Yaesu FT-901DM Maintenance Service Manual page 13

GENERAL
(8) PRESELECT
This control pretunes the signal circuits for both
transmit and receive. The PRESELECT circuit
provides continuous permeability tuning through-
out the frequency range of the transceiver.
(9) BAND
The BAND switch provides selection of the band
desired, 160 through 10 meters plus WWV/JJY
(receive only).
(10) RF GAIN/CLARIFIER
The RF GAIN and CLARIFIER controls are
mounted on concentric shafts. The RF GAIN
control provides manual control of the gain levels
of the RF and IF amplifiers on receive.
The CLARIFIER control allows manual offset of
+2.5 kHz of either the transmit or receive fre-
quency. Selection of transmit or receive clarifier
is made hy the two silver pushbuttons to the
left of the CLARIFIER control.
(11) ATT
The ATT (RF attenuator) button provides inser-
tion of a 20 dB attenuator in the incoming signal
path to minimize receiver cross modulation caused
by extremely strong local signals.
(12) PROC LEVEL/AF GAIN
The PROC LEVEL and AF GAIN controls are
mounted on concentric shafts. The PROC LEVEL
control allows manual control of the output level
of the RF speech processor. The processor is
actuated by pressing the silver pushbutton to the
left of the PROC LEVEL control.
The AF GAIN control adjusts the audio output
level at the speaker and phone jack. Clockwise
rotation increases the audio output.
(13) TUNE
This pushbutton, when depressed, places the trans-
mitter in the "tune" condition for ten seconds
for tuning purposes. After ten seconds, the trans-
ceiver is returned to the receive mode so as to
prevent damage to the final amplifier tubes caused
by excessive "key down" time during tune-up.
(14) LOADING.
This control tunes the output circuit of the pi net-
work to match the antenna/feedline impedance.
(15) PLATE
This control tunes the plate circuit of the final
amplifier.
(16) CALIB
When the MARK switch is activated, the CALIB
knob provides manual control for zeroing the
calibration of the digital display with the cali-
brator signal.
(17) CARR/KEYER
The CARR and KEYER controls are mounted
on concentric shafts. The CARR control varies
the amount of carrier in the CW, AM, FSK, and
FM models of operation.
The KEYER control varies the speed of the
built-in Curtis 8043 IC electronic keyer.
(18) VOX GAIN
This control selects MOX/PTT/VOX transmitter
relay control as well as adjusting the sensitivity of
the VOX circuitry. The PTT position provides
push-to-talk operation from a microphone PTT
switch or a footswitch. The MOX position provides
manual transmit. It must be returned to the PTT
position for receiver recovery.
(19) APF FREQ
This knob, when actuated by turning on the APF
switch, provides manual control for peaking the
audio peak frequency (APF) circuit on the desired
signal. This control will find its chief usefulness
on CW, because its bandwidth is much too narrow
for normal SSB reception.
(20) SQL/MIC GAIN
The SQL and MIC GAIN controls are mounted on
concentric shafts. The SQL control sets the squelch
threshold level for FM reception.
The MIC GAIN control varies the audio level from
the microphone amplifier stage. The control has
sufficient range to permit the use of any low im-
pedance (500 - 600 Ohm) crystal or dynamic
microphone. Clockwise rotation increases the level
of output from the microphone amplifier stage.
(21) FUNCTION SWITCHES: AMGC, APF/MONI,
AGC, PO/IC/ALC, and NB/MARK
The AMGC switch activates a microphone gain
threshold circuit which requires a_ particular