Circuit Description; Receiver Circuits; Hf/50 Mhz Rf Circuit; Vhf And Uhf Rf Circuits (Pa Unit) - Icom IC-7000 Service Manual

SECTION 3

3-1 RECEIVER CIRCUITS

3-1-1 HF/50 MHz RF CIRCUIT (MAIN AND PA UNITS)
The HF/50 MHz RF filters pass only the desired band sig-
nals and suppress undesired band signals. The HF/50 MHz
RF circuit has 7 low-pass and 5 high-pass filters for speci-
fied band use.
The HF/50 MHz RF signals from the [ANT1] connector, pass
through one of 7 low-pass filters as below, the TX/RX switch
(PA unit; RL801), low-pass filter (PA unit; L801, L802, C801
–C805) and band switch (D151), and are then applied to the
MAIN unit via J101 (MAIN unit).
• Used RF low-pass fi lter (PA unit)
Frequency Control Entrance
(MHz) signal relay
0.03–2 MHz L1 RL881
2–4 MHz L2 RL921
4–8 MHz L3 RL841
8–15 MHz L4 RL901
The signals from the PA unit are applied to the RF switch
(Q101) via the band switch (D113) and then passed through
the 20 dB attenuator (D101, D102).
The signals below 1.8 MHz are passed through the low-pass
filter (L103, L104, C106, C110, C111) and then applied to
the preamplifier circuit.
The other band signals (1.8–60 MHz) are passed through
the high-pass filter (L105, L109, L110, L116, L117, C108,
C109, C114–C116) to suppress strong signals below
1.8 MHz and then applied to the low-pass and high-pass fil-
ter circuits.
(1) 1.8–2 MHz
The filtered signals from the high-pass filter are passed
through the low-pass filter (L205, L207, C209–C213) and
then applied to the preamplifier circuits.
(2) 2–30 MHz
The filtered signals from the high-pass filter are applied to
one of 5 high-pass filters as at right above after passed
through the low-pass filter (L205, L207, C209–C213) and
are then applied to the preamplifier circuit.
• RECEIVER CONSTRUCTION
PA UNIT
MAIN UNIT
[ANT1]
0.03–60 MHz
LPF
HPF
[ANT2]
60–470 MHz
LPF
BPF

CIRCUIT DESCRIPTION

Frequency Control Entrance
(MHz) signal relay
15–22 MHz L5 RL941
22–30 MHz L6 RL821
30–60 MHz L7 RL861
1st LO:
124.517 MHz–
594.587 MHz
Preamp.
FI601
Q301
Crystal
amp.
filter
1st mixer
124.487 MHz
IC401
(WFM; 134.732 MHz)
• Used RF high-pass fi lter (MAIN unit)
Frequency Control
(MHz) signal
1.8–2 MHz B1
2–3.4 MHz B2
3.4–6.9 MHz B3
6.9–13.9 MHz B4
(3) 30–60 MHz
The filtered signals from the high-pass filter are passed
through another high-pass filter (L215, L217, C228, C229,
C237, C238) and then amplified at the RF amplifier (Q211).
The amplified signals are applied to the preamplifier circuit.

3-1-2 VHF AND UHF RF CIRCUITS (PA UNIT)

The VHF and UHF RF circuits filter and amplify only the
desired band signals and suppress undesired band signals.
The both RF circuits have preamplifiers and bandpass filters.
• VHF RF CIRCUIT
The VHF RF signals from the [ANT2] connector pass
through the low-pass filters (L506, L508, L510, L601–L603,
C516, C519, C521, C601, C602) and antenna switching cir-
cuit (D507–D509). The switched signals are passed through
the attenuator (D551, D552) and bandpass filter (D553,
D554, D556). The filtered signals are applied to the pream-
plifier (Q551) and then passed through another bandpass
filter (D558–D560).
The filtered signals are passed through the band switch
(D462) and then applied to the 1st mixer circuit (MAIN unit)
via J101 (MAIN unit).
• UHF RF CIRCUIT
The UHF RF signals from the [ANT2] connector pass
through the low-pass (L601–L603, C601, C602) and high-
pass (L413, L414, C428, C429, C431, C433) filters and
then applied to the antenna switching circuit (D408–D410).
The switched signals are passed through the attenuator
(D451, D452) and then amplified at the preamplifier (Q451)
between the 2 bandpass filters (D453–D456). The filtered
signals are amplified at another preamplifier (IC471, pins 1, 4).
2nd LO:
124.032 MHz
FI901
Crystal
filter
2nd mixer
455 kHz
D801
to WFM detector
circuit (IC1401)
3 - 1
Entrance Frequency Control
diode (MHz) signal
D204 13.9–20.9 MHz B5
D205 20.9–30 MHz B6
D208 30–60 MHz B7
D209
3rd LO:
438.85 kHz
FI1101
Crystal
to DSP circuit
filter
3rd mixer
455 kHz
IC1101
Entrance
diode
D210
D211
D212