Sigtronics RMS-640 Operating Instructions

Sigtronics ST-440 / ST-640 STEREOCOM Operating Instructions

INTERCOM OPERATION

The intercom portion of the Sigtronics Stereocom ST440
/ ST-640 system is voice actuated (VOX) with “transmit
through the aircraft radio capability” using your push-to-talk
switches. Three controls are provided on the SAS units:

OFF/ALL/ISO Switch - Sets the intercom mode of
operation.

VOL - Volume Control - Controls the intercom volume. (Does
not affect aircraft radio volume. Set radio volume on radio
as normal).

SQ - Squelch Button - Automatically sets the VOX operation
of the intercom for variations in background noise levels and
differences in headset microphones.

Intercom operation and adjustment can be performed by
the following procedure:

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.

1. With aircraft power on, set both the PILOT and PASS.
MUSIC ON/OFF switches to “OFF”.

2. Set the SAS OFF/ALL/ISO switch to the “ALL” position - the
preferred mode for setting the squelch. The SAS squelch
level can also be set with the SAS in the “ISO” mode, but
the pilot headset audio will not be utilized for squelch level
setting. For best system performance set the intercom
VOLume control as low as possible. On most systems this
will be approximately between 1/4 to 1/3 open. Note:
the intercom volume control only adjusts the volume of
conversation between the headsets inside the aircraft. It
does not affect the level at which you hear the aircraft
radio(s) or the level of the music. Notice the intercom is
now continually activated (hot mic mode) and you should
be able to talk between headsets.

3. To adjust the intercom squelch control for voice activated
operation (VOX), press and hold the “SQ” button down.
Now announce to the other persons in the aircraft not
to talk because you need a moment to set the intercom.
When all are silent release the “SQ” button. The intercom
will immediately go quiet. In approximately one second

the intercom will briey pop on. This tells you the squelch
has nished automatically setting. If someone did speak
while the intercom was setting, it will have to be set again.
This is because the intercom would have tried to set to
a level just above the persons voice level instead of just
above the aircraft background noise level.

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.

In most aircraft, the squelch level wont need to be set again
until the next ight. In some high noise aircraft it is better to
set the squelch during climb or cruise.

Hot Mic Mode

When the SAS intercom turns on, it automatically comes
up in “hot mic” mode (non voice activated mode). During
a ight, if you want to deactivate the voice activated mode
and return to hot mic mode, simply turn the OFF/ALL/ISO
switch to “OFF” and wait 3 seconds and then turn it back to
“ALL” or “ISO”. To facilitate automatic setting of the squelch
level, whenever the “SO” button is held down, the intercom
also goes into hot mic mode.

Radio Transmit Mode

When the SAS is in the “ALL” mode, transmitting from both
pilot and co-pilot positions is possible on a one -at-a-time
basis. As normal, the pilot selects the appropriate radio he
wishes to use. When the pilot presses his PTT switch, his
headset mic is automatically routed through the intercom
to the radio. Only his mic will be live. The microphones of
the co- pilot and any passengers, will be muted when the
pilot transmits. Similarly in the “ALL” mode, when the co­pilot transmits, only the co-pilots mic will go out on the
radio. When transmitting, the pilots will hear their own
voice via the aircraft radio sidetone return. (If the radio
does not provide transmit sidetone, then you will not
hear your voice. A minor modication to the SAS unit will
enable it to simulate sidetone. (See “SAS - 440 / SAS-640
Sidetone Modication” section under the “HELPFUL HINTS
AND TECHNICAL INFORMATION” in the ST-440 / ST-640
STEREOCOM INSTALLATION INSTRUCTIONS). When the

Specialists in “SOUND” Management

178 East Arrow Highway, San Dimas, CA 91773 ( 909 ) 305-9399

SAS is set to the “ISO” mode, only the pilot can transmit
and receive on the aircraft radio(s). The pilot will not hear
intercom and cannot talk to the other headsets. The co­pilot and passengers still have intercom, but do not hear
the radios.

Solo Flights

Since the intercom is not needed during solo ights, it may
be turned “OFF”. The pilot will still hear the aircraft radio(s),
since this circuit is always active, and may transmit to ATC
via his headset and push-to-talk switch. The pilot can also
listen to music (interrupted only by aircraft radio trafc) by
turning “ON” the PILOT MUSIC ON/OFF switch.

The Pilot is automatically switched from the music source
to the aircraft VHF radio when a radio message is received
or transmitted and is switched back when the radio trafc
is completed. His music is also automatically switched out
while someone is talking on the intercom (in “ALL” mode
only).

The Co-pilot and passengers music is interrupted by the
intercom. If the SAS is in the “ALL” mode the Co-pilot and
Passenger music is also interrupted by the aircraft radio(s).
In order to eliminate VHF interrupt, it is necessary to turn
the VHF radio volume down or off.

Stereo Headsets

Fail-Safe

If power to the SAS unit fails, the pilot can still transmit and
receive on the a/c radio(s) (assuming the radio(s) are still
functioning). Additionally, if a problem is ever suspected in
the intercom, simply turn it to “OFF”. In this mode you will
also be able to transmit and receive on the aircraft radio(s)
from the pilot’s position. The hand mic may also be used,
however, the SAS unit should be turned to “OFF” and you
should unplug your headset mic plug from the mic jack.
(Leave headphone plug in for radio reception).

MUSIC SWITCHER OPERATION

Switcher Panel Controls:

PILOT MUSIC ON/OFF Switch - Turns Pilots music switcher
on or off.

PASSenger MUSIC ON/OFF Switch - Turns Co-pilot and
Passengers music switcher on or off.

To operate, turn “ON” the appropriate MUSIC ON/OFF
switch(s). Connect your music source to the music input
jack, if applicable. Turn your stereo music source on and
adjust to suitable listening level.

Sigtronics stereo headsets are specically designed for the
aircraft high noise environment and give excellent noise
attenuation. They also provide full frequency response
stereo for maximum enjoyment. They are compatible with
aircraft mic circuits and can be used as general aviation
headsets in aircraft that are not equipped with stereo
headphone jacks. This is because they include a switch
to change from “Stereo” to “Monaural.” No adapters
required.

NOTE: General aviation headset (monaural) phone plugs
should not be plugged into Stereocom stereo phone jacks.
A monaural plug in a stereo jack shorts out one of the audio
channels and therefore renders the aircraft VHF radio and
intercom reception inoperative. (You may still hear music,
however). General aviation headsets may be used only if
one of the following three changes are made:

1. Monaural to stereo adapters are used on the headset
headphone plugs. (Only monaural music will be
heard.)

2. The general aviation headsets are re-wired for stereo
reception.

3. Install the Sigtronics Stereocom system for
monaural operation. See Note 9 under the “WIRING
INSTRUCTIONS” section of the ST- 400 / ST- 600
STEREOCOM INSTALLATION INSTRUCTIONS.

Sigtronics Corporation

178 East Arrow Highway
San Dimas, CA 91773
Phone: [phone]
E-mail: [e-mail]
Web Site: www.sigtronics.com

1-12-2007 ST440OPR.PDF