PS Engineering PMA4000 Installation Manual - Manual (Page 8)

PS Engineering
PMA4000 Series Audio Selector Panel and Intercom System
Installation Manual
200-041-0002 Page 2-2 Rev 5, March 2007
2.3.4 Connector Assembly
The unit connectors are DB25 type. The unit has a male (bottom) a female (top), to pre-
vent incorrect connections. The top connector is generally the output, and the bottom
connector is generally the input connections.
These are crimp-type connectors. The AMP Contact Crimping Tool, AMP 601966-1 (or
MS22520 equiv.), with Positioning Tool 601966-5 must be used to ensure good quality
harness.
2.4 Cable Harness Wiring
Referring to Appendix C, assemble a wiring harness as required for the installation. All
wires must be MIL-SPEC in accordance with current regulations. Two- and three-
conductor with shield 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 the correct wire and techniques be used for proper
operation.
The shield should not be used as ground return. Terminate the shields with a short jumper
to the appropriate pin as shown in Appendix C, as close to the unit connector as practical.
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 PMA4000 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, particularly if the amplitude of noise is very high. There
must be at least 13 VDC present at the bottom connector, pin 13, of the PMA4000 for the
power supply to work in its designed regulation. Otherwise, it cannot adequately attenu-
ate 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 PMA4000s were designed in a RFI hardened chassis
and have internal Electromagnetic Interference (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 airframe that are detected by the audio system. Follow
the wiring diagram very carefully to help ensure a minimum of ground loop potential.
Use only Mil Spec shielded wires (MIL-C-27500, or better).
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.