Audio Amplifier/Intercom/Marker Beacon Receiver
pilot's PTT is activated, his voice is heard over the speaker. The copilot can continue to
use the selected com.
We recommend installing a toggle switch to connect the cabin speaker output (pin W,
bottom connector) to a rear or public address speaker instead of the cockpit speaker close
to the pilot. This will prevent feedback.
2.4.13 PA Mute (J1, Pin 18)
Pin 18 of J1 is a TTL logic output that is pulled low during PTT operation. This serves as
an input to external public address system to prevent feedback during transmissions.
2.4.14 Control Output (J2, Pin A)
Pin A of the top connector is pulled to ground whenever the AUX button is depressed.
This serves as a control line for external devices, such as a entertainment system that the
pilot wishes to control.
2.4.15 VOX Override (J2, Pin U)
Connecting pin U of the KMA 28 of J2 to ground will force the IntelliVox® open. This
can be hooked up as a hot mic switch which will place all microphones on the intercom.
This can also be connected through a momentary switch to serve as a VOX test switch, if
desired. Because the IntelliVox® will close in the presence of a steady tone, this pin is
used in testing to defeat the IntelliVox® software.
The marker beacon receiver is included in the KMA 28.
2.5.1 Middle Marker Sense
A Middle Marker sense output signal is available from the KMA28 to flight control sys-
tems. This function will not operate during the test mode. This output will go to +4.7
VDC ( 0.5 VDC) when a valid Middle Marker signal is received. This output is J1, pin
2.5.2 External Marker Lights
For installations that require external marker beacon lights, there are three outputs that
can drive 12-Volt lamps only. The external output lamps are driven high (+9 VDC 1.5
VDC) when active. Maximum source current per lamp is 125 mA. Voltage varies with
2.5.3 Marker Antenna Installation
Refer to aircraft and antenna manufacturer's installation instructions, as well as AC43.13-
2A (or later revision), Chapter 3, for information on proper antenna installation tech-
niques. The marker beacon antenna must be mounted on the bottom of the aircraft.
Rev. 0, Sept. 2000