Yaesu FT-901DM Maintenance Service Manual page 22

improvement in signal-to-noise ratio. The
selectivity of the APF circuit may be varied
by adjusting VReo, under the top cover.
(7) For extremely strong signals, the ATT (RF
attenuator) switch may be pressed to activate
a 20 dB attenuation of the incoming signal.
This should prevent any chance of overload
of the receiver front end.
TRANSMITTER TUNE-UP
The following tune-up procedure must be per-
formed prior to commencing operation on the
desired mode: LSB, USB, CW. FSK. AM. or FM.
See the. paragraphs relating to the specific mode
after basic transmitter tune-up is described.
Connect a dummy load or matched antenna to
the coaxial fitting on the rear apron. Preset the
controls as follows:
POWER. 2s OFF
HEATER. ......OFF
CARR.........Fully counter-clockwise position
MIC GAIN. .. . . .Fully counter-clockwise position
WMG v6 oi0.2¢ a e OPF
METER switch . IC
SPEEET o3 sev swe VFO (Depressed)
BAND... . Desired band segment
MORE... 6. SB or LSB
PLATE . Desired band segment
PRESELECT. . . .Desired band segment
LOADING. ..... To position shown in table
PROC .. . OFF (Not depressed)
TUNE. 226.04 OFF (Not depressed)
CLAR TX. . OFF (Not depressed)
VOX GAIN... . PTT position
Turn the POWER and HEATER switches to ON.
From a cold start, allow 60 seconds after the
HEATER switch is turned on for warm-up of the
transmitter tubes. Be certain that the accessory
plug is inserted in the accessory plug is inserted
in the accessory socket: without this plug being
so connected, there will be no power applied to
the tube heaters. Heater voltage is supplied through
pins | and 2 of the accessory socket.
GENERAI
LOADING POSITIONS
BAND POSITION
160 5
[80 4
| 40 3.5
L230. 3 |
1s 2.5 |
110A 3
| 10B 3
[_10¢ 3
10D 3
Note LOADING positions are nominal. Minor
variations from positions shown are to
be expected.
Set the VOX GAIN control to MOX. The meter
will now read final amplifier resting cathode
current. This should read .05 (50 mA).* If it is
not, adjust the bias control located under the top
cover near the rear of the set. Set the METER
switch to ALC and adjust the ALC control under
the top cover for full scale deflection of the meter.
Returm the meter switch to IC and the VOX GAIN
control to PTT.
*Note: On the FT-901SD, resting cathode
current should be .025 (25 mA).
PRE-TUNING
(IMPORTANT NOTE: Subsequent transmitter
tuning utilizes the TUNE button instead of MOX
for actuating the transmitter. When pressed, the
TUNE button causes the transmitter to be acti-
vated for ten seconds, after which time the FT-
901DM returns to the receive condition. This is
a protective feature that should not be nullified
by use of the MOX control.)
(1) Adjust the PRESELECT control for maxi-
mum receiver noise level.
(2) Depress the TUNE button. Rotate the CARR
control until the meter reading rises just
above the normal idling current of .0S (50
mA).
(3) Adjust the PRESELECT control for a maxi-
mum meter indication.
Caution: if the meter reading exceeds .1 (100
mA) reduce the setting of the CARR control.