Radionavigation ATPL Key Notes

RADIO
NAVIGATION
1
–
BASIC
RADIO
PRINCIPLES


BASIC
TERMS
PHASE
DIFFERENCE
MODULATION
TYPE
1
-­‐
KEYING





• Radio
waves
travel
at
the
speed
of
light:
• Can
only
be
measured
when
the
signals
have
• Interrupting
the
carrier
wave
to
give
morse

o c
=
3
x
108
m/sec
the
same
frequency
(or
wavelength).
code.


• Will
temporarily
interrupt
the
nav
aid

• Frequency
(f)
–
Number
of
complete
cycles
output
in
order
to
tx
the
morse
code.

per
second.
Measured
in
Hertz
(Hz)

POLARISATION

o 1
cycle
per
second
=
1
Hz



o 1
kHz
=
103
Hz
MODULATION
TYPE
2
-­‐
AM

• The
electrical
and
magnetic
components
of
a

o 1
MHz
=
106
Hz


radio
wave
travel
at
right
angle
to
each

o 1
GHz
=
109
Hz
• AM
=
Amplitude
Modulation

other
and
in
the
direction
of
propagation.


• Amplitude
of
the
carrier
wave
is
varied
in

• Plane
of
electrical
component
=
plane
of

• Wavelength
(𝜆)
–
Distance
travelled
in
one
accordance
with
the
audio
signal
amplitude.

polarisation.

complete
cycle.
Measured
in
metres.
• Carrier
wave
frequency
is
kept
constant.

• Transmission
from
vertical
aerial
gives
a


• Oldest
method
apart
from
keying.

vertical
electric
component
and
horizontal

• Time
period
(𝑻)
–
Time
taken
to
complete
• Small
amplitude
areas
give
a
weak
signal

magnetic
component.

once
cycle.
T
=
1
/
f
that
is
prone
to
interference
(especially

• Transmission
from
horizontal
aerial
gives


since
it
operates
in
low
frequency
spectrum)

horizontal
electrical
component
and
vertical

• 𝑪 =  𝝀  ×  𝒇
• Modulation
circuit
requires
extra
power
to

magnetic
component.


vary
the
amplitude.

• In
circular
propagation,
both
components

• Low
Frequency
=
Long
Wavelength


spin
about
the
axis
of
advance.

• High
Frequency
=
Short
Wavelength




POLAR
DIAGRAMS

ANTENNA
LENGTH



1.
Omnidirectional

• Ideal
antenna
length
is
½
the
wavelength.
2.
Directional
(Inc
unwanted
side
lobes)

• If
not
possible,
then
1/4
,
1/8
etc
will
do.
• Applies
to
both
Tx
and
Rx
aerials.



MODULATION



• Modulation
adds
information
to
an

otherwise
empty
carrier
wave.


, RADIO
NAVIGATION
1
–
BASIC
RADIO
PRINCIPLES



MODULATION
TYPE
3
-­‐
FM
MODULATION
TYPE
4
-­‐
PULSE
FREQUENCY
SPECTRUM





• FM
=
Frequency
Modulation
• Radio
wave
is
switched
on
and
off
at
regular
• Frequency
range
repeats
(kHz
/
MHz
/
GHz)

• Frequency
of
the
carrier
wave
is
varied
in
intervals,
effectively
forming
pulses
of
radio
o 3
–
30

accordance
with
the
audio
signal
amplitude.
energy.
o 30
–
300

• Carrier
wave
amplitude
is
kept
constant.
• Use
in
radar.
o 300
-­‐
3000

• A
+ve
amplitude
=
higher
frequency
• Transmits
0’s
and
1’s
effectively.


• A
–ve
amplitude
=
lower
frequency
• Wave-­‐length
can
be
derived
with
𝐶 =  𝜆  ×  𝑓




• FM
TX’s
are
simpler
and
cheaper
than
AM
AM
SIDEBANDS


• Lower
modulation
power
required


• Constant
amplitude
=
stronger
• Whenever
a
carrier
is
AM
modulated
by
a

• VHF
operation
=
almost
static
free
frequency
lower
than
itself,
sidebands
are

• Horizontally
polarised
so
suffers
less
from
created.

weather
induced
static
(vertically
polarised)
• Carrier
Wave
=
500
kHz,
Audio
Freq
=
4
kHz


o 4
kHz
is
filtered
out.

• Receivers
are
more
complex.
o 496
kHz
/
500
kHz
/
504
kHz
output

• Wider
frequency
band
required.
• Passband
is
a
filter
used
to
get
rid
of


unwanted
frequencies
so
bandwidth
can
be


reduced.


• Single
Sideband
(SSB)
–
Often
only
1
of
the

outputs
is
TX’d.
The
sideband
carries
the

information
rather
than
the
carrier.

o With
all
TX
power
focused
on
one

sideband,
range
is
increased.
EMMISSION
CODES

• FM
has
many
more
sidebands
than
AM.


• 1st
=
Type
of
modulation

• 2nd
=
Nature
of
modulating
signal

HF
COMMS
&
HF
VOLMET
• 3rd
=
Type
of
information
transmitted



• Use
single
sideband

• HF
SSB
=
J3E


, RADIO
NAVIGATION
1
–
BASIC
RADIO
PRINCIPLES



REFRACTION
SURFACE
ATTENUATION
ATTENUATION
&
REFRACTION
BY
FREQ





• Radio
waves
are
refracted
when
travelling
• As
a
radio
wave
passes
over
a
surface
it
• Top
Column
=
A
-­‐
RADAR

obliquely
from
a
medium
of
one
density
loses
energy.


to
another
of
different
density.
• Higher
frequencies
are
more
susceptible
as

• Due
to
different
velocities
there
is
a
slight
they
hit
the
surface
more
often.

change
of
wavelength.

• Low
to
high
density
=
slows
down
and

bends
towards
the
normal.
IONOSPHERIC
ATTENUATION




• Types
of
refraction:
• The
ionosphere
and
particles
in
the

o Coastal

(Land
to
sea.
Flying
higher
or
atmosphere
can
absorb
and
block
a
radio

moving
beacon
towards
coast
will
wave.

reduce
effects)

o Atmospheric
(Density
change
with

altitude.

ATMOSOHERIC
/
RADAR
ATTENUATION

o Ionospheric



• When
radar
energy
strikes
water

BASIC
RADIO
CIRCUIT

droplets,
some
energy
is
absorbed
(and



attenuated)
and
some
is
reflected.

REFLECTION
• Human
Ear:
20
Hz
–
20
kHz



• Radio
waves
bounce
off
a
solid
surface.
DOPPLER
EFFECT

• If
two
signals
arrive
at
the
same
time
but
out


of
phase,
there
can
be
fading
/
temporary
• +
VE
Doppler
Shift:
If
the
distance
between

losses.
the
source
and
the
receiver
is
reducing,
the

received
frequency
appears
greater
than

that
transmitted.

DIFFRACTION
• Occurs
because
more
waves
are
detected


than
if
stationary.

• When
a
radio
wave
passes
a
solid
object,
• -­‐
VE
Doppler
Shift:
Distance
increasing
/

radio
energy
is
scattered.
frequency
appears
lower.

• Allows
radio
waves
to
be
received
behind
a
• Actual
wavelength
stays
the
same.

mountain.