Yaesu FT-902DM, Instruction Manual

Page: 47 / 55

2.
VOX ADJUSTMENT
Tune in a signal and adjust the AF GAIN con trol
for a n ormal listening level. With the microphone
positioned near the speaker, increase the VOX
GAIN control on the front p anel until the speaker
output causes the VOX relay to switch t o the
transmit mode. Set the ANTITRIP con trol V R 6 0 1
. on P B- 1 846 to the point that will just prevent the
speaker output from tripping the VOX relay .
Speak into the microph one in a normal voice to
see i f one's voice will activat.e the VOX relay . If
not, VR6 0 1 may be advanced too far.
Adjust the DELA Y con trol V R 6 0 2 for the desired
release d elay. Cl ockwise rotation of V R 6 0 2 will
increase the delay tim e . For CW semi-break-in
operation , V R 6 0 2 should likewise be adjusted to
·
suit the operator's preferences. For CW operation
with a footswitch for relay actuation , the VOX
GAIN control may b e rotated fully coun ter­
clockwise (but n o t to the click-stop . which is the
MOX p osition ) to disable the VOX system.
3 . CW SIDETONE LEVEL
Adjustment of the CW sidetone level may be
made by adjustment of p otentiome ter V R 6 0 3 ,
located on PB- 1 84 6 , while the transceiver is being
keyed.
Q515
Q513
Q512
Q514
Q5oa
VOX/M a r ker
unit
PB- 1846
4 . CARRIER BALANCE
The transceiver should be allowed to reach n ormal
operating temperature b e fore making carrier
balance adj ustmen ts.
Tune u p the transceiver for SSB operation u sing a
matched an tenna or dummy load . Turn the MIC
GAIN control fully counterclockwise to rem ove
all audi o input from the modulator stage .
With the MODE switch set to either LSB or USB ,
turn the VOX GAIN control to MOX an d adjust
the carrier balance controls VR7 0 1 and TC 7 0 5
on P B- 1 7 06A for
a
minimum me ter reading with
th e METER switch in the PO position .
A more p recise b alance may b e ob tained b y tuning
a receiver which has an S meter to the transmitted
frequency . Adjust VR 7 0 1 and TC 7 0 5 for a mini­
mum S me ter reading on the remote receiver
while switching the MODE switch back an d forth
between the two SSB p ositions ; this will help
ensure good carrier suppression on both LSB and
U S B .
5 . AMGC ( Automatic Mic Gain Control )
The hold time of the AMGC system is adjusted
by VR7 0 2 on PB- l 7 06 A ; clockwise rotation of
\LR7 0 2 will provide a longer h old tim e .
6 . CARRIER F REQUENCY ADJU STMENT
Tun e up the transmitter on 20 me ters in the USB
m od e , using
a
dummy load. Apply a 1 kHz audio
signal to the mi crophone input and adjust the
audio generator output for 30 watts output from
the transmi tter as me asured by the dummy load
wattme ter. Shift the audio generator outpu t
frequency to 3 00 Hz without changing its output
level. Adjust TC 7 0 1 un til the power outpu t be­
comes 8 watts. Repeat this procedure for the
LSB mode .
NOTE : Recheck the carrier balance a fter ad­
justing the carrier frequency.
Connect a frequency c ounter to pin 1 7 o f the
N B UNIT PB- 1 9 9 4. Transmi t in the AM mod e .
S e t TC 7 0 3 for a reading o f 8 9 8 8 . 2 9 5 k Hz on the
fre quency counter.
Transmit on the FSK mode. Set TC 7 0 4 a re ading
of 8 9 8 8 . 1 2 5 kHz on the frequency coun ter. Re­
peat this procedure for AM and then FSK until
both frequencies are . indicated correctly on the
coun ter. Ground the inner conductor of the FSK
j ack on the rear p anel and confirm that the fre­
quency shifts to 8 9 8 8 . 29 5 kHz.
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