MOUNTING CHASSIS (continued)
6. Select two 4-40 screws through holes in intercom panel. Tighten
ON-OFF switch nut.
7. Install knobs on Volume (VOL) and Squelch (SQ) control shafts using
.050" Allen wrench.
MOUNTING HEADPHONE AND MICROPHONE JACKS:
1. Select mounting areas. (One mic and one headphone jack for each
headset). Again, make sure the jacks will not interfere with aircraft
control components.
2. Drill 3/8" diameter holes for headphone jacks and install.
3. Drill 1/2" diameter holes for mic jacks and install with insulating washers
supplied. (See Figure 3).
WIRING INSTRUCTIONS
Connections should be made as shown in Figure 4 and indicated in Table I
*A. White/red (pilot push-to-talk) must correspond with white/black (pilot
mic input) as shown.
*B. The blue wire from Pin 3 must be connected to the aircraft radio
headphone output- NOT the speaker output.
*C. Connect intercom mic jack grounds to Point A as shown in Figure 4.
(Use black washers supplied to insulate intercom mic jacks from aircraft
chassis ground).
*D. Do NOT connect transmit switches to white (key) wire.
*E. Red wire may be connected to either 12 (14V) or 24 (28V) power source.
No switching or adjustments are required to operate from either source.
*F. Tan wires from Pins 8 and 9 are only used on 4-way installations.
FINAL CHECKOUT AND ADJUSTMENT
After the unit is installed, again check that the intercom chassis, jacks, and
wiring harness are clear of all aircraft operating controls and cause no
interference with them. Check out the intercom functions by following the
Operating Instructions.
It may be necessary at this time to adjust the intercom mic output to the
aircraft radios. A small, square, adjustable trimmer potentiometer is
provided inside the unit for this purpose. It is accessible through a hole in the
side of the case, marked “Mod. Adj.”, and can be adjusted with a
screwdriver. In the event of overmodulation (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 initial installation of the
intercom or if a new radio is installed. (The output is set for unity gain at
Sigtronics).
Weight: Intercom with panel and knobs (4.5 oz.)
Jacks and wiring harness (5.5 oz. maximum)
The SPA-400 is FAA-TSO approved (C-50b).
Env. Cat (D0-160) CFBBBX
PLUG
PIN#
1
2
3
4
5
6
7
8
9
10
11
12
WIRE COLOR
White/Black
White/Red *A
Blue *B
Black *C
White *D
Brown
Red *E
Tan *F
Tan *F
White/Blue
White/Orange
FUNCTION
Pilot Mic Input
Pilot Transmit
Switch Input
Headphone - Radio
and intercom Outputs
Ground
Transmit Relay (Key)
Control Output
Mic Audio Output
12 Through 24 VDC
Power Input
Passenger #1
Mic Input
Passenger #2
Mic Input
Co-Pilot Transmit
Switch
Co-Pilot Mic Input
CONNECT TO:
Ring Terminal of Pilot
Intercom Mic Input Jack
Pilot Transmit Switch (PTT)
(Switch to Ground to Transmit)
Radio Headphone Output and
all Headphone Jacks
Hand Mic Jack Ground
Terminal (Point A)
Tip Terminal of Aircraft Mic Jack
or Key Input of Aircraft Radio or
Audio Panel
Ring Terminal of Aircraft Mic
Jack or Input of Aircraft Radio
or Audio Panel
Intercom Circuit Breaker
Ring Terminal of Passenger #1
Mic Jack
Ring Terminal of Passenger #2
Mic Jack
Co-Pilot Transmit Switch (PTT)
Ring Terminal of Intercom
Co-Pilot Mic Input Jack
No Connection
Table 1 - *See Wiring Instructions
Form SPA-400-IS, Rev.D
