PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010
Page 2-9
Rev. 29, Sept. 2021
2.3.2
Cooling Requirements
Forced air cooling of the PAC24 is not required. However the unit should be kept away from heat produc-
ing sources (i.e. defrost or heater ducts, dropping resistors, heat producing avionics) without adequate cool-
ing air provided. Outside, ram air cooling of the unit is not permitted, and may result in damage.
2.3.3
Mounting Rack Installation
Remove the unit from the mounting tray by unscrewing the 3/32" hex-head screw that is between the RCV
and XMT legends. Use caution to avoid hitting the photo-detector lens. Carefully slide the unit free of the
tray. Set the unit aside in a safe location until needed. Install the tray using six clip nuts (475-630-0002),
and six FHP 6-32 x ½" screws (475-632-0012). The audio selector panel must be supported at front and
rear of the mounting tray.
2.3.4
Tray and Connector Assembly
The unit connector mates directly with the circuit board in the PAC24. The connector is a Molex crimp-
type, and requires the use of a Molex hand crimp tool, EDP P/N 11-01-0203, CR6115B (or equiv.). The
connector is mounted to the unit tray with #4-40 screws (475-440-0007), from the inside of the tray. Ensure
that proper strain relief and chafing precautions are made during wiring and installation, using the cable
clamp (625-001-0002). Secure the ground bar (430-630-0002), if desired using, #6-32 nuts (475-632-0003)
and #6-32 lock nuts (475-632-0004).
2.4
Cable Harness Wiring
Referring to the appropriate Appendix, assemble a wiring harness as required for the installation. All wires
must be MIL-SPEC in accordance with current regulations. Two- and three-conductor shielded wire must
be used where indicated, and be MIL-C-27500 or equivalent specification. Proper stripping, shielding and
soldering technique must be used at all times. It is imperative that correct wire be used.
Refer to FAA Advisory Circular 43.13-2A for more information. Failure to use correct techniques may
result in improper operation, electrical noise or unit failure. Damage caused by improper installation will
void the PS Engineering warranty.
2.4.1
Noise
Due to the variety and the high power of radio equipment often found in today's general aviation aircraft,
there is a potential for both radiated and conducted noise interference.
The PAC24 power supply is specifically designed to reduce conducted electrical noise on the aircraft power
bus by at least 50dB. Although this is a large amount of attenuation, it may not eliminate all noise, particu-
larly if the amplitude of noise is very high. There must be at least 13.8 VDC present at the bottom connect-
or, pin 25, of the PAC24 for the power supply to work in its designed regulation. Otherwise, it cannot ade-
quately attenuate power line noise. Shielding can reduce or prevent radiated noise (i.e., beacon, electric
gyros, switching power supplies, etc.) However, installation combinations can occur where interference is
possible. The PAC24 was designed in a RFI hardened chassis and has internal Electromagnetic Interfer-
ence (EMI) filters on all inputs and outputs.
Ground loop noise occurs when there are two or more ground paths for the same signal (i.e., airframe and
ground return wire). Large cyclic loads such as strobes, inverters, etc., can inject noise signals onto the air-
frame that are detected by the audio system. Follow the wiring diagram very carefully to help ensure a min-
imum of ground loop potential. Use only Mil Spec shielded wires (MIL-C-275000, or better).Under no
circumstances combine a microphone and headphone wiring into the same shielded bundle. Always use a
2- or 3-conductor, shield wire as shown on the installation wiring diagram.
Radiated signals can be a factor when low level microphone signals are "bundled" with current carrying
power wires. Keep these cables physically separated. It is very important that you use insulated washers to
isolate the ground return path from the airframe to
all
headphone and microphone jacks.
Adding a high-performance audio control system, particularly in conjunction with high-performance active
noise canceling headsets, cannot improve on older avionics that were designed for cabin-speaker use. PS