KING
KMA 20/KR 21
MARKER BEACON RECEIVER/
ISOLATION AMPLIFIER
SECTION
I
GENERAL
INFORMATION
1.1 INTRODUCTION
The King KMA 20 is a compact transistorized unit providing the functions of marker
beacon receiver, isolation amplifier and audio control panel. The unit has been styled
to harmonize with the all new generation of Silver Crown panel mounted equipment.
TSO certification of the KMA 20 assures operation under varying environmental
conditions.
The KMA 20 is designed to provide auniformly functioning aircraft radio system when
utilized with other units of the new Silver Crown line. Although the equipment is designed
primarily for use with the KX 170 NAV/COMM unit, it will also perform effeciently with
older Silver Crown transceivers and radios.
Significant new features of the KMA 20 design include its AUTO switch feature: semi-
concealed marker light presentation and its ability to control COMM and NAV audio
independently. Automatic dimming circuitry for the marker lamps, to compensate for
ambient cockpit lighting, is also incorporated in the design.
Within the KMA 20, the marker beacon receiver comprises one section of the unit.
The marker receiver of the KMA 20, available without the isolation amplifier and audio
panel is the KR 21. The receiver is a crystal controlled superheterodyne receiver and
has excellent selectivity and freedom from interference of television and FM stations.
Operating controls for the marker receiver consists of two toggle switches on the KMA
20: a HI-LO sensitivity and lamp test control and an audio selector switch. The KR 21
has only the HI-LO sensitivity and lamp test control. A three light presentation is de
signed into the front panel of the unit with colored lenses to indicate passage over the
markers. Besides the colors, the stations are identified by the letters A-O-M engraved
on the lenses plus the appropriate frequency audio tone. Should the aircraft user desire a
aremote location for the marker lights, King Radio Corporation manufacturers an
optional remote light assembly designated the KA 40 for use with the KMA 20 only.
The isolation amplifier of the KMA 20 makes possible the combining of all receiver
audio inputs into a single cockpit speaker with 40db of isolation between each radio. The
input power levels of the signals are amplified to the level necessary to drive a 4 ohm
speaker. An electronic muting circuit (diode switch) is provided to automatically isolate
the output of all receivers from the isolation amplifier whenever the microphone button
Rev. 1, August, 1972 Page 1-1
