PS Engineering PMA7000M-S Installation Manual - Manual (Page 11)

PS Engineering
PMA7000M-S Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-070-0012 Page 2-4 Rev. 12, Sept. 2000
2.4.4 Power
The PMA7000M-S-Series are compatible with both 14 and 28 Volt DC systems. A two (2) Amp circuit
breaker is required for 14 VDC installations, and a three (3) Amp breaker for 28 VDC aircraft. Power and
ground wires must be a twisted #18 AWG pair. Connect airframe power ground to J1 (bottom connector)
Pin Z only. No dropping resistors are required.
2.4.5 Communications Push-to-Talk
An important part of the installation is the PTT (Push-To-Talk) switches that allow the use of your aircraft
communications radio for transmissions. There are three typical configurations that can be used. Select the
case that best fits the installation. Only the person who presses their PTT switch will be heard over the ra-
dio. If the pilot and copilot both use the PTT, the only pilot position has access to the radio. The pilot posi-
tion will have PTT control regardless of the mic selector switch or copilot PTT when the PMA7000M-S is
in the
OFF /E MG mode.
CASE I: PTT is built into both pilot and copilot yokes.
CASE II: PTT is in pilot yoke only. This configuration requires a modified external PTT switch plugged
into the copilot's microphone jack. (See Appendix A). When the copilot's PTT is pressed, the intercom
switches the microphone audio from pilot to copilot mic.
CASE III: No built in PTT. This requires two built in PTTs to be installed, or modified external PTT
switches to be used. Modify external PTT as required. See Appendix A.
2.4.6 Audio Panel interface
The PMA7000M-S is designed to interface with standard aircraft avionics, and presents a 500
Ω
receiver
impedance. 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 con-
ductor of the twisted-shielded cable.
2.4.6.1 Speaker Load
The PMA7000-series contains a speaker amplifier. Some units with internal speaker amplifiers, such as the
King Radio KX170-series, require a resistive load to prevent damage if their speaker amplifier is not used.
Connect the speaker output from the unit to the load input on the PMA7000M-S (J1, pins 19 and L, 16 and
M. The speaker load in 16
Ω
, 3W.
2.4.7 Com 3 Audio
As installed in the standard configuration, the PMA7000M-S Com 3 audio is placed in the audio when the
mic selector switch is in the Com 3 position (fully CCW). Pushing the receiver selector buttons can monitor
Com 1 and Com 2 audio. If monitoring of Com 3 is desired in the Com 1 or Com 2, connect Com 3 audio in
parallel to the AUX input (J1, pin 11).
2.4.8 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.
2.4.9 "Swap" Mode
When a momentary, normally open, push-button switch is connected between pin 10 on the top connector
and aircraft ground, the user can switch between Com 1 and 2 by depressing this switch without having to
turn the mic selector switch. This yoke-mounted switch eliminates the need to remove your hands from the
yoke to change transceivers.