Icom IC-RX7 Service Manual Addendum - Section 4. Circuit
4 - 1
RF AMP/FILTER CIRCUITS (1 GHz BAND)
The 833–1300 MHz RX signals are passed through the
diode SW (D10) and HPF/LPF for unwanted signal removal,
and applied to the RF AMP (Q6, D22, 23).
The amplified RX signals are applied to the wide band RF
AMP (IC1) via the diode SW (D42).
REGULATOR SWs
The power supply for each RF circuit (3V) is switched by
Q11, 17, 18 and 19.
1st MIXER and 2nd MIXER
The RX signals from each RF circuit are amplified by the
wideband RF AMP (IC1) and passed through the attenuator,
then applied to the 1st mixer (IC5). The RX signals are
mixed with the 1st LO signals from the 1st VCO UNIT to be
converted into the 429.1 MHz 1st IF signal.
The 429.1 MHz 1st IF signal is filtered by the 1st IF filter (FI1)
to remove unwanted signals, then applied to the 2nd mixer (IC8).
The 2nd IF signal is mixed with 2nd LO signals from the 2nd
VCO UNIT to be converted into the 2nd IF signal; 19.65 MHz
for AM/FM mode, 20.75 MHz for WFM mode.
In AM/FM mode operation, the 2nd IF signal is filtered by
the 2nd IF filter (FI2) to remove unwanted signals, then
applied to the 2nd IF AMP (Q31).
In WFM mode operation, the 2nd IF signal is by-passed the
2nd IF filter (FI2).
The path of 1st IF signal is switched by diode SWs (D44, 49).
3rd IF, DEMODULATOR and AGC CIRCUITS
The 2nd IF signal from the 2nd IF AMP (Q11) is applied
to IC13. IC is the IF IC which contains mixer, limiter,
quadrature detector and RSSI circuit in its package.
The 2nd IF signal is mixed with the 3rd LO signal from the LO
AMP (Q36) to be converted into the 3rd IF signal; 450 kHz for
AM/FM mode, 1.55 MHz for WFM mode.
• AM/FM MODE
The 3rd IF signal is filtered by the 3rd IF filter (FI3) to
remove unwanted signals, and applied to the each detector
circuit (AM or FM detector).
• WFM MODE
The 3rd IF signal is by-passed FI3, and applied to the FM
demodulator circuit. The path of 3rd IF signal is switched by
diode SWs (D47, 48) controlled by Q37.
In FM mode operation, the 3rd IF signal (450 kHz) is
FM-demodulated by the ceramic discriminator (X3).
In WFM mode operation, the 3rd IF signal (1.55 MHz) is
FM-demodulated by the LC resonator for WFM demodulation.
The switching of mode (WFM) is controlled by Q38, 40.
• AM MODE
The 3rd IF signal is amplified by Q26 and AM-demodulated
by Q25.
In each mode, the detected DC components are feedback
4-1 MAIN UNIT
MAIN UNIT has RF circuits, 1st and 2nd IF circuits, FM and
AM demodulator circuits. The RX signals from the antenna
are fi ltered, amplifi ed and converted into the 1st and 2nd IF
signals in sequence, then FM/AM-demodulated.
ATTENUATOR CIRCUIT
RF signals from the antenna are passed through the limiter
(D1) and ATT SW (D2), then applied to the band SWs which
select the appropriate bandpass/low-pass filter according to
the RX frequency.
When the attenuator is inactivated, Q2 is OFF and the RX
signals are passed through D2. When the attenuator is
activated, Q2 is ON and the RX signals are passed through
the attenuator for 20 dB attenuation. The switching of Q2
and D2 is carried out by Q3 with the control signal "ATT."
RF AMP/FILTER CIRCUITS (BC/HF BAND)
The 0.15–76 MHz RX signals are passed through the diode
SW (D4) and LPF for unwanted signal removal and diode
SW (D28), then applied to the RF AMP (Q12, D33, 34).
When the “external antenna” is selected for AM broadcast
RX, the 0.5–3 MHz RX signals are passed through the
diode SW (D5) and the BPF (D53, etc.), then applied to the
RF AMP (Q12, D33, 34) via the diode SW (D29).
When the “internal bar antenna” is selected, the 0.5–1.6
MHz RX signal is passed through the diode SW (D27) and
applied to the RF AMP (Q12, D33, 34) via the diode SW
(D29).
The amplified RX signals from the RF AMP (Q12, D33, 34)
are applied to the wide band RF AMP (IC1) via the diode
SW (D37).
RF AMP/ FILTER CIRCUITS (VHF BAND)
The 76–350 MHz RX signals are passed through the diode
SW (D7) and HPF/LPF (D57, etc.) for unwanted signal
removal, and applied to the RF AMP (Q7, D14, 15).
The amplified RX signals are passed through the tuned BPF
(D31, 35, 58, etc.) for unwanted signal removal, and applied
to the wide band RF AMP (IC1) via the diode SW (D38).
When the RX frequency is 160 MHz and higher, the center
frequency of BPF is shifted to higher by D51 and D52.
RF AMP/FILTER CIRCUITS (UHF BAND)
The 350–470 MHz RX signals are passed through the diode
SW (D8) and HPF/LPF for unwanted signal removal, and
applied to the RF AMP (Q41, 42, D18, 19).
The amplified RX signals are passed through the tuned BPF
(D32, 36, etc.) for unwanted signal removal, and applied to
the wide band RF AMP (IC1) via the diode SW (D40).
RF AMP/FILTER CIRCUITS (800 MHz BAND)
The 470–833 MHz RX signals are passed through the diode
SW (D9) and tuned BPF (D12, 13, etc.) for unwanted signal
removal, and applied to the RF AMP (Q5, D20, 21).
The amplified RX signals are passed through the tuned BPF
(D25, 26, etc.) for unwanted signal removal, and applied to
the wide band RF AMP (IC1) via the diode SW (D41)