2
environments
such as open cockpit aircraft, warbirds, and ultra-
lights. In addition to special circuitry that improves intercom per-
formance in high noise aircraft, the SPA-4SN has a Push-to-
intercom mode for applications where voice activated (VOX) in-
tercom operation is not desired.
CHASSIS INSTALLATION
To upgrade an existing SPA-400 installation to a SPA-4S skip to
the “UPGRADING A SPA INSTALLATION TO A SPA-4S” section
on page 4. For a completely new intercom installation, continue
below.
UNIT PLACEMENT
The SPA-4S unit has been designed to mount either horizontally
or vertically in your aircraft panel. The location selected for the
SPA-4S 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 intercom and cable will not interfere with any aircraft
control components.
PANEL PREPARATION:
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.
MOUNTING CHASSIS
(See Figure 2)
1. Remove the knobs from the Volume and Squelch controls us-
ing a 0.050" 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-4S unit from the rear of the aircraft panel with
the appropriate arrow on the unit chassis pointing upwards.
3. Install the printed SPA-4S 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 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 re-wired as follows:
1. Remove any existing wires from the tip, ring, and barrel con-
nections.
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 following Table
2. If longer wire lengths are required, use a good quailty multi-
stranded hook-up wire - 22 gauge or larger. Although not neces-
sary, shielded audio wire can be used if desired.
RING
BARREL
SHOULDER
WASHER
FLAT
INSULATED
NUT
AIRCRAFT
PANEL
FIGURE 3
WASHER
TIP
MICROPHONE JACK
FLAT
WASHER
METAL
DO NOT REMOVE
THESE NUTS
AIRCRAFT
PANEL
INTERCOM
PANEL
SWITCH
NUT
KNOB
4-40 SCREWS
KNOB
INTERCOM
FIGURE 2
