Yaesu FT-901DM Maintenance Service Manual page 23

GENERAL
(4) Rotate the PLATE control for a minimum
meter reading ("dip" in final amplifier
cathode current).
(5) Push the TUNE button again to return the
transceiver to the receive condition.
FINAL TUNING
Final peak tuning utilizes the relative power out-
put position of the METER switch. At full rated
power into a 50 Ohm load, the meter will read
approximately 1/2 to 2/3 full scale. If the PO
reading is too high (off scale) or too low (1/4 scale
or less) and the load impedance is very close to
S50 Ohms, the PO ADJ control on the rear apron
may be adjusted so as to provide 1/2 to 2/3 scale
deflection at full power. Once the PO meter is
calibrated, off-scale meter deflections are the
result of reflected power due to high SWR, and
corrective action may be required in the antenna
system.
Final transmitter peaking is described below:
(1) Set the METER switch to the PO position
and rotate the CARR control to the II
o'clock position.
(2) Press the TUNE button and rotate the PRE-
SELECT control for a maximum meter read-
ing. Press the TUNE button again to return
to the receive condition.
(3) Press the TUNE button and rotate the LOAD-
ING control for a maximum meter reading.
Press the TUNE button again to return to
the receive condition.
(4) Press the TUNE button and rotate the PLATE
control for a maximum meter reading. Press
the TUNE button again to return to the re-
ceive condition.
(5) Repeat steps 2 through 4, advancing the
CARR control approximately 2 units for
each set of adjustments until the CARR con-
trol is fully clockwise. The transmitter is now
tuned for maximum power output.
(6) Return the CARR control to the fully coun-
ter-clockwise position. Return the METER
switch to IC.
With familiarity, some of steps 2 - 4 may be per-
formed within one press of the TUNE button,
taking advantage of the 10-second timer. The
operator is discouraged, through, from exceeding
the 10-second limitation imposed by the timer
through use of the MOX position or the micro-
phone PTT switch.
SSB OPERATION
After completion of the above tuning procedure.
set the MODE switch to USB or PSB as desired.
Set the VOX GAIN control to PTT aid activate
the transmitter by pushing the nucrophone PTT
switch or the footswitch, if used. While speaking
in a normal voice into the niicrophone, advance
the MIC GAIN control until the meter Mieks down
to the midscale of the green-colored portion of
the meter scale
Note: When the METER switch is set to IC,
voice modulation peaks will indicate 150 -
200 mA, Actual peak cuureat: however, is
approximately 2 times the indicated value
To set the sensitivity of the VOX system, begin
with the VOX GAIN control in the PEP position
Advance the VOX GAIN and speak in a normal
voice. The VOX GAIN control should be advanced
until the voice actuates the transmitter (do not
press the microphone PTT switch or tootswitch, if
used, during this adjustment).
Set the antitrip potentiometer under the top
cover to the minimum point which preveuts the
speaker output from tripping the VOX, Do not
use more VOX GAIN nor antitrip than necessary
Adjust the delay potentiometer under the top
cover for the desired release time.
If desired, the AMGC circuit may be activated.
This circuit acts as a "microphone squeleh;" that
is. it initiates a threshold for microphone input
which must be exceeded before output from the
microphone amplifier will occur. This feature
permits minor noises such as a VV tu the operating
room to be present without gomg out over the
air. Adjustment of the AMGC delay time is made
by a control under the top cover
RF SPEECH PROCESSOR ADJUSTMENT
(All models)
The FT-901DM speech processor, when properly
adjusted, is designed to improve the intelligibility
threshold at the receiving end by increasing the
average SSB power output. RF clipping is applied
to the IF signal, which is then filtered to remove
harmonics and out of band intermodulation
products.