PS Engineering
PMA7000B Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-780-0004 Page 2-4 Feb. 2004
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 PMA7000B is in
the
OFF/EMG 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 PMA7000B is designed to interface with standard aircraft avionics, and presents a 500Ω receiver im-
pedance. 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.
2.4.6.1 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 PMA7000B (J1, pins 19 and L, 16
and M. The speaker load is 16 Ω, 3W.
2.4.7 Com 3 Duplex (TEL) Function for Cell Phones
As installed in the standard configuration, the PMA7000B Com 3 function operates conventionally. Push-
ing the Com 3 Xmt button places the receive audio from Com 3 in the headset and applies the pilot or copi-
lot microphone to the Com 3 when the appropriate PTT is activated.
If J2, Pin J is connected to aircraft ground, the PMA7000B is forced into Com 3-Duplex mode. This mode
is designed to operate with telecommunications systems, such as the AirCell Guardian 1000. Audio streams
selected by hook switches are provided to the COM 3 output, the PTT for Com 3 is inactive, and audio
from Com 3 is presented to the headset. This allows a telephone-like audio interface. The COM 3 input and
output are compatible with aviation radios.
When Pin J is grounded, the PMA7000B is also compatible with many cellular telephones with hands-free
headset interfaces. A 1/8” or 3/32” jack can be installed on the aircraft panel, and interfaces with the
PMA7000B as shown: A patch cord (3/32” to 3/32”) is available from PS Engineering under P/N 425-006-
7026.
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