CESSNA
MODEL 172R
ADF OPERATION NOTES:
SECTION 9 - SUPPLEMENTS
SUPPLEMENT 6 - FAA APPROVED
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 ter
COAST AL 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.
Dec 2/96
S6-11
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