Transmit Circuit; Drive Unit - Yaesu FT-901DM Instruction Manual

'TRANSMIT CIRCUIT
SsB
The output from the MIC jack Jy is fed throu!
the MIC GAIN control VRa {© pia 13 of the
CARRIER UNIT,
'CARRIER UNIT (PB-1706)
icrophone signal is amplified by mierophone
ter Qnys (TA-TO63PD and fed though relay
RLoo: (o the ring modulator, consisting of Dros
Drox (all 181007), where the signal modulates a
atrier signal delivered from Oyo (2SCI8ISY},
The double sideband signal is fed through Tyo,
to t h e FILTER UNIT.
FILTER UNIT (PB-1716)
The NOAT.S KIlz signal fed to pin 8 of the FILTER
UNIT is amplified by buffer amplifier Qyo4 (28K
TGR) and is passed through sideband filter XF yo
hy diode switches Dyoe (181588) and Dyo> = Dsos
{both 181007) where the DSB signal is converted
to am SSB signal by removing the unwanted side
NB UNIT (PB-1703)
'The SSI signal is fed through # buller amplifier
ine ESCIBISY) to the bases of Qzo2 2nd Qa0s
(bath 2SCISISY), When the RP processor switch
is "OFF." the SSB signal is amplified by Qzor
and fed 10 Qzoy (BSKS9GR), Wien the processor
'witch is "ON." the SSB signal is amplified by
soe QSCISISY) and is Farther amplified by
the Himiter Oso, €TA7O6OP). where the signals
hat exceed the preset clipping level ae sliced out.
Vikan is sed to equalize the level oF the clipped
and unclipped sisal
"This highly clipped SSB signal i paswed theough
a selective fter XFyo, to remove RF harmonies
that result from signal clipping, The filtered out
put signal is amplified by Qjo3 snd fed to the
RF UNIT. The PROC LEVEL control VR,>,
located on the front panel, varies the resistance
bbetwoen the collector and emitter of Qapy (28C
IBISY), thus changing the input signal level to
the filter.
"The CW, PSK, AM, and FM signals pass through
241 2SKIGR) and are fed 10,
The ALC (Automatic Level Control) voltage
detected at the grid citout of the PA tube Is fea
to the First gute of Qspy 10 reduce the gain of the
jinpliier, thus preventing overloading, and dis
tortion
RF UNIT (PB-1702)
The SSB signal from Jyoz of the printed board
js fed to the balanced mixer consisting of Qiee
and Quox_(hoth 3SK40M), where the SSH signal
is heterodyned to the desired RF frequency by
mixing with the local signal whieh is supplied
from the VCO UNIT. The mixer output is applied
throurh diode switeh (181555) to the
DRIVE UNIT,
Dros
DRIVE UNIT (PB-1714) PA UNIT (PB-1715),
{from the RE UNIT is fed to the eri
smitter driver Vigo (I2BY7A) where
it is amplified to a level sufficient to drive the
{inal amplifier tubes Vj 95. ad Vyy2 (6146B).
[A portion of the RF signal is coupled through
Cie to the cathode of the I2BY7A driver tube
s0 88 to improve the lineanty of the inal ampli
saze (RF negative feedback),
nation, The return of the gvid circuit is
wonnected to the REC A UNIT (PB1708) (0
produce ALC voltage to control the gain of the
TTX IF amplifier, t h u s preventing distortion caused
by oventive.