PS Engineering PM3000 Installation Manual - Manual (Page 4)

Page 4 200-193-0005 Rev. 8, Nov. 2013
into the aircraft and connect them directly to the ap-
propriate pins of the PM3000. See the wiring diagram
for all details of the wire harness interconnect.
2.4.1 Electrical Noise Issues
WARNING: You must use individual shielded cables
for the microphone and headphone jacks. Combining
these two wires WILL cause loud oscillations and de-
grade the intercom function. The oscillation is caused
by the cross-coupling between the large headphone
signal and the small microphone signal. The resulting
feedback is a high-pitched squeal that varies with the
volume control.
Due to the variety of the radio equipment found in
today's general aviation aircraft, there is the potential
for both radiated and conducted noise interference.
The PM3000 has a specially designed power supply to
reduce conducted electrical noise on the power bus of
the aircraft by at least 50dB. Although this is a very
large amount of attenuation, it does not eliminate all
noise when the amount is excessive. There must be at
least 13.75 Volts DC present at the PM3000 for the
power supply to work within its optimum regulation.
Otherwise, it will not be able to attenuate noise prop-
erly.
Shielding can protect the system from radiated noise
(rotating beacon, electric gyros, switching power sup-
plies, etc.). However, installation combinations can
occur where minor interference is possible. The
PM3000 was designed in an interference -protected
chassis and has internal filter capacitors on all input
lines.
Ground loop noise occurs when there are two different
return paths for the same signal, such as airframe and
ground return wire. Large cyclic loads such as strobes,
inverters, etc., can inject audible signals onto the air-
frame return path. Follow the wiring diagram very
carefully to help insure a minimum of ground loop
potential. Radiated signals can be a factor when low
level microphone signals are bundled with current car-
rying power wires. Keep these cables separated.
Insulating washers are required on all microphone and
headphone jacks to isolate them from aircraft ground.
The use of a conductor instead of a shield for ground
return eliminates these ground loop paths.
2.4.2 Power & Dimmer
The PM3000 was designed to work with 12.8 to 27.5
volt DC negative ground systems. The PM3000 must
be externally protected with a one ampere (1A) circuit
breaker or fuse.
[11931A & 11933A] Connect Pin 5 to the aircraft
dimmer bus. This will adjust the Power/Xmit LED for
varying lighting conditions. If no connection is made,
the LED will be at maximum brightness.
The unit is shipped for 14 VDC dimmer systems. For a
28 VDC aircraft dimmer system, open the PM3000
case and remove the Jumper J2.
2.4.3 Unswitched Audio Input
The PM3000, P/N 11931A & 11933A have two
unswitched audio inputs available for 500Ω aviation
audio sources. Pin 17 is Unswitched #1, and is also
provided to the pilot in Fail-Safe Mode. Unswitched
#2 input is Pin 4.
2.4.4 Sidetone
The PM3000 can be modified to produce sidetone
(hearing your voice during transmit), if the aircraft
radios do not produce it. Contact the PS Engineering
factory for details.
2.4.5 Entertainment Input
Stereo entertainment devices can be connected to the
PM3000. Install ⅛" stereo jacks convenient the pilot
and passengers to connect the entertainment devices
into the system. PM3000, part number 11931A has a
single entertainment input. The part number 11932
will accommodate two inputs, one for the crew, and
another separate input that feeds the 4 passengers in
CREW mode.
It is possible to use only one entertainment device to
provide music for both inputs in the 11932 system by
connecting the output of the entertainment device in
parallel to both the Music #1 and Music #2 inputs. We
highly recommend, however, that you install a switch
between the entertainment device and Music #1. This
will give the pilot and copilot the ability to switch off
music while in the CREW mode.
The music device will automatically mute when the
ICS or aircraft radio becomes active. The Soft Mute™
feature slowly returns the music to full volume when
the activity ceases. Pressing the Mute disable switch
Use only low level output of the entertainment devices
to connect to the PM3000. Maximum signal level on
the input is 2-volts peak-to-peak.
DO NOT USE SPEAKER
OUTPUT LEVELS.
This will cause internal damage.
If speaker levels are to be used, install an
Audio Link, p/n 101PL2,
available from Crutchfield (1-800-955-3000).