Yaesu FT-2500M Technical Supplement page 11

t
Description
phase detector section of
Q1.024,
which produces
a dual 5-V pulsed output with
pulse duration
depending on the phase difference between the
input
signals. This pulse train
is converted to
DC
by
charge
pump
Q1026/QI027
(lMXs
/lMZ2),
lowpass
filtered, and then fed
back to varactors
D301 and D302 (1T363 x 2) on the VCO Unit.
Changes
in the level of the DC voltage applied
to
D30L/D302 affect the
reactance
in
the
tank
circuit of VCO
Q301,
changing the oscillating fre-
quency according
to
the
phase difference be-
tween the signals derived from the VCO and the
crystal reference oscillator.
The VCO
is
thus
phase-locked to the crystal reference oscillator.
The
output
of receiver VCO Q301, after
buffer-
irg
by
Q305,
is
delivered
to the Main Unit for
amplification by
Q1005
before application to the
1st
mixer,
as
described previously.
Transmitter VCO Q303 (2SC3356)
oscillates
between
140
and 174MHz according to the pro-
grammed transmit frequency. The remainder of
the PLL circuitry
is
shared
with
the
receiver.
However, the dividing data from the micro-
processor 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
modulating varactor D305, as de-
scribed previously.
Transmit
Inhibit
When the transmit PLL is unlocked
pin
7
of
PLL
chip
Q1024 goes
to
a
logic low, tuming
on
Q1020
(DTA143EK) and tuming
off half of Q1018.
This unlock signal produces
a
low
impedance at
the
base
of
the other
half of
Q1018,
which
then
turns off Automatic Power Controller
Q1019 to
disable the
supply voltage to transmitter
RF
am-
plifiers
Q1009 and Q1010,
disabling
the
transmit-
ter.
Mis
cell
ane
ous Cir
cuits
Power-On
Sequencing
I
Panel Lamps
Pressing the
POWER
switch on the
DISP
Unit
turns
onQ2017 (DTC114EK) on the CNTL Unit,
applying 5 volts from regulator
Q2012 (L7805)
via 9-volt regulator Q1013 (AN6541
)
and the 13.8-
V supply line to
the base of Q2016 (2581140S).
This
pulls
RESET
pn75
of microprocessor Q2006
low, causing PO
pin
66
to
go
high. The
PO line
then
pulls
the base
of
Q2017 (DTC114EK) low,
lighting
the
pilot
lamps via Q2005 (25C2712GR)
and Q2004 (2SB1143S). Lamp brightness is con-
trolled by
CdS photosensor
CS3001,
which pro-
vides an
input
to microprocessor
Q2006,
pn
49.
An pulsed DC ouput
is then applied to the inte-
grator circuit
formedby
C2015
and M021, which
produces
a DC bias proportional to
the
pulse
train input, which is then applied to
the base
of
Q200s (2S,C2712GR),
and
Q2004
(2SB1143S),
controlling voltage
to
the panel and display
lamps.
P
u
sh-Tb
-Talk
Tr
an
s
mit
Ac
t
ia
at
i
o
n
The PTT switch on the microphone is connec-
ted to
pn
44
of
microprocessor
Q2006,
so that
when the switch
is closed
pn69 (tx/rx)
goes
low.
This signal is delivered to power bus controller
Q1021
(lMHs) on the
MAIN Unit,
which
then
disables the receiver by disabling the 9-V supply
bus at QI022
(DTA143EK)
to the front
end,
IF,
discriminator and receiver VCO circuitry.
At
the
same
time,
Q1015 (2581143S) activates the
transmit 9-V supply line to enable the transmit-
ter.
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FT-2500M Technical Supplement