENTS
After the units are installed, again check that the SPA-4Si unit chassis, jacks,
and wiring harness are clear of all aircraft operating controls and cause no
interference with them.
Next, to check out the SPA-4Si unit installations, 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. 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 headsets, and PTT switches are
connected and functioning properly, switch all SPA-4Si ON/OFF switches
to the “OFF” position. Set both audio panels to “Headphone” position. Then
turn on the aircraft radios as usual, and verify that the pilot and co-pilot can
hear the radios and can transmit using their respective push-to-transmit
switches and headsets. Aircraft radios and both audio panels should operate
exactly as they did before the SPA-4Si units were installed. Aircraft radio
reception should also be heard in the passenger headsets if used. There
should be no intercom between headsets with the SPA-4Si units “OFF”.
Next turn both SPA-4Si units “ON”. Set the SPA-4Si volume controls to midposition. Set SPA-4Si squelch controls fully clockwise. Verify that all headset
positions, including the passenger positions if used, can intercom to each
other.
MIC OUTPUT ADJUST
It may be necessary at this time to adjust the SPA-4Si units mic output to
the aircraft radios. A small adjustable potentiometer is provided inside
the units for this purpose. It is accessible through a hole in the side of the
SPA-4Si 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).
RADIO RECEIVE ADJUST
It may also be necessary to adjust the unit’s radio receive input from the
aircraft radio. A small adjustable potentiometer is provided inside the unit
for this purpose. It is accessible under a sticker on top of the chassis box
(see Figure 4), and can be adjusted with a small blade screwdriver. In the
page 4
event of low aircraft radio volume in the “ON” mode relative to “OFF” mode,
an appropriate adjustment can be made. Clockwise rotation increases
the input level to the SPA 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 all headsets plugged in. (The input is set full CCW which is unity
gain for 500Ω radios). Note: Be sure to replace the sticker when you have
completed the adjustment.
MUSIC (IF USED)
You are now ready to check for proper wiring of the music source. First,
make sure squelch is off (full counter clockwise) and the intercoms are “ON”.
Turn on the music source and listen for music through pilot and co-pilot
headsets, and passenger headsets. There should be music.
If everything checks out, refer to the OPERATING INSTRUCTIONS section
for proper use and other operating modes of the Sigtronics Dual Bus Kit
intercom system. If something does not work as described, 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 SPA-4Si
intercoms or any other Sigtronics product feel free to contact us directly or
E-mail us at tech@sigtronics.com. Technicians are available Monday though
Friday 8 am to 4:30 PM Pacific time.
See the OPERATING INSTRUCTIONS for complete operation information.
Figure 7
FULL MUSIC MUTE DURING ICS OPTION
To select full music mute during intercom, the unit must be removed from
the aircraft. This is done by first removing the volume and squelch control
knobs with a 0.05 inch Allen wrench. Then remove the two mounting screws
and switch nut that holds the unit in the panel. The unit is now free for
removal from the aircraft after disconnecting the cables at the plugs.
To enable this option, modification to the bottom of the units’ circuit
board is required. CAUTION – a qualified technician should perform this
modification. First remove the three screws securing the bottom cover to
the case and carefully lift and remove the cover. Note that the circuit board
does not have to be removed from its case to complete the modifications.
To select full mute during intercom solder the two small-insulated jumper
wires at the locations specified in Figure 7.
Replace the cover and secure it with the three screws as before. Install the
unit back into the panel and plug in the two cables.
OPERATING INSTRUCTIONS
INTRODUCTION
This section describes the operation of the Sigtronics Dual Bus intercom
system. For information on SPA-4Si installation see the INSTALLATION
INSTRUCTIONS section beginning on page 2.
The SPA-4Si intercoms for dual audio buss systems incorporate voice activated (VOX) intercom with “transmit through the aircraft radio capability”
using your push-to-transmit (PTT) switches. In addition they allow for
stereo music input.
CONTROLS
Three controls are provided on each SPA-4Si unit:
ON/OFF Switch - Turns the intercom “ON” or “OFF”.
INTERCOM VOL - Volume Control - Controls the intercom volume. (Except
in OFF mode when the intercom is switched off)
INTERCOM SQ - Squelch Control - Sets the intercom turn-on threshold for
voice activated intercom (VOX) mode.
Each unit will function as an independent intercom with pilot, co-pilot,
and any additional SPA-4Si units having their own ON/OFF switch. When
all intercoms are “ON”, pilot, co-pilot, and passengers (if used) can intercom.
Also, when either pilot or co-pilot transmit over the radio, they will hear
each other. If both transmit simultaneously, neither will hear the other.
The purpose of this feature is to allow independent VHF communication.
Transmitting is also possible with the intercom OFF.
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 SPA-4Si intercoms voice activated (VOX)
feature, the 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 electrical power on, set all
SPA-4Si ON/OFF switches to the “ON” position. Turn the SPA-4Si unit
volume (VOL) controls to the 10 o’clock position.
2. To adjust the intercom squelch controls for voice activated operation
(VOX), it may also be necessary to turn up the intercom volume controls.
Turn all intercom squelch controls all the way counter clockwise. Now,
without speaking, rotate one of the squelch controls clockwise until
you hear the background noise in your headset. Next, using the same
control, rotate counter clockwise small, incremental amounts until the
background noise disappears. (This procedure is necessary because the
squelch is a “fast on, slow off” system). The squelch control is now set on
that intercom unit.
3. Adjust the other intercom squelch controls similarly by turning clockwise
until you hear background noise. Rotate counter clockwise incremental
amounts until the background noise disappears. Small adjustments may
be necessary if aircraft background noise changes significantly - such
as from idle to maximum power.
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.
page 5
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 Volume controls should be set to the minimum
level for best performance. Intercom Volume levels set too high allow excessive background noise to enter the headset. This promotes whispering
into the headset microphone. Excessive background noise and whispering
combine to degrade what is called the “signal to noise ratio”. This decreases
intelligibility and interferes with proper Squelch (VOX) operation.
RADIO TRANSIT MODE
Because of the dual intercom design of the Sigtronics Dual Bus Kit,
transmitting from both pilot and co-pilot positions is possible simultaneously
or one-at-a-time. Each pilot selects the radio he wishes to use via his audio
panel. When he presses his PTT switch, his headset mic is routed through the
intercom to the radio he selected. Only his mic will be live. The microphone
of any passengers connected to the pilot’s side of the system (i.e. the pilot’s
SPA-4Si) will be muted when the pilot transmits. Similarly, when the co-pilot
transmits, only the co-pilot’s mic signal will go out on the radio selected
by the co-pilot. When transmitting, the pilots will hear their own voice via
the aircraft radio side-tone return. If the radio does not provide transmit
side-tone, then they will not hear their voice when transmitting.
RADIO MONITORING
Radio monitoring is automatic. The radio monitor circuit is always active;
even with the SPA-4Si unit power switch “OFF”. Each pilot will only hear the
radio selected by his respective audio panel.
MUSIC OPERATION
Music is controlled at the music source itself. To adjust the music volume
level set the volume control on the music source. Similarly, to turn on or
off the music use the appropriate control on the music source. When the
music source is “ON” the SPA-4Si system automatically mutes and restores
the music to the headsets at the appropriate time. The SPA-4Si default
mode of operation is to partially mute during intercom conversations and
full mute during any aircraft radio communications
MUSIC MUTE OPTIONS
MUSIC MUTE LEVEL DURING ICS - During normal intercom operation
there are two possible muting levels, full or partial. Partial mute is the factory
default. Alternately, “full mute” mode is user selectable prior to intercom
installation. Note: during radio transmission and reception, the music will
always full mute. This is for communication safety reasons.
STEREO MUSIC SYSTEMS
Most automotive stereo units operate from 12V-14V sources. If you want to
use a 12 volt music source in a 28 volt aircraft do not connect them directly
to power. Regulators or converters are available to permit operation from
24V-28V sources.
Some AM-FM music receivers are capable of causing interference with
aircraft COM and NAV receivers. The aircraft panel should be placarded
accordingly. Most player only units (MP3 or CD) do not cause interference
with aircraft receivers.
Line level stereo music outputs can also be used into the SPA-4Si system.
Some line level outputs however, are a fixed level and are not adjusted by
the devices volume control. If this is the case you will not be able to change
the volume of the music you hear in the headsets. Headphone level or
Speaker level outputs would be better in this case.
STEREO HEADSETS
The Sigtronics Dual Bus Kit systems are designed for use with general aviation Stereo headsets with high impedance speakers (300 to 600 ohms).
Headsets with low impedance (less than 100 ohms) speakers should not
be used with SPA-4Si systems intercoms without modification. Contact
Sigtronics for details. In general, headsets with speakers of high and low
impedance and / or unmatched audio efficiencies should not be used
together without modifications.
Sigtronics stereo headsets are specifically designed for the aircraft high
noise environment and give excellent noise attenuation. They also provide full frequency response stereo for maximum enjoyment. They are
compatible with aircraft mic circuits and can be used as general aviation
headsets in aircraft that are not equipped with stereo headphone jacks.
This is because they include a switch to change from “Stereo” to “Monaural”.
No adapters required.
NOTE: General aviation headset (monaural) phone plugs should not be
plugged into SPA-4Si stereo phone jacks. A monaural plug in a stereo jack
shorts out one of the audio channels. This will not damage the SPA-4Si units
in any way but will cause reduced performance. General aviation headsets
may be used only if one of the following three changes are made:
1. Monaural to stereo adapters are used on the headset headphone plugs.
(Only monaural music will be heard.)
2. The general aviation headsets are re-wired for stereo reception.
3. Install the Sigtronics SPA-4Si units for monaural operation. See note 7
in the “WIRING INSTRUCTIONS” section on page 4.
SOLO FLIGHTS
Since the intercoms are not needed during solo flights, they may be turned
to the “OFF” 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-totransmit switch. To hear music, the intercom will have to be in the “ON” mode.
FAIL-SAFE
I
f power to the SPA-4Si units fails, the pilots can still transmit and receive on
the aircraft radio(s) (assuming the radio(s) are still functioning). If a problem
is ever suspected, switch the intercoms “OFF”. 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 this “FAIL-SAFE” or “OFF” mode.
FAA TSO: C50b ENV. CAT (DO-160) CFBBBX
Sigtronics Corporation
178 East Arrow Highway
San Dimas, CA 91773
(909) 305-9399
www.sigtronics.com
spa4si_ins.pdf SPA4SiInst P/N 700141 2-1-2012
igtronics
S
®
Loading...