PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0008 Page 2-7 Rev. 8, June 2003
2.4.2.2 Dual KMA24H -71 Installation
In a dual KMA24H-71 installation, we recommend that the ISO/Normal/Private switches be removed.
These switches apply a ground to logic inside the KMA24H.
THE CONNECTIONS BETWEEN THE AUDIO PANELS MUST BE LEFT INTACT
. This includes Pins
V to V (Key Enable), 21 to 24 (Isolate /Isolate 22) and Y to Y (Private). PS Engineering uses these lines
for data bus communications between panels.
2.4.3 Power
The PAC24-Series are compatible with both 14 and 28 Volt DC systems. A three (3) Amp breaker is re-
quired. Power and ground wires must be a twisted
#18 AWG pair. Connect airframe power ground to J3
Pin 25 only. No dropping resistors are required.
2.4.4 Communications Push-to-Talk (single panel installation)
Unless the system is in split mode, only the person who presses their transmit PTT switch will be heard
over the radio. If the pilot and copilot both use the PTT, only the pilot position has access to the radio. The
pilot position will have PTT control regardless of the mic selector switch or copilot PTT when the PAC24
is in the
OFF/EMG mode.
2.4.4.1 Communications Push-to-Talk (Dual Panel Installation)
The PAC24 automatically senses if the other audio panel is transmitting. If communications transceivers
selected for transmit are different (Com 1 pilot, Com 3 copilot), both panels will allow simultaneous, dual
transmission (split mode). If the same radio has been selected for transmit on both audio panels, the pilot
mic will have priority, and the copilot will not transmit.
2.4.5 Audio Panel interface
The PAC24 is designed to interface with standard aircraft avionics, and presents a 500Ω receiver imped-
ance. For best results, a twisted-shielded cable is recommended from the avionics audio source to the audio
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 conduc-
tor of the twisted-shielded cable.
2.4.6 Transmit Interlock
Some communications transceivers use a transmit-interlock system. To fully utilize the Split Mode feature,
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 turn the mic selector switch. 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
(41 pages)
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