Yaesu FT-901DM Maintenance Service Manual page 21

GENERAL
OPERATION
The tuning procedure for this transceiver is not
complicated. However, care should be exercised
when tuning so that peak performance of the
equipment is secured. The following paragraphs
describe the procedure for receiver and transmitter
operation.
INITIAL CHECK
Before connecting the transceiver to a power
source, carefully examine the unit for any visible
damage. Check that all modules are firmly in
place and that the controls and switches are op-
erating normally. Make sure that the voltage spe-
cification marked on the rear panel matches your
supply voltage, and that the line fuse on the rear
panel matches the supply voltage; for 117 VAC,
use a 5 amp fuse, and for 220 VAC use a 3 amp
fuse. For DC operation a fuse holder is installed
in the DC cable, and a 20 amp fuse should be
installed here.
FREQUENCY SELECTION
Frequency readout for the FT-901DM _ includes
both analog and digital readout. The analog read-
out dial shows calibrations at the 100 kHz and
10 kHz points, and is marked, as well, in 1 kHz
increments for fine tuning. The digital readout
displays all digits of the operating frequency, with
resolution down to 100 Hz accuracy.
RECEIVE OPERATION
(1) Preset the controls and switches as indicated:
POWER..... . OFF
HEATER.... : OFF
VERO ise win one xs Switch depressed
VOX GAIN. . .PTT position
RF GAIN ... .Fully clockwise
AFGAIN ....Adjust subsequently for com-
fortable level
Desired band
-Desired mode
PRESELECT. .Desired band segment
(2) Turn the POWER switch to ON. The meter
will light up and the operating frequency
will be displayed on the dial window. Adjust
the AF GAIN control for a comfortable
listening level, and adjust the PRESELECT
control for maximum receiver noise or signal
level. The PRESELECT control may require
repeaking as the main tuning dial is tuned
across the band.
(3) The RX CLARIFIER may be utilized if the
received signal is drifting. Pushing the RX
button and rotating the CLARIFIER control
will provide a means of offsetting the receiver
frequency +2.5 kHz without changing the
transmitting frequency. A red LED indicator
will light up when the CLARIFIER is in use.
(4) When pulse-type noise is encountered, the
NB (Noise Blanker) switch should be acti-
vated, providing effective suppression of
this type of noise.
(5) Rejection of adjacent-channel interference
may be accomplished by several means. The
REJECT control may be utilized to place a
steep-skirt 30 dB notch attenuation on any
interfering signal within the IF passband.
The WIDTH control varies the passband of
one of two IF filters (the other is fixed and
presents a boundary for narrowing the pass-
band). Varying the WIDTH control varies the
IF selectivity from approximately 300 Hz to
2.4 kHz (at 2.4 kHz the WIDTH control is at
"0" and the two filters have the same pass-
band). Clockwise rotation from the center
("0") position makes the passband narrow
toward the high frequency side, while
counter-clockwise rotation narrows the pass-
band on the low-frequency side.
(6) For CW reception, the APF (Audio Peak
Filter) may be activated. This filter has a
100 Hz peak bandwidth with very steep
skirts so as to provide single-signal reception
for CW, with insertion loss of less than 1 dB
when the APF control is tuned exactly to
the signal frequency. The APF FREQ control
varies the peak frequency from approximately
400 Hz to 900 Hz. The operator will observe
that the APF system provides a significant