Sigtronics SPA-4Si - Manual (Page 5)

Figure 7
page 5
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 500
Ω 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 [email protected]. Technicians are available Monday though
Friday 8 am to 4:30 PM Pacific time.
See the OPERATING INSTRUCTIONS for complete operation information.
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 acti-
vated (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.