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 TM 55-1510-218-MTF
PROCEDURE
TROUBLESHOOTING
REFERENCE
AVIONICS FLIGHT CHECKS (CONT)
b. Mode selector (HF control
panel) - Set desired operating
mode.
c. Microphone switch - Press
momentarily and wait for an-
tenna coupler to tune. A 1000
Hz tone will be heard in the
headphones until tuning is
complete. Tuning time should
not exceed 30 seconds.
d. Establish
with a ground station at least
150 miles distant on at least
three frequencies (one each
from the lower, middle,, and
upper frequency ranges). Es-
tablish two-way communica-
tions on AM and, when possi-
ble, on USB AND LSB.
Obtain signal quality reports
from the other station and
note received signal quality.
NOTE
The intelligibility of SSB voice operations
becomes degraded when the receiver and
transmitter differ in frequency by a small
amount (approximately 50 Hz). The voice
pitch will sound either too high or too low.
The cause may be either the receiver or
e. Frequency accuracy - Check
as follows:
(1) Station WWV - Select the
frequency that provides
4-20
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