Yaesu FT-901DM Maintenance Service Manual page 14

minimum input level from the microphone to
trigger the microphone amplifier. Low-level back-
ground noise will not activate the transmitter
with the AMGC in operation. This circuit may be
considered a "microphone squelch" system. The
M GAIN control functions normally with the
AMGC system in operation.
When the APF/MONI switch is in the APF posi-
tion, the audio peak filter (APF) circuitry
is activated. The exact frequency of the audio
peak is set by the APF FREQ knob. When this
switch is placed in the MONI position, monitor-
ing of the microphone level may be accomplished
for operator convenience or tape recording both
sides of a QSO. In the CW mode, CW sidetone
will be heard regardless of the position of the
APF/MONI switch.
The AGC switch controls the length of the re-
covery time for the receiver AGC circuitry. This
switch provides slow or fast recovery, and will
also turn off the AGC if desired.
The NB/MARK switch provides for actuation of
either the Noise Blanker (NB) or crystal calibrator
(MARK). The marker oscillator can produce cali-
bration signals at intervals of either 25 kHz or
100 kHz by proper positioning of a switch inside
the cabinet.
(22) POWER
This is the main on/off switch for the transceiver.
In the OFF position, the memory circuits are
disabled, so that when the transceiver is turned to
ON again, the memory circuits will have to be
reset.
(23) HEATER
GENERAL
ready for operation. This switch operates in both
the AC and DC modes.
(24) PHONES
This is a standard 1/4" phone jack for accom-
modation of headphones. The internal speaker is
disabled when headphones are plugged into this
jack.
(25) MIC
This four-conductor jack accommodates the
microphone plug for microphone input as well as
for PTT actuation.
Headphone plug