Yaesu FT-26 Technical Supplement page 15

for lowpass filtering, and then returned to varac­
tors D6001/D6002 (for the transmitter) and
D6003/D6004 (for the receiver) on the PLL Unit.
Changes in the level of the DC voltage applied
to the varactors affect the reactance in the tank
circuit of the VCO, changing the oscillating fre­
quency of the VCO according to the phase differ­
ence between the signals derived from the VCO
and the crystal reference oscillator. The VCO is
thus phase-locked to the crystal reference oscilla­
tor.
The output of receiver VCO Q6003, after buffer­
ing by Q6005, is delivered to the Main Unit for
amplification by Q1002 before application to the
1st mixer, as described previously.
Transmitter VCO Q6002
lates between 140 and 150 MHz according to the
) programmed transmit frequency. The remainder
of the PLL circuitry is shared with the receiver.
However, the dividing data from the microproces­
sor is such that the VCO frequency is at the actual
transmit frequency (rather than offset for IFs, as in
the receiving case). Also, the transmitter VCO is
modulated by the filtered speech audio applied to
the tank circuit at D6005, as described previously.
Transmit and receive 5-V buses select which VCO
)
is to be active by Q6004
ceiver) and Q6010
ter). FET Q6001 (28K880GR)
for application to the tracking bandpass filters in
the receiver front end on the Motherboard.
Transmit Inhibit
When the transmit PLL is unlocked pin 7 of PLL
chip Q6006 goes to a logic low, turning on Q6009
)
(2SA 1586Y) to raise the
is diode-ORed with the receive 5-V bus and ap­
plied to D4008 on the APC Unit to disable the
transmitter as described above under the APC de­
scription.
Miscellaneous Circuits
&
Battery Charger
DC
The EXT jack on the Motherboard applies
voltage to the B+ line through diode D1006 to
FT-26 Technical Supplement
(28C4226-R22)
for the re­
(DTC144EU,
(DTC144EU, for the transmit­
buffers the VCV line
UL
line. This unlock signal
Power Control
operate the transceiver, and through regulator
Q1005 (288799-ML)
the battery. The outer (negative) contact of the EXT
DC
jack disconnects the negative side of the bat­
tery from direct chassis ground connection, plac­
ing diode D1021 in line instead when a plug is
inserted in the jack. When the power is switched
on, the B+ line on the Motherboard feeds transmit­
ter RF power module Q1007 and the APC Unit
directly, and 5-V regulator Q1006. The B+ voltage
is also applied to Q2006
Unit for low battery indication, and to LED driver
Q2013 (2801366A)
LED indicator and display lamps.
Transmit/Receive Switching
oscil­
Closing the PTT switch on the Control Unit
pulls one side of the microphone low, which turns
on Q2008
(1 MZ1
essor Q2007 low. This causes pin 2 of Q2007 to go
low, and the resulting signal turns on Q1013
on the Motherboard to apply 5 volts to the
123YU)
TS line for the transmitter circuitry, and turns off
Q1012/Q1009
the receiver. Pin 18 of the microprocessor can also
be pulled low by amplified microphone audio
from Q2009 via VOX controller Q2010
when an external microphone is used and
124TU)
the VOX function is enabled by the microprocessor
via Q2012 pin 14.
When the Power Saver feature is activated by
the operator, the microprocessor periodically pulls
pin 79 low, which enables the 5-V buses for the
receiver via Q1010
mitting.
Beeper Q2005
pad beeps, passed via Q2011 to the Motherboard
for amplification along with receiver audio. The
other half of Q2005 is used to generate an 88.5-Hz
CTCSS tone in Japanese versions only, which is
filtered by Q2009-%. These stages are not used in
other versions.
Circuit Description
to the charging terminal of
(1 MZ1) on the Control
on the Control Unit for the
&
Power Saving
), pulling PTT pin 18 of microproc­
(DTC144EU/DTA143XU)to
CDT A 123YU) when not trans­
generates key­
(µPD4013BG-1;2)
(DTA-
disable
(DTC-