Yaesu FT-817 Technical Supplement page 11

AM Modulator Circuit
As in the SSB modulator circuit, a carrier signal from the
CAR-DDS Unit and an audio signal from the microphone
are applied to balanced modulator IC Q1087 (SN16913P)
on the MAIN Unit.
The control signal from MODE SW IC Q1021
(BU4094BCFV: Lot 1 - 76, CD4094BPWR: Lot 77 -) on
the MAIN Unit causes a voltage labeled "AM 5V" to be
sent from transistor Q1079 (2SC4154E). This voltage is
applied to IC Q1087 (SN16913P) via D1077 (BAS316),
causing the balanced modulator to lose balance. The re-
stored carrier signal and modulated signal are then fed to
the Tx mixer via ceramic filter CF1004 (CFJ455K14) on
the MAIN Unit.
Frequency Modulation Circuit
The FM circuit uses a voltage controlled crystal oscillator
(VCXO) which consists mainly of Q1033 (2SC4400),
X1001 on the MAIN-Unit, varactor diode D1056 (1SV229),
and T1018. The VCXO has a center frequency of
22.7785MHz.
The FM signal is produced by applying a signal from the
FM microphone amplifier circuit to varactor diode D1056
and varying the crystal oscillator load capacity in propor-
tion to the signal voltage.
CW (A1) Signal Generator Circuit
When the transmitting mode is CW (A1), the control sig-
nal from D-A converter IC Q1077 (M62353GP) on the
MAIN Unit creates a "CW 5V" voltage. The voltage is ap-
plied to balanced modulator IC Q1087 (SN16913P) via
D1071, providing a carrier from the balanced modulator
for the input to the transmit signal circuit of the MAIN Unit.
1st IF Circuit/1st Mixer Circuit
The 455 kHz 1st IF signal from the modulator circuit is
band-limited by the MAIN Unit's ceramic (CF1004) or
optional mechanical filter U1003 (XF5201 or XF5301) ac-
cording to the selected mode (CW, SSB, or AM). It is then
buffer-amplified by FET Q1040 (BB301CAW) and fed to
1st mixer IC Q1038 (SN16913P).
The IF Unit's double balanced mixer IC Q1038
(SN16913P) is used as the 1st mixer. A local signal
(67.875MHz) is produced by tripling the Reference fre-
quency at Q1047 (2SC4400), and this local signal is fed
to the "local" port of the doubly-balanced mixer IC, where
it is mixed with the 455 kHz 1st IF signal to produce a
68.33MHz 2nd IF signal.
Circuit Description
2nd IF Circuit/2nd Mixer Circuit
The 2nd IF signal passes through crystal filter XF1001 and
then is fed to the 2nd mixer circuit.
The 2nd mixer consists of the MAIN Unit's D1049
(HSB88WS). The 2nd local signal (68.430-538.330MHz)
from the PLL Unit is applied to the gates of each FET in
the 2nd mixer.
High-Frequency Transmit Preamplifier Circuit
The transmit 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 (430-440
MHz) and then is amplified by Q1001 (UPC2710), and
passed onward to the PA Unit via J1002.
Power Amplifier Circuit
The transmit signal from the MAIN Unit arrives at con-
nector J3001 on the PA Unit.
The transmit signal (1.8 MHz to 430 MHz) delivered to
the PA Unit is amplified by pre-driver Q3001 (2SC3357),
driver Q3002 (2SK2596) and final amplifiers Q5401/
Q5402 (2SK2975: Lot 1 - 74, RD07MVS1: Lot 75 -).
Low-Pass Filter (LPF) Circuit
The transmission signal from the power amplifier circuit
is passed through a low-pass filter which consist mainly
of RL3001-RL3015, RL3017, and corresponding inductor
and capacitor networks. The LPF is a 5th or 7th-order
Chebyschev type filter, utilizing nine different sections
for the various amateur bands at 1.8 ~ 430 MHz.
The low-pass filtered transmission signal is fed to the
FRONT ANT connector (J0001) or REAR ANT connector
(J0002) through the triplexer and directional coupler.
The directional coupler samples a part of the transmis-
sion power to detect forward power and reflected power.
A DC voltage corresponding to the relative forward/re-
flected power is produced by D3032/D3033 (both MA716,
1.8 to 54 MHz), D3009/D3017 (both MA716, 144 to 148
MHz), or D3007/D3008 (both MA716, 430 to 450 MHz) ,
and is used for automatic level control (ALC).
ALC Circuit
The output from the directional coupler is routed from
connector J3004 and applied to the ALC circuit via con-
nector J1003 on the MAIN Unit.
The ALC circuit consists of an op-amplifier circuit for
amplifying the forward and reflected voltage, a time-con-
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