Icom IC-E90 Service Manual page 10

(3) 76.0 MHz–229.995 MHz RF CIRCUIT
The signals from the antenna switching circuit pass through
the attenuator (D351), and then applied to the bandpass fil-
ter (D352, D353, L351, L352) to suppress unwanted signals.
The signals pass through the bandpass filter (D354–D356,
D359, L354, L355, L357, L358, C357–C364) after being
amplified at the RF amplifier (Q351).
(4) 230.0 MHz–629.995 MHz RF CIRCUIT
The signals from the antenna switching circuit are applied to
the band switch (D457), and then pass through the attenua-
tor (D401). The signals pass through the bandpass filter
(D402, D403, L401, L402, C402, C404–C406) to suppress
unwanted signals, then applied to the RF amplifier (Q401).
The amplified signals pass through the bandpass filter
(D405, D407, L409, C414, C415), and are then amplified at
the RF amplifier (Q402).
(5) 630.0 MHz–999.990 MHz RF CIRCUIT
The signals from the antenna pass through the high-pass fil-
ter (L3, L4, C6–C8), and then applied to the attenuator
(D451) after being passed through the band switch (D10).
The signals pass through the bandpass filter (D452, L451,
C451–C454), then applied to the RF amplifier (Q451). The
amplified signals pass through the bandpass filter (D453,
D454, L452, L453, C456, C460, C462–C464) and RF ampli-
fier (Q452).
The amplified or filtered signals pass through one of the band
switch (D303, D313, D358, D408, D455), and then applied to
the 1st mixer circuit (IC351, pin 1).
4-1-4 1ST MIXER AND 1ST IF CIRCUITS (RF, AF
AND VCO UNITS)
The 1st mixer circuit converts the received RF signals to a
fixed frequency of the 1st IF signal with a PLL output fre-
quency. By changing the PLL frequency, only the desired fre-
quency will pass through the bandpass filter at the next stage
of the 1st mixer.
• RF CIRCUIT
1st LO signal
from the VCO circuit
1st IF signal to the AF unit
(AM, FM: 69.45 MHz,
WFM: 13.35 MHz)
SW
1st mixer
D303
(IC351)
SW BPF
D313
SW
D358
Q402
RF
SW
D408
Q452
RF
SW
D455
The amplified or filtered RF signals are mixed with 1st LO
signals at the 1st mixer (IC351) to produce a 69.45 MHz 1st
IF signal. The 1st IF signal is output from pin 6, and passed
through the bandpass filter (Narrow: AF unit; FI101, Wide: AF
unit; FI102) to suppress unwanted harmonic components via
the mode switch (AF unit; D101, D102). The filtered 1st IF
signal is applied to the IF amplifier (AF unit; Q102). The
amplified signal is applied to the 2nd mixer circuit.
The 1st LO signals (53.350 MHz–99.345 MHz, 99.350
MHz–560.545 MHz or 281.675 MHz–534.720 MHz) are gen-
erated at the 144 MHz VCO (VCO unit; Q3–Q5, D3, D4) or
430 MHz VCO (VCO unit; Q1, Q2, D1) circuits. The oscillat-
ed signal is applied to the 1st mixer via the doubler circuit
(Q354, D357) or directly.
4-1-5 2ND IF AND DEMODULATOR CIRCUITS
(AF UNIT)
The 2nd mixer circuit converts the 1st IF signal to a 2nd IF
signal. A double conversion superheterodyne system (which
converts receive signals twice) improves the image rejection
ratio and obtain stable receiver gain.
The FM IF IC (IC151) contains 2nd local oscillator, 2nd mixer,
limiter amplifier, quadrature detector and S-meter detector
circuits.
The amplified 69.45 MHz 1st IF signal from the IF amplifier
(Q102) is mixed with the 2nd LO signal at the 2nd mixer
(IC151) to produce a 455 kHz 2nd IF signal. The 2nd IF sig-
nal from the IC151, pin 3 passes through (AM and FM mode)
or bypasses (WFM mode) the 2nd IF filter (FI151) where
unwanted heterodyne signals are suppressed via the mode
switch (D151, D152). The filtered signals are applied to the
AM detector circuit or FM detector circuit respectively.
Q302
RF SW
BPF
Q303
RF BPF
Q351
RF BPF
BPF
Q401
BPF BPF
RF
Q451
BPF RF BPF
4 - 2
0.495 MHz 75.995 MHz
RF signals
D301,
D306
76.0 MHz 299.995 MHz
RF signals
230.0 MHz 629.995 MHz
RF signals
630.0 MHz 999.990 MHz
RF signals
"AGC" signal from
the AF unit (Q202, pin 4)