Avionics News October 2022 - 54

Advertisers Index
Aero Standard . . . . . . . . . . . . . . . . . . . . 70
Aircraft Electronics Association . . . IBC, 69
Aircraft Lighting International . . . . . . . . 31
Aircraft Spruce . . . . . . . . . . . . . . . . . . . . 5
Avidyne . . . . . . . . . . . . . . . . . . . . . . . . . 45
Avionics News . . . . . . . . . . . . . . . . . . . 63
AVweb . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Becker Avionics . . . . . . . . . . . . . . . . . . 58
Cal Labs . . . . . . . . . . . . . . . . . . . . . . . . 70
CiES . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Corporate Angel Network . . . . . . . . . . . 71
Dallas Avionics . . . . . . Inside Front Cover
Daniels Manufacturing Corp . . . . . . . . . 62
Duncan Aviation . . . . . . . . . . . . . . . . . . 41
EDMO . . . . . . . . . . . . . . . . . . .Back Cover
Elliott Aviation . . . . . . . . . . . . . . . . . . . . 55
Garmin . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Gogo Business Aviation . . . . . . . . . . . . 59
KGS Electronics . . . . . . . . . . . . . . . . . . 51
Pacific Southwest Instruments . . . . . . . 37
PIC Wire & Cable . . . . . . . . . . . . . . . . . 26
Precision Aviation Group . . . . . . . . . . . . 33
Sandia Aerospace . . . . . . . . . . . . . . . . . 44
Schweiss Doors . . . . . . . . . . . . . . . . . . 70
SmartSky Networks . . . . . . . . . . . . . . . 15
Tech-Aid Products . . . . . . . . . . . . . . . . . 70
TGH Aviation . . . . . . . . . . . . . . . . . . . . . . 7
Tri-Star Technologies . . . . . . . . . . . . . . 27
True Blue Power . . . . . . . . . . . . . . . . . . . 1
uAvionix . . . . . . . . . . . . . . . . . . . . . . . . 36
WBParts Express . . . . . . . . . . . . . . . . . 25
54 avionics news * october 2022
THEORY & PRACTICE
Continued from page 53
What we see in Figure 1A are a carrier and sidebands. Sidebands are
the sum and difference signals. If we change the modulation frequency,
the location of the sidebands will change. Figure 1B shows the WWV
signal while the station was transmitting an 800 Hz tone. Figure 2 shows
the spectrum analysis of a local AM radio station on 1340 kHz; the radio
announcers were talking. There are many frequencies included in the
human voice, and as you might imagine, the sidebands were changing
frequency rapidly enough, and the analyzer could not separate the signals.
The general rule for AM and for any type of modulation is more
data requires more bandwidth. A simple tone requires little bandwidth,
whereas voice requires more.
For long-distance communication, narrow bandwidth signals work
better than wide bandwidth signals. A form of modulation related to
AM is Single Side Band, or SSB. For more efficiency, and for ease of
long-distance communication, where the radio signal refracts through
the ionosphere, we can use SSB. In this case, the carrier and one of the
sidebands is filtered out before being transmitted. More exactly, the
signal can be referred to as SSB Suppressed Carrier, or SSBSC. For a
radio listener using AM, the SSB signal is impossible to understand. A
radio designed for SSB will have circuitry within, which will recreate
the missing carrier and the other sideband. If the lower sideband is
filtered out, we call the signal an Upper Side Band signal, or USB,
which is used in aviation. If the upper side band is filtered out, we call
the signal a Lower Side Band Signal, or LSB.
Since modulation is the fancy word for change, frequency modulation
is self-explanatory. In this case, we change frequency to send
information. Nearly all public service and business communications
that have not switched to digital use frequency modulation, as does FM
broadcast stations.
Logic
Logic
Logic
High Frequency Filter
Logic
Low Frequency Filter
Logic
Figure 4: A digital FSK signal shown, with one method of determining zeros and ones. This
image is a modified version of a figure shown in the textbook, Avionics: Beyond the AET.
Avionics News October 2022

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