Yaesu FT-897 Technical Supplement page 8

Circuit Description
SSB/CW Demodulator Circuit
The 2nd IF SSB/CW signal passes through buffer am-
plifiers Q1088 and Q1081 (both BB305CEW) to the SSB
balanced demodulator Q1071 (SA602AD) which produc-
es audio by applying the carrier signal from the CAR-
DDS IC Q1062 (AD9835BRU). The demodulated audio
signal is stripped of high-frequency components by an
active low-pass filter, op-amp IC Q1120 (NJM2902V),
then is applied to the Audio Amplifier Circuit.
AM Demodulator Circuit
The 2nd IF AM signal passes through buffer amplifi-
ers Q1088 and Q1081 (both BB305CEW) to the AM de-
modulator D1055 (BAS316), yielding demodulated au-
dio signal which is applied to the Audio Amplifier Cir-
cuit.
Audio Amplifier Circuit
The demodulated audio signal is passed through AF
pre-amplifier Q1119 (NJM2902V) and electronic volume
control IC Q1087 (M62364EP) to the AF Amplifier IC
Q1105 (TDA2003H) which drives the internal or exter-
nal speaker to a maximum output of approximately 2.5
Watts.
Transmit Signal Circuitry
Microphone Amplifier Circuit
The audio signal from microphone jack on the MIC
Unit is amplified by audio amplifier Q1109 (2SC4154E)
on the MAIN Unit, and then is applied to electronic vol-
ume control IC Q1087 (M62364EP), the level of which
is set via the User Menu.
SSB Modulator Circuit
The output (audio signal) from the electronic volume
control IC is passed through audio amplifier Q1118
(NJM2902V) to the balanced modulator IC Q1071
(SA602AD) which produces a Double Sideband (DSB)
signal by applying the carrier signal from the CAR-DDS
IC Q1062 (AD9835BRU). The DSB modulated signal
(455 kHz) is fed to ceramic filter CF1004 (or the optional
mechanical filter) which strips residual carrier and the
undesired sideband, resulting in a Single Sideband (SSB)
signal.
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AM Modulator Circuit
As in the SSB modulator circuit, a carrier signal ap-
propriate to the transmitting mode (AM) from the CAR-
DDS Unit and an audio signal from the microphone are
applied to balanced modulator IC Q1071 (SA602AD).
The control signal from Mode Switch IC Q1003
(BU4094BCFV) causes a voltage ("AM 5V") to be sent
from transistor Q1058 (2SC4154E). This voltage is ap-
plied to IC Q1071 via D1059 (BAS316), causing the bal-
anced modulator to lose balance. The restored carrier sig-
nal and modulated signal are then fed to the TX mixer via
ceramic filter CF1004.
FM Modulator Circuit
The output (audio signal) from the electronic volume
control IC is passed through the pre-emphasis circuit which
consists capacitor C1492 and resistors R1493 and R1477,
a n d I n s t a n t a n e o u s D e v i a t i o n C o n t r o l Q 1 1 1 9
(NJM2902V), to the splatter filter which consists Q1119,
capacitor C1430, and resistors R1358 and R1384. The fil-
tered audio signal is applied to the FM modulator circuit,
which produces the FM signal. The FM modulator circuit
uses a voltage controlled crystal oscillator (VCXO) which
consists Q1055 (2SC4400), D1046 (1SV229), and
X1002 (22.7767 MHz).
1st IF Circuit/1st Mixer Circuit
The modulated SSB/AM signal is applied to the 2nd
Mixer Q1082 (SA602AD), which produces the 68.33
MHz 2nd IF signal utilizing the 2nd local signal (68.875
MHz). The 2nd IF signal is fed through the 2nd IF filter
XF1004 which strips away unwanted mixer products, then
passes through the 2nd IF amplifier Q1061 (BB304CDW)
to the double balanced mixer D1034 (HSB88WS) which
produces the transmit frequency by applying the local sig-
nal (68.430-538.330 MHz) from the PLL Unit. The trans-
mit signal is passed through a low-pass filter (1.8-29.7
MHz), a high-pass filter (50-54 MHz), a band-pass filter
(144-146 MHz), or a band-pass filter (430-450 MHz)
which consists of various inductors and capacitors. The
filtered transmit signal is amplified by Q1017 (2SC3357),
Q1011 (2SK2596), Q1006/Q1007 (2SK2973), and
Q1001/1002 (2SK2975), and is applied to the Power
Amplifier: Q3017/Q3018 (2SC5125: HF/50 MHz) or
Q3016 (2SC3102: 144/430 MHz).