Textron Cessna 172R, Pilot Operating Handbook

Page: 391 / 500

CESSNA
MODEL
172R
SECTION
9
-
SUPPLEMENTS
SUPPLEMENT
6
-
FAA APPROVED
ADF OPERATION NOTES:
r
ERRONEOUS ADF BEARING
DUE TO RADIO
FREQUENCY
PHENOMENA:
In the U.S., the FCC, which
assigns AM radio
frequencies,
occasionally will
assign the same
frequency
to
more than one
station in an area. Certain conditions, such
as
Night Effect, may
cause
signals
from such stations
to overlap. This should be
taken
into consideration when using AM broadcast station
for navigation.
Sunspots and atmospheric phenomena may occasionally distort
reception so that signals
from
two
stations on the same frequency
will overlap. For this
reason, it is always
wise to make positive
identification
of the station being
tuned, by switching the function
selector
to ANT and listening
for station
call letters.
ELECTRICAL STORMS:
In the vicinity
of
electrical
storms, an ADF indicator pointer tends
(
to swing from the station tuned toward the
center of the storm.
NIGHT EFFECT:
This is
a
disturbance particularly
strong
just
after sunset and just
after dawn. An ADF indicator pointer may swing erratically
at
these
times. If- possible,
tune to
the
most powerful station at
the lowest
frequency. If this is not possible, take the
average of pointer
oscillations
to
determine relative station bearing.
MOUNTAIN EFFECT:
Radio waves reflecting from the surface of mountains may cause
the pointer
to
fluctuate or show an erroneous bearing. This should
be taken into
account
when taking bearings
over
mountainous!
terrain.
f**
COASTAL REFRACTION:
Radio
waves may be
refracted when passing from land
to
sea or
when moving
parallel
to
the coastline.
This also
should
be taken
into
account.
Feb 28/00
S6-11
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