Piper ARCHER III Pilot Operating Handbook page 291

PA-28-181, ARCHER Ill
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SECTION 4 - NORMAL PROCEDURES (continued)
ADF Operation NOTES:
Erroneous ADF Bearing D11e
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 condi­
tions, 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.
Eleclrical S1orms:
ln the vicinity of electrical storms, an ADF indicator pointer Lends to swing rrom
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the station tuned toward the center of the storm.
Night Effec1:
This is a disturbance particularly strong just after sunset and just arter 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 rellecting from the surface of mountains may cause the pointer to
lluctuate or show an erroneous bearing. This should be taken into account when
taking bearings over mountainous terrain.
Coastal Re. f raction:
Radio waves may be rerracted when passing from land to sea or when moving
parallel the coastline. This also should be taken into account.
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ISSUED: December 22, 2017
REVISED: May 7, 2018
Radio Frequenc,· Phenomena:
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SECTION 9
SUPPLEMENT 2
REPORT: VB-2749
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