PS Engineering PAC24 Installation Manual - Manual (Page 17)

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page 2-10 Rev. 24, Dec. 2013
2.4.5 Audio Panel interface
The PAC24 is designed to interface with standard aircraft avionics, and presents a 500 receiver imped-
ance. For best results, a twisted-shielded cable is recommended from the avionics audio source to the au-
dio panel, with the shield grounded at the audio panel end.
Some avionics do not provide a separate audio low, and may introduce additional electrical noise into the
system. For best results, connect the audio low from the audio panel to the radio ground, using one con-
ductor of the twisted-shielded cable.
2.4.6 Transmit Interlock
Some communications transceivers use a transmit-interlock system. To fully utilize the Split Mode fea-
ture, this function must be disabled. Consult that manufacturer's installation manual.
2.4.7 "Swap" Mode
When a momentary, normally open, push-button switch is connected between pin U (14 V) or 18 (28V
lighting) on the unit connector and aircraft ground, the user can switch from Com 1 to 2 to 3 etc. by de-
pressing this switch without having to change the mic selection. This yoke-mounted switch eliminates the
need to remove your hands from the controls to change transceivers.
NOTE: Swap mode is active if the proper DIP switch selection is made internally to the unit.
2.4.8 Backlighting
The PAC24 has an automatic dimming of the pushbutton annunciator LEDs and marker lamps controlled
by a photocell. Control of the unit backlighting is through the aircraft avionics dimmer. Connect the dim-
mer control line to J3 pin 18 for 14-volt systems, and to J3 pin U for 28-volt systems. Pin 17 is light
ground.
If an external dimmer control is not used, a constant low-level back light illumination can be established
for nighttime viewing. Pin 18 or U (depending on system voltage) must be tied to power (J3, pin 25) for
the back lighting system to work. The photocell mounted in the unit face will automatically adjust the
intensity of the push-button annunciator LEDs.
2.4.9 Unswitched inputs
J3, pin 10 is the unswitched input number 1 and J3 pin 14 is unswitched input 2. These inputs are pre-
sented to the pilot and copilot regardless of the audio configuration, and will always mute the entertain-
ment inputs. These 510Ω inputs can be used for altimeter DH audio, GPS waypoint audio, autopilot dis-
connect tones, or any other critical audio signal.
NOTE: In installations where an expansion unit is NOT used, the passenger and copilot audio output is
paralleled (J1, pin b). Therefore, unswitched audio will be heard by the passenger(s). Use an expansion
unit, P/N 11616, or 11616R (remote) to isolate passenger audio from unswitched alert audio.
2.4.10 PA Mute (J3, Pin 8)
Pin 18 of J3 is a TTL logic output that is pulled low during PTT operation. This serves as an input to ex-
ternal public address system to prevent feedback during transmissions.
2.4.11 Public Address (J3, Pin B)
When the Speaker mode switch is in the PA mode, and the pilot’s PTT is activated, his voice is heard over
the PA speaker output on J3, Pin B. The copilot can continue to use the selected com.
In a dual installation, both the pilot and copilot panels can be connected to separate PA Speakers, for in-
stance, one ramp hailer, and one public address speaker.
NOTE: Connecting two audio panels to a single speaker for cockpit and/or cabin address can
result in damage to the audio panel.