Circuit Descrip Ti O N - Yaesu FT-2400H Technical Supplement

Receive Signal Path
Incoming RF from the antenna jack is delivered
to the Main Unit and passed through a lowpass
filter and a 14 -wave antenna switching network
consisting of coils 11003
&
C1004, and diodes D1001
within the frequency range of the transceiver are
then passed through a varactor-tuned bandpass
filter consisting of T1001/T1002 before
cation by Q1001 (3SK131
then bandpass filtered again by varactor-tuned
resonators T1003/T1004, to ensure pure in-band
input to 1st mixer Q1002/Q1003
Buffered output from the VCO Unit is amplified
)
by Q1005
(2SC2759)
and C1042/C1043, to provide a pure 1st local sig­
nal between 118.6 and 152.6 MHz to the 1st mixer.
The 21.4-MHz 1st mixer product is passed through
dual monolithic crystal filter XF1001 (± 7.5 kHz
BW) to strip away all but the desired signal, which
is then amplified by Q1004
The amplified 1st
subsystem IC Q1008
the 2nd mixer, 2nd local oscillator, limiter amplifier,
noise amplifier, S-meter amplifier and squelch
gates. A 2nd local signal is generated from 21.855
MHz crystal X1001, which produces the 455 kHz
IF
2nd when mixed with the 1st
IF
Q1008. The 2nd is passed through ceramic filter
CF1001 to strip away unwanted mixer products,
and then applied to the limiter amp in Q1008,
which removes amplitude variations in the 455
kHz IF b e fore detection of the speech by ceramic
discriminator CD1001.
Detected audio is delivered from Q1008 to the
Interface Unit, where it passes through audio mut­
ing analog switch Q3005
phasis, high-pass and low-pass filtering by Q3006
-2/4
(NJM2902M-%,
gate, Q3012 (DTC114TK),
is then combined with beeper audio originating
from the microprocessor through Beeper volume
trimmer VR3002 and lowpass filter Q3006
2902M-%). The level of the combined receiver and
beeper audio on the Interface Unit
potentiometer VR2002 on the Control Unit (via
J3003 pin 3) and is then returned the Main Unit for
amplification by Q1023
for the optional headphone jack or 8-ohm loud­
speaker.
CIRCUIT " D ESCRIPTION
&
11004, capacitors C1003
&
D1002. Signals
RF
amplifi­
). The amplified RF is
x
(2SK302
and lowpass filtered by 11009
(2SC2714).
IF
signal is applied to FM IF
(MC3372M), which contains
IF
signal within
before de-em­
(TC4S66F)
&
-1/4). Another audio muting
passes the signal, which
is
set by
(TDA2003) up to 2 watts
Squelch Control
The squelch circuit consists of noise amplifier
Q1007 (2SC2712GR)
squelch trigger within Q1008 on the Main Unit, and
control circuitry within microprocessor Q2001
(HD404719-A11 H)
When no carrier is received, noise at the output
of the detector stage in Q1008 is amplified by
Q1007 and highpass filtered by the noise amp sec­
tion of Q1008, and then rectified by D1012 to pro­
vide a DC control voltage for the squelch switching
section within Q1008. With no carrier, pin 14 of
2).
Q1008 is high. This signal is inverted by Q1006
(IMH5) and delivered to BUSY pin 16 of main mi­
croprocessor Q2001 on the Control Unit as the Scan
Stop signal, which causes the
the display when the squelch is open. This signal
also causes the microprocessor to cut receiver
audio in two places on the Interface Unit men­
tioned already: opening audio mute gate Q3005
(via switch Q3004,
audio line to ground just before the audio amplifier
at Q3012, thus silencing the receiver while no sig­
nal is being received, and during transmission.
When a carrier appears at the discriminator,
noise is removed from the output, causing pin 14 of
Q1008 to go low. This signals the microprocessor to
activate the
Q2002
(LC7582).
for CTCSS tone detection from the FTS-17 A Tone
Squelch Unit (if installed), and for Digital Code
Squelch information (if the FRC-6 DCS Unit is in­
stalled). If not transmitting and tone squelch is not
activated, or if the received tone matches that pro­
grammed, the microprocessor switches Q3004/ -
Q3005 and Q3012 to allow audio to pass to the
amplifier and loudspeaker.
Center-Stop Scanning
To ensure that scanning stops at the center of a
detected signal, discriminator output from pin 9 of
Q1008 is also delivered to comparator circuit
(NJM-
Q3008 {LA6324M-2/4
VOL
which compares the discriminator output to a pre­
set DC level. The output of the comparator con­
nects to the Scan Stop line, preventing the received
signal from signalling the microprocessor to stop
scanning until the signal has been tuned to its peak
level, preset by Center-Stop trimmer VR3004.
and a highpass filter and
on the Control Unit.
BUSY
DTC114EK), and pulling the
BUSY
indicator through LCD driver
The microprocessor then checks
&
- % ) on the Intefac e Unit,
indication on