SDB-800 - Dallas Avionics

SDB-800 - Dallas Avionics
Model SDB-800 Installation and Operating Instructions
A Voice Activated Intercom System for Aircraft with Dual Audio Panels!
The Model SDB-800 is an intercom system specifically
designed for permanent installation in aircraft using dual
(separate) audio buss’ systems (i.e. aircraft with two audio
panels.) The SDB-800 allows both pilots, operating separate
radios, the convenience of voice activated intercabin
communication while operating their respective radio systems
independently. Optional passenger connections allow up to six
“intercom only” positions.
The system consists of two modified SPA-400 units with their
own operating controls and radio interface. An interconnect line
allows intercom communication between the two units yet
keeps the two 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 SDB-800 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
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-talk switches and headset boom
microphones. The intercom function is automatically disabled
during transmitting, 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.”
Compatibility: All Sigtronics’ intercoms operate with all standard
aircraft headsets.
Failsafe: Provides ability to transmit through aircraft radio even if
the intercoms are “OFF.”
Weight: 4.5 ounces each (main chassis with panel and knobs.)
Jacks and wiring harness for four headset positions weigh 5.5
Size of each unit: Panels - 1" x 2.5". Chassis - 4" deep, 2.5" wide,
1" thick. They can be mounted either horizontally or vertically in the
aircraft panel.
Input Power: 12V through 28 VDC. Maximum current drain for
both units is 1/10 amp. (0.1A).
Distortion: Less than 1% total harmonic distortion.
Environmental: Meets requirements of TSO-C50b.
Warranty: The SDB-800 is constructed of high quality components
and carries a one year parts and labor warranty.
Made in U.S.A. with quality components
949 N. Cataract Ave. #D, San Dimas, California 91773 · PHONE (909) 305-9399
The Sigtronics’ Model SDB-800 consists of two complete units.
Figure 4 shows that each unit is completely independent from the
other except for power, ground, and the yellow wire. Each half of the
SDB-800 is designed to mount either horizontally or vertically in
your aircraft panel. All necessary mounting hardware is supplied for
2-way through 8-way installation.
7. Install knobs on Volume (VOL) and Squelch (SQ) control
shafts using .050" Allen wrench.
8. Repeat for other SDB unit.
Hardware Supplied:
Eight Headphone Output Jacks - Accept standard .250" aircraft
headphone plug.
Eight Microphone Input Jacks - Accept standard .206" aircraft
microphone plugs (i.e. carbon, amplified dynamic or electret). (U93
plug compatible jacks can be used in place of the jacks provided).
Mike Jack Insulating Washers: 8 shoulder and 8 flat.
Two SDB-800 intercom panels lettered on both sides.
Control Knobs (4), Switch Nuts (2) 4-40 Screws (4)
Two drill templates: Hole size pattern for drilling aircraft panel.
Two Aircraft/Intercom interface cables (4 feet long)
For ease of operation we recommend that you place the pilot’s SDB
unit on the pilot’s side of the aircraft panel and the copilot’s unit
should be placed on his side. This eliminates any confusion about
which half of the SDB-800 system each pilot has to operate. Also,
the location selected for each SDB unit requires a minimum front
panel area of 2-1/2" by 1- 1/16". Depth required behind panel is 43/16" plus cable access.
CAUTION: Move aircraft flight controls through limits of travel to
make sure rear of intercoms and cables will not interfere with
aircraft control components.
1. Locate mounting areas. (One mike 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 ½" diameter holes for mike jacks and install with
insulating washers supplied. (See Figure 3).
NOTE: If the aircraft already has pilot headset jacks, they can be
used for the intercoms, but they must be rewired as follows:
Mike Jack:
1. Remove any existing wires from the tip, ring, and barrel
2. Connect the intercom white/black wire to the ring terminal.
1. Position adhesive template on aircraft panel in selected areas.
3. Connect one end of a ground wire to the barrel terminal of the
mike jack and connect the other end to Point A.
2. Center punch each hole at cross lines. (The five holes are in
a straight line and are equally spaced 0.4" apart).
3. Drill 1/8" pilot hole all five places.
4. Enlarge holes to 1/4" and 3/8" per template.
5. Repeat above for the other SDB unit
4. Install insulating washers as necessary if the barrel of the
mike jack is mounted in metal. These are not necessary for
function, however they reduce the possibilities of ground loop
induced noise.
For the headphone jack: add the appropriate blue wire to the tip
terminal. No need to remove existing wires on the headphone jack.
1. Remove nut from SDB unit ON-OFF switch bushing.
2. Remove the 4-40 screws on either side of switch.
3. Remove Volume and Squelch control knobs. NOTE: DO NOT
REMOVE nuts from Volume and Squelch control
4. Insert SDB unit from rear of aircraft panel with appropriate
arrow pointing upwards.
5. Install panel and lightly thread nut on to ON-OFF switch. Nuts
and washers on Volume and Squelch controls should fit inside
the 3/8" diameter holes.
6. Install two 4-40 screws through holes in intercom panel.
Tighten ON-OFF switch nut.
Figure 4 and Table 1 show how to make the wiring connections. If
you need longer wire lengths, use good quality hook-up wire, 22
gauge or larger. Shielded audio wire can be used, however, it is not
necessary. This can simplify the wiring process.
*1. The blue wire from Pin 3 must be connected to the aircraft
radio headphone output - NOT the speaker output.
*2. Connect all intercom mike jack grounds to a single aircraft
chassis ground point - Point “A” - See Figure 4. (Use the
black washers supplied to insulate intercom mike jacks from
aircraft chassis ground)."
*3. Do NOT connect transmit switches to white (key) wire.
*4. Red wire may be connected to either 12V (I 4V) or 24V (28V)
power source. No switching or adjustments are necessary to
operate from either source.
*5. Tan wires (pins 8 and 9) and white/orange wires (pin 10)
are only used on installations that require extra intercom
**NOTE: Use this intercom central grounding point so that no unwanted
electrical noise, such as alternator whine or strobe noise, will be induced
into the intercom system through the grounds. Each intercom mike jack barrel should be insulated from ground and connected back to Point ”A" on its
individual ground wire. Similarly, both intercom ground wires (pin 4) and the
push-to-talk switch grounds should be connected back to Point “A”. It is not
necessary, however, to connect the headphone jack barrels to Point “A”.
They can be grounded where you mount them or some place nearby.
After installing the units, again check that the SDB chassis, jacks,
and wiring harnesses are clear of all aircraft operating controls and
cause no interference with them. Check out the SDB unit functions
by following the instructions:
1. Plug in all the headsets mike and phone plugs into the respective
intercom jacks. Put on headset/s and position the boom mike close
to the mouth, as is the practice with a hand-held mike. Voice clarity
is best when mike is at one side of the mouth and 1/4" from the lips.
2. To assure that the aircraft radios, pilot’s headsets, and PTT
switches are functioning properly, turn both SDB units’ ON/OFF
switches to “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-talk switches and headsets. Aircraft radios and
both audio panels should operate exactly as they did before the
SDB-800 system was installed. Aircraft radios reception should
also be heard in the passenger headsets (if applicable). Intercom
functions will not work when both units are turned OFF.
3. Turn both pilot and co-pilot SDB units to the ON position. Turn the
squelch controls of both units to full clock-wise position. Set both
unit’s volume controls to mid position. Verify that all headset
positions can now intercom to each other, including the
passengers, if used.
4. Verify that with both SDB units ON, both pilots can independently
operate the aircraft radios. (Check that the pilot can transmit and
receive properly on the radios selected on the pilot’s audio panel.
Do a similar check on the co-pilot’s side.
5. Radio/Tower Transmit Check: If there is over-modulation
(garbled) or weak transmissions over the aircraft radio, an
appropriate adjustment can be made. There is a small, square,
adjustable trimmer potentiometer inside each of the two SDB units.
These adjust the mike outputs to the aircraft radios. It is accessible
through a hole in the side of each case and is marked “Mod. Adj.” It
can be adjusted with a screwdriver. Clockwise rotation increases
the output level to the aircraft radio mike 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 at a later
date. (The output is set for unity gain at Sigtronics). If adjustment is
necessary, it should be done one at a time. For example, first set
the pilot’s Mod. Adj. After the pilot’s side is set satisfactorily then
adjust the co-pilot’s unit.
This concludes the system check-out. Refer to the following
operating instructions for proper use and other operating modes of
the Sigtronics SDB-800 intercom system.
The Sigtronics’ SDB-800 is a voice actuated intercom for dual
audio buss’ aircraft with “transmit through the aircraft radio
capability” using your push-to-talk switches. Each intercom has
three controls.
Power Switch - Turns unit on and off and switches the pilot’s mike
direct to the radio in the “off” position.
Volume Control - Controls the intercom volume.
Squelch Control - Controls the threshold of amplifier turn-on. This
adjusts for variations in background noise found in different aircraft.
Each system will function as an independent intercom with pilot and
co-pilot having their own ON/OFF switch. When both intercoms are
ON, pilot, co-pilot, and 6 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
CAUTION - As is standard practice with all aircraft avionics
equipment, be sure that the aircraft radio master switch is OFF
when you start up the aircraft engine.
A. First set both SD13 ON/OFF switches to the “ON” position.
B. Turn both SDB unit volume controls to the 9 o’clock position and
both squelch controls all the way up (clockwise). Notice the
intercom is now continually activated and you should be able to talk
between headsets.
C. To adjust the intercom squelch controls for voice activated
operation (VOX), it is helpful to have some background noise
present. It may also be necessary to turn up the intercom volume
controls. Turn both 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 un ill 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.
D. Adjust the other intercom squelch control similarly by turning it
clockwise until you hear background noise. Rotate counter
clockwise incremental amounts until the background noise
Small adjustments may be necessary if aircraft background noise
changes significantly - such as from idle to maximum power.
Because of the dual intercom design of the SDB-800, transmit. ting
from both pilot and co-pilot positions is possible simultaneously and
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 mike is
routed through the intercom to the radio he selected. Only his mike
will be live. The microphone of any passengers connected to the
pilot’s side of the SDB-800 system will be muted when the pilot
transmits. Similarly, when the co-pilot transmits, only the co-pilot’s
mike 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. (A minor modification to the SDB
unit will enable it to simulate side-tone).
Radio monitoring is automatic. The radio monitor circuit is always
active; even with SD13 unit power switch OFF. Each pilot will only
hear the radio selected by his respective audio panel.
The intercoms may be turned off during solo flights. The pilot will
still hear the aircraft radio, since this circuit is always active, and
may transmit to ATC via his push-to-talk switch.
BACK-UP (Failsafe)
If a problem is suspected in the intercom, simply turn it off. You will
still receive the aircraft radio(s) as normal and will be able to
transmit from the pilot’s position. You may also use the hand mike,
however, the SDB unit should be turned off and you should unplug
your boom mike from the mike jack. (Leave headphone plugged in
for radio reception)
Form SDB-800-IS, Rev. A
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