Avionics News July 2019 - 37

of the last 40-plus years: two navs,
two comms, an ADF, a markerbeacon receiver, and a receiver for
both localizer and glideslope.
No benefit in having audio
on from all of these at once and
frequent benefit from silencing most
of them - but the mix will change,
often several times in the first and
last 15 minutes of a flight.
This situation calls for an audiocontrol panel capable of handling the switching needs of
all these radios - and even more, these days.
Without a device to control what audio source the
pilot, crew and passengers hear, the flight crew would
either be missing calls due to audio inundation or unable
to discern one source from another as various sources
stepped all over one another.
As a veteran of flying without both, going without
either tool falls far short of a welcoming thought.
Fortunately for today's aviators, the avionics industry
provides a wide range of options in both intercoms and
audio-control panels. Some integrate a marker-beacon
receiver, some don't. Others integrate an intercom
into the box - others do not. And still others integrate
an interface for connecting other audio sources to the
aircraft's audio system.
Without question, the industry offers an option suitable
for most applications.
Defining terms part I: intercom systems
An intercom is basically as the name implies: An
internal communications system linking occupants, in
this case of a cockpit or aircraft, so they can talk to and
hear others distinct from ambient aircraft-generated
noise. Intercom systems commonly used in light
general-aviation aircraft typically handle from two to 12
individual stations through individual headphones.
Prior to the invention of the aircraft intercom, lucky
flight crew communicated between duty stations via
voice tubes. Think of the sound-powered voice tubes of
late 19th century sailing vessels and you'll have an idea
of the technology.
When radios arrived in aircraft, the common electronic
speaker served as the common solution for bringing the
radio's audio into the aircraft cabin or cockpit.
Speakers for the cockpit radio gave way to aviation
headsets combining small speakers in earcups with a

microphone. The quality improved over the speakers if
for no other reason than the headset's audio was easier to
understand.
Today's headsets or headphones come in a dizzying
array of designs built around two basic versions: Ones
that use sound insulation to passively dampen the noise
reaching the ears of a wearer; and more-advanced
versions employing some form of active electronic
noise-canceling technology.
In essence, noise-canceling technology employs a
special microphone inside the headphones' ear cups to
detect background noise; a tiny computer processes that
ambient audio into a counter sound wave that "cancels"
the background sound, reducing the noise to nearly
imperceptible.
Some intercom systems are designed to perform best
in above-average noisy environments - such as opencockpit aircraft or tube-and-fabric fuselage aircraft in
which sound insulation isn't common.
Defining terms part II: audio-control panels
An audio-control panel basically consists of a box
housing circuitry for amplifying sound and the switching
functions to route a desired audio source - say the audio
from a VHF comm radio - to a cockpit speaker, a set of
headphones or some other device such as one of today's
smartphones.
The audio panel also controls the use of transmitters,
possibly even which headset and mic.
Multiple-radio panels existed before the invention of
the audio panel. But in those days, the switching mounted
scattershot style around the panel, typically close to the
device that switch controlled.
Audio-control panels range in capabilities from handling
two comm and two nav radios to ones capable of handling
20 or more audio sources and radios.
Continued on following page
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Avionics News July 2019

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