Sigtronics SPA-400N User manual
The Sigtronics’ SPA-400N is a voice actuated intercom with “transmit
through the aircraft radio capability” using your push-to-talk switch.
Three controls are provided:
Power Switch — Turns unit on and off.
Volume Control — Controls the intercom volume.
Squelch Control — Allows the setting of voice actuated (VOX) operation
of the intercom for variations in background noise levels and differences
in headset microphones.
OPERATING INSTRUCTIONS
I. INTERCOM MODE
A. Put on headset/s and position the boom mic close to the mouth, as
is the practice with a hand-held mic. Voice clarity is best when mic
is at one side of the mouth and 1/4” from the lips.
B. Set audio panel to “Headphone” position, if applicable.
C. Turn power “on” and set Volume Control to a low level. (1/4th to 1/3rd
open for best signal to noise ratio).
D. For voice activated intercom adjust Squelch Control clockwise
until back ground noise becomes audible. Then rotate counter-
clockwise small amounts until the noise diminishes. Now make small,
incremental adjustments until voice triggers unit on. This procedure
is necessary because the squelch system is a “fast on, slow off”
circuit.) Small adjustments may be necessary if aircraft background
noise changes signi cantly. To use the push-to-intercom feature, turn
the squelch control on the intercom fully counter-clockwise. Then to
activate, push the ICS push-to-intercom switch.
II. RADIO TRANSMIT MODE — Transmitting from both pilot and co-pilot
positions is possible on a one-at-a-time basis. The transmitting mic
disables all other mics. When you are ready to talk to ATC, depress the
transmit switch on your yoke and your voice is automatically transmitted
via the aircraft radio.
You will hear your own voice when transmitting via the aircraft radio
side-tone return, If the radio does not have side-tone, then you will not
hear your voice. A minor modi cation to the intercom will enable it to
simulate side-tone.
III. RADIO MONITORING — Radio monitoring is automatic. The radio
monitor circuit is always active; even with intercom power switch
“off”.
IV. SOLO FLIGHTS — Since the intercom is not needed during solo ights,
it may be turned off. The pilot will still hear the aircraft radio, since
this circuit is always active, and the pilot may transmit to ATC via his
push-to-talk switch. (Co-pilot position cannot transmit when intercom
is off).
V. BACK-UP — If a problem is suspected in the intercom, simply turn it
off. You will still receive the aircraft radio and will be able to transmit
from the pilot’s position. The hand mic may also be used, however, the
Transcom should be turned off and you should unplug your boom mic
from the mic jack. (Leave headphone plugged in for radio reception).
CHASSIS INSTALLATION
The Sigtronics’ SPA-400N has been designed to mount either horizontally
or vertically in your aircraft panel. All necessary mounting hardware has
been supplied for a 4-way installation. (A round faceplate is also available
from Sigtronics to t a 2 1/4” round instrument hole).
HARDWARE SUPPLIED
Four Headphone Output Jacks — Accept standard .250” aircraft
headphone plugs.
Four Microphone Input Jacks — Accept standard .206” aircraft microphone
plugs (i.e. ampli ed dynamic or electret). (U93 plug compatible jacks can
be used in place of the jacks provided).
Mic Jack Insulating Washers: 4 shoulder and 4 at.
Panel: Lettered on both sides.
Control Knobs (2), Switch Nut (1), 4-40 Screws (2)
Template: Hole size pattern for drilling aircraft panel.
Aircraft / Intercom interface cable (4 feet long)
The location selected requires a minimum front panel area of 2-1/2” by
1-1/16”. Depth required behind panel is 4-3/16” plus cable access.
Caution: Move aircraft ight controls through limits of travel while
observing selected area to make sure rear of intercom and cable will not
interfere with aircraft control components.
PANEL PREPARATION:
1. Position adhesive template on aircraft panel in selected area.
2. Center punch each hole at cross lines. (The ve holes are in straight
line and equally spaced 0.4” apart.)
3. Drill 1/8” pilot hole all ve places.
4. Enlarge holes to 1/4” and 3/8” per template.
MOUNTING CHASSIS: See Figure 2.
1. Remove nut from Transcom ON-OFF switch bushing.
2. Remove knobs from Volume and Squelch controls. NOTE: DO NOT
REMOVE nuts from Volume and Squelch control potentiometers.
3. Remove two 4-40 panel screws and remove panel from Transcom
chassis.
4. Insert Transcom from rear of aircraft panel with appropriate arrow
pointing upwards.
(continued)
SPA-400N INSTALLATION AND OPERATING INSTRUCTIONS
(For Very High Noise Applications)
AIRCRAFT
PANEL
Figure 2
Figure 3
Microphone Jack
Sigtronics Corporation
178 East Arrow Highway
San Dimas, CA 91773
Phone: (909) 305-9399
E-mail: [email protected]
Web Site: www.sigtronics.com
Figure 1
MOUNTING CHASSIS (continued)
5. Install panel and lightly thread nut on to ON-OFF switch. Nuts and
washers on Volume and Squelch controls should t inside the 3/8”
diameter holes.
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 1
*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 all 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 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 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)
Current Draw: 0.06 amps @ 28 volts
FAA TSO: C50b ENV. CAT (DO-160) CFBBBX
INTERCOM SPA-400
SQ ON VOL
SPA-400N
INTERCOM
Table 1
Plug
Pin # Wire Color Function Connect To:
1White /
Black Pilot Mic Input Ring Terminal of Pilot Intercom
Mic Input Jack
2White /
Red *A Pilot Transmit Switch Input Pilot Transmit Switch (PTT)
(Switch to Ground to Transmit)
3Blue *B Headphone - Radio and
Intercom Outputs
Radio Headphone Output and all
Headphone Jacks
4Black *C Ground Hand Mic Jack Ground Terminal
(Point A)
5White *D Transmit Relay (Key)
Control Output
Tip Terminal of Aircraft Mic Jack or
Key Input of Aircraft Radio or Audio
Panel
6Brown Mic Audio Output
Ring Terminal of Aircraft Mic Jack or
Input of Aircraft Radio
or Audio Panel
7Red *E 12 VDC through 24 VDC
Power Input Intercom Circuit Breaker
8Tan *F Passenger #1 Mic Input Ring Terminal of Passenger #1
Mic Jack
9Tan *F Passenger #2 Mic Input Ring Terminal of Passenger #2
Mic Jack
10 White /
Blue Copilot Transmit Switch Copilot Transmit Switch (PTT)
11 White /
Orange Copilot Mic Input Ring Terminal of Intercom Copilot
Mic Input Jack
12 Violet Push to Intercom Input Push to Intercom Switches
* See Wiring Instructions
SPA-400N Installation Drawing Figure 4
spa-400n.pdf 1-8-2007 Form SPA-400N-IS REV E
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