Icom IC-R3 detailed description of the device

IC-R3 CIRCUIT DESCRIPTION

1

1 RECEIVER CIRCUITS

1-1 RF SWITCHING CIRCUIT (RF UNIT)

(1) Below 1150 MHz

The RF signals from the antenna connector pass through
the band switching diode (D2) and an attenuator (D12, D13).
The signals are then applied to the RF circuit which sup­press out-of-band signals via the band switching circuit
(D911).

(2) Above 1150 MHz

The RF signals from the antenna connector pass through
the limitter (D1), the band switching diode (D909) and the
high-pass filter (C932–C936, C963, C964, L911, L912,
L914). The filtered signals are applied to the AF amplifier
(IC14, pin 1), and are then applied to the convertor circuit
(IC13, pin 1). The convertor circuit mixes with “CONLO” sig­nal from [CONV VCO] circuit to down convert above 1150
MHz RF signal to below 1150 MHz RF signal. The convert­ed signals output IC13 (pin 6), and are then applied to the
RF circuit which suppress out-of-band signals.

1-2 RF CIRCUIT (RF AND RF-B UNITS)

The RF circuit amplifies the received signals within the
range of frequency coverage and filters out-of-band signals.

(1) 0.495 MHz–29.995 MHz

RF signals (0.495MHz–29.995MHz) from the RF switching
circuit pass through a low-pass filter (C321–C325, L81,
L82). The filtered signals are amplified at an RF amplifier
(Q3) passing through each low-pass, bandpass, high-pass
filter depending on the receiving frequency. The amplified
signals are then applied to the 1st mixer circuit (IC1) via the
band switching diode (D10).

The signals below 1.9 MHz pass through a low-pass filter
(C344–C347, L89, L90) via the band switching diode (D4),
and are then applied to the RF amplifier circuit (Q3) via the
band switching diode (D7).

The 1.9 MHz–14.995 MHz signals pass through the band
switching diode (D5) and bandpass filter (C332–C341,
L85–L88), and are then applied to the RF amplifier circuit
(Q3) via the band switching diode (D8).

The 15 MHz–29.995 MHz signals pass through the band
switching diode (D6) and high-pass filter (C326–C330, L83,
L84) and are then applied to the RF amplifier circuit (Q3) via
the band switching diode (D9).

(2) 30 MHz–224.995 MHz (RF-B UNIT)

RF signals (30 MHz–64.995 MHz, 65 MHz–107.995.995
MHz, 108 MHz–173.995 MHz, 174 MHz–224.995 MHz)
from the RF switching diode (RF unit;D11) are passed
through low-pass filter (RF unit; C12–C17, L57–L59). The fil­tered signals pass through the each bandpass filters and the
RF amplifier depending on the receiving frequency. The fil­tered signals are then applied to the 1st mixer circuit (RF
unit;IC1).

The 30 MHz–64.995 MHz signals pass through the band
switching diode (D403) and bandpass filter (D401), and are
then amplified at the RF amplifier (Q401). The amplified sig­nal passes the bandpass filters (D402) and the band switch­ing diode (D404).

RF CIRCUIT

ANT

ANT
SW

D909, D912

"CONLO" signal from
the CONV VCO circuit

ANT
SW

D2, D911

IC13

Below 1150 MHz
RF signals

Above 1150 MHz
RF signals

LPFLPF

ANT
SW

BPF

RF

D4—D9

ANT
SW

D3, D10

0.495—30 MHz

30—225 MHz

330—470 MHz

470—800 MHz

225—330 MHz,
800—1150 MHz

Q3

LPF

ANT
SW

BPF BPF

RF

D403, D404
D503, D504
D603, D604
D703, D704

ANT
SW

D11

Q401, Q501,
Q601, Q701

BPF BPF

RF

ANT
SW

D21, D24

Q7

BPF BPF

RF

ANT
SW

ANT
SW

D803, D804
D853, D854

D805

Q801, Q851

LPF

BPF

RF

ANT
SW

D33, D35, D36

Q8, Q9

1st LO

IC1

D902

D1

to the FM-TV circuit

to the 2nd mixer circuit

FM-TV UNIT

RF-B UNIT

2

The 65 MHz–107.995 MHz signals pass through the band
switching diode (D503) and bandpass filter (D501), and are
then amplified at the RF amplifier (Q501). The amplified sig­nal passes the bandpass filters (D502) and the band switch­ing diode (D504).
The 108 MHz–173.995 MHz signals pass through the band
switching diode (D603) and bandpass filter (D601), and are
then amplified at the RF amplifier (Q601). The amplified sig­nal passes the bandpass filters (D602) and the band switch­ing diode (D604).

The 174 MHz–224.995 MHz signals pass through the band
switching diode (D703) and bandpass filter (D701), and are
then amplified at the RF amplifier (Q701). The amplified sig­nal passes the bandpass filters (D702) and the band switch­ing diode (D704).

(3) 330 MHz–469.995 MHz

RF signals (330MHz–469.995MHz) from the RF switching
circuit pass through the band switching circuit (D21) and a
bandpass filter (C19–C27, L2–L5, L39). The filtered signals
are amplified at an RF amplifier (Q7), and then passing
through the bandpass filter (D22, D23). The filtered signals
are then applied to the 1st mixer circuit (IC1) via the band
switching diode (D24).

(4) 470 MHz–799.995 MHz

RF signals (470MHz–799.995MHz) from the RF switching
circuit pass through the band switching circuit (D805) and a
low-pass filter (C321–C325, L81, L82). The filtered signals
are passing through each bandpass filters and the RF ampli­fier depending on the receiving frequency. The amplified sig­nals are then applied to the 1st mixer circuit (IC1) via the
band switching diode (D804 or D854).

The 470 MHz–599.995 MHz signals pass through the band
switching diode (D803) and bandpass filter (D801), and are
then amplified at the RF amplifier (Q801). The amplified sig­nal passes the bandpass filters (D802) and the band switch­ing diode (D804).

The 600 MHz–799.995 MHz signals pass through the band
switching diode (D853) and bandpass filter (D851), and are
then amplified at the RF amplifier (Q851). The amplified sig­nal passes the bandpass filters (D852) and the band switch­ing diode (D854).

(5) 225 MHz–329.995 MHz AND 800 MHz–1149.995 MHz

RF signals (225MHz–329.995MHz and 800MHz–1149.995
MHz) from the RF switching circuit pass through the band
switching circuit (D33). Thesignals are passing through each
bandpass filters and the RF amplifier depending on the
receiving frequency. The amplified signals are then applied
to the 1st mixer circuit (IC1) via the band switching diode
(D35 or D36).

The 225 MHz–329.995 MHz signals pass through the band­pass filter (C40–C43, C395, C396,L58, L59), and are then
amplified at the RF amplifier (Q9). The amplified signal
passes the band switching diode (D35).

The 800 MHz–1149.995 MHz signals pass through the
bandpass filter (C46–C49, C51–C54, L11–L14), and are
then amplified at the RF amplifier (Q8). The amplified signal
passes the band switching diode (D36).

1-3 1ST MIXER CIRCUIT (RF UNIT)

The 1st mixer circuit converts the received RF signals to a
fixed frequency of the 1st IF signal with a PLL output fre­quency. By changing the PLL frequency, only the desired
frequency will pass through the bandpass filters at the next
stage of the 1st mixer.

The each filtered or amplified RF signals are mixed with 1st
LO signals at the 1st mixer circuit (IC1) to produce each 1st
IF signals depending on the receiving frequency. The 1st IF
signal is output from pin 6, and passed through the band­pass filter (FI904) to suppress unwanted harmonic compo­nents. The filtered 1st IF signal is applied to the 2nd mixer
circuit.

*

1

30–799.995 MHz and 1321–2099.995 MHz range

*

2

800–1320.995 MHz and 2100–2450.095 MHz range

The 1st LO signals are generated at the 1st VCO (VCO unit;
Q22, Q23, D62) and are applied to the 1st mixer (IC1, pin 3)
directly or passing through the doubler circuit (Q26) after
being amplified at the buffer amplifiers (VCO unit; IC4).

1ST IF

FM, AM, WFM

240.1MHz

C3F (TV)

241.85*

1

, 238.35*2 MHz

1ST MIXER CIRCUIT (RF UNIT)

"RFO" signals from
the each front-end circuit

"1stVCO" signal from
the 1st VCO circuit (VCO unit)

"R3V" signal from
the LOGIC unit

"1stIF" signal to
the 2nd mixer circuit

"1stIF" signal to
the FM-TV unit

1st mixer IC (IC1)

C153

R255

R256

R257

1

2

3

6

5

4

C152

C70

C234

3

1-4 1ST IF AND 2ND MIXER CIRCUITS (RF UNIT)

The 2nd mixer circuit converts the 1st IF signal to a 2nd IF
signal.

The filtered each 1st IF signal from the bandpass filter are
mixed with the 2nd LO signal at the 2nd mixer circuit (IC10,
pin 1) to produce each 2nd IF signal depending on the
receiving frequency.

In AM and FM mode, the 2nd IF signals (26.5 MHz) pass
through the band switching diode (D71) and the bandpass
filter (FI3). The filtered signals are then amplified at the 2nd
IF amplifier (Q41), and are applied to the demodulator cir­cuit.

In WFM mode, the 2nd IF signal (13.25 MHz) passes
through the band switching diode (D72) and the bandpass
filter (FI4). The filtered signal is then amplified at the 2nd IF
amplifier (Q41), and is applied to the demodulator circuit.
In TV mode, the 2nd IF signal (58.75 MHz) passes through
the band switching diode (D901), is then applied to the 2nd
IF amplifier (Q901). The amplified signal passes through the
bandpass filter (FI901), and is applied to the demodulator
circuit.

1-5 DEMODULATOR CIRCUITS (RF UNIT)

The demodulator circuit converts the 2nd IF signal into AF
signals or video signals.

(1) AM, FM AND WFM MODE

The each 2nd IF signals from the 2nd IF amplifier (Q41) are
applied to the 3rd mixer section of the FM IF IC (IC2, pin 16)
and are then mixed with the 3rd LO signal for conversion
into a 450 kHz 3rd IF signal.

IC2 contains the 3rd mixer, limiter amplifier, quadrature
detector and S-meter detector, etc. A frequency from the
PLL reference oscillator (VCO unit; IC3) is used for the 3rd
LO signal (12.80 MHz).

• AM MODE

The 3rd IF signal is output from FM IF IC (IC2, pin 3) and
passes through the ceramic bandpass filter (FI2). The fil­tered IF signal is applied to the AM detector circuit (Q44,
Q45) to converted into AF signals, and the signals are
applied to the AF circuit (LOGIC unit).

• FM MODE

The 3rd IF signal is output from FM IF IC (IC2, pin 3) and
passes through the ceramic bandpass filter (FI2). The fil­tered signal is fed back and amplified at the limiter amplifier
section (pin 5), then demodulated AF signals at the quadra­ture detector section (pins 10, 11) and detector coil (L21).
The demodulated AF signals are output from pin 9 and are
applied to the AF circuit (LOGIC unit).

• WFM MODE

The 3rd IF signal from the 3rd mixer bypasses the ceramic
filter (FI2) and fed back to the limiter amplifier section (pin 5).
The amplified signal is demodulated at the quadrature
detector section (pins 10, 11) and detector coil (L21). The AF
signals are output from pin 9 and are applied to the AF cir­cuit (LOGIC unit).

By connecting R55 to R54 in parallel, the output character­istics of pin 12, “RSSI”, change gradually. Therefore, the FM
IF IC can detect WFM components.

2ND IF AND DEMODULATOR CIRCUITS (RF UNIT)

Mixer

16

Limiter
amp.

2nd IF filter

450 kHz

RSSI

IC2 TA31136FN

13

2nd IF signal from the
IF amplifier (RF unit; Q41)

"RSSI" signal to the CPU
(Logic unit; IC11, pin 7)

11109

875 32

Active
filter

FI2

Noise

detector

FM

detector

Noise
comp.

"SDET" signal to the CPU
(Logic unit; IC11, pin 12)

12

C106

C108 C109

C111

R61

R59

R60

WFM

RX

"FMAF" or "AMAF" signal
to the AM/FM switch circuit
(LOGIC unit; D15, D18)

2nd

Q42

"2nd LO" signal from
IC3, pin 2 (VCO unit)

C112

R57

C992

R54

R55

2

Q121

D121

D122

C114

C115

D75 D76

R84

R56

C113

L21