Icom IC-R10 User manual

o
ICOM
SERVICE
MANUAL

INTRODUCTION
This service manual describes the latest information for the IC-R10 at the tinrre of
publication.
MODEL VERSION SYMBOL
U.S.A. USA
IC-H10 France FRA
U,K, UK
Europe EUR
DANGER
NEVER connect the receiver to an AC outfet or to aDC power supply that uses
more than 16 V. Such aconnection could cause afire hazard and/or electric
shock.
DO NOT expose the receiver to rain, snow or any liquids.
DO NOT reverse the polarities of the power supply when connecting the
receiver.
DO NOT apply an RF signai ol more than 20 dBm (100 mW) to the antenna
connector. This could damage the receiver's front end,
ORDERING PARTS
Be sure to include the following four points when ordering replacement parts:
1. 10-digit order numbers
2. Component pari number and name
3. Equipment model name and unit name
A. Quantity required
^SAMPLE ORDER>
1110001310 S.IC TA7363F IC-RIO MAIN UNIT Ipiece
3310009560 Screw FHM2x6ZK(BT} IC-RlO CHASSIS 7pieces
Addresses are provided or> the inside back cover for your convenience.
REPAIR NOTES
1.Make sure aproblem is internal before disassembling the receiver.
2. DO NOT open the receiver until the receiver is discormected from its power
source.
3. DO NOT force any of the variable components. Turn them slowly and
smoothly.
4. DO NOT short any circuits or electronic parts. An insulated tuning tool MUST
be used for all adjustments.
5. DO NOT keep power ON for along time when the receiver is defective.
6. READ the instructions of test equipment thoroughly before connecting
equipment to the receiver.
I

TABLE OF CONTENTS
SECTION 1SPECIFICATIONS
SECTION 2INSIDE VIEWS
SECTION 3DISASSEMBLY INSTRUCTIONS
SECTION 4CIRCUIT DESCRIPTION
4-1RECEIVER CIRCUITS 4-1
4-2 PLL CIRCUITS 4-4
4-3POWER SUPPLY CIRCUITS 4-5
4-4CPU PORT ALLOCATIONS 4-6
SECTION 5ADJUSTMENT PROCEDURES
5-1 PLL AND BFO ADJUSTMENT 5-1
5-2COMMAND ADJUSTMENT (ADJUSTMENT SET MODE) 5-3
SECTION 6PARTS LIST
SECTION 7MECHANICAL PARTS AND DISASSEMBLY
SECTION 8SEMI-CONDUCTOR INFORMATION
SECTION 9BOARD LAYOUTS
SECTION 10 BLOCK DIAGRAM
SECTION 11 VOLTAGE DIAGRAM

SECTION 1SPECIFICATIONS
GENERAL
•Frequency range
•Mode
•Tuning steps
•Power supply requirement
•Current drain (at 13.5 VDC)
•Usable temperature range
•Antenna connector
•Scan speed
•Cl-V connector
•Dimensions (projections not included)
•Weight
RECEIVER
•Receive system
•Intermediate freq.
•Sensitivity
(typical, except spurious points)
•Squelch sensitivity (at threshold)
•Selectivity
•Audio output power (at 13.5 VDC)
•External speaker connector
VERSION FREQUENCY RANGE
Europe, U.K. 500 kHz-1 300 MHz
France 500 kHz-87.5 MHz
108 MHz-1300 MHz
U.S.A.
500 kHz-823.9999 MHz
849.0001-
868.9999 MHz
894.0001-
1300 MHz
:FM, WFM, AM, USB, LSB, CW
:0.1, 0.5, 1,5, 6.25, 8, 9, 10, 12.5, 15, 20, 25, 30, 50, 100 kHz or
user-programmable (0.1-999.9 kHz/0.1 kHz steps)
4.8 VDC (4 AA (R6) Ni-Cd cells); or, 4.8-1 6VDC acceptable (negative ground)
Rated audio 180 mA typ.
Standby 110 mA typ.
Power saved 38 mA typ.
-10°C to +50°C; +14“F to +122T
BNC (50 Q)
16.7 ch/sec. (programmed scan), 6.25 ch/sec. (memory scan)
3-conductor 3.5 (d) mm (Vs")
58.5 (W) X130 (H) X31 .3 (D) mm; 2.3 (W) x5.1 (H) x1-2 (D) in
310 g; 10.9 oz.
Triple-conversion superheterodyne
1St 266.7 MHz (340.0000-999.9999 MHz)
429.1 MHz (except above freq.)
2nd 10.7 MHz
3rd 455 kHz
FREQUENCY (MHz) FM AM SSB/CW
0.5 -4.9999 —1.6 pV 0.40 pV
5.0 -74.9999 0.32 pV —1.0 pV 0.25 pV
75.0- 199.9999 1.0 pV
200.0 -339.9999 0.45 pV 2.2 pV 1.6 pV 0.40 pV
340.0 -699.9999 0.35 pV 1.3 pV 1.4 pV 0.32 pV
700.0 -799.9999 0.79 pV 2.0 pV 2.0 pV 0.63 pV
800.0 -899.9999 1.6 pV 0.40 pV
900.0 -1300.0000 —
*FM and WFM are measured at 12 dB SINAD; AM, SSB and CW are measured at 10 dB S/N.
FREQUENCY (MHz) FM WFM AM
0.5 -4.9999 0.50 pV —1.6 pV
5.0 -74.9999 0.32 pV —1.0 pV
75.0- 199.9999 1.0 pV
200.0 -339.9999 0.45 pV 2.2 pV
340.0- 699.9999 0.35 pV 1.3 pV EDH
700.0 -799.9999 2.0 pV
800.0 -899.9999 1.6 pV
900.0 -1300.0000 —
SSB, CW More than 4kHz /6 dB
AM, FM More than 15 kHz/6 dB
WFM More than 150 kHz/6 dB
More than 120 mW at 10% distortion with an 8Qload
3-conductor 3.5 (d) mm (V8")/8 Q
1-
1

3rd IF arnplilier
qirculi
2nci IF amplifier
(Q2i'2SCJ2i&
tMam band]
IF 1C (Sub-bandi -
(,tC47l ;TA31 136F)
Top view
SSB detector circuit
BFO ampliJier (Q95t:2SC42ltj
2nd IF amplifier (Q42l :2SC42V5
Sub-band)
3rd IF circuit (SSB/CW)
3fd tF circuit (AM /FM)
2id IF circuit (WFM]
AF amplifier (IC361 :TA73eaF)
IF 1C
(IC?1 :TA3i 136F /Mam band)
AF sv/ilch (IC301 :BU4066CFV)
2nd miJter
(Q41 1 : 2SC50&5 /Sub-band)
DATA expander 1C
(IC3D5: BU4094BF)
2nd mixer 1C
(I Cl 1: ^lPC27ST /Main band)
2nd PLL 1C (I C50 1:MP03 14063)
VXO circuit
2nd refatenca oscillaior
Bottom view (x&d icr-sss n2,e mhz)
RF amplifier
(Q5l:2SC42i5> —
1sl miser IC —
^
(IC271; MPC276T)
RF circuit —=
(700 MHz -1.30D MHz)
RF circuit
(300 MHz '500 MHZ)“
RF circuit ——
—
(30 MHz -75 MHi)
RF circuit —
-
[O.&MHZ' 1.9 MHz}
RF circuit
{15 MHz -3D MHZ)
iStlFcircuH ——
”
{340 MHz '1GHz)
Tw/^
r
Reference cscillaior.
{X501; 10,345 MHz)
Top view
4-
RF circuit
<500 MHZ -700 MHz)
RF circuit
<75 MRz -300 MHz)
RF circuit
<1.9 MHZ -15 MHz)
tsMF amphlier (Q421;2SC4226)
1st IF circuit
(0.5 MHz -340 MHz and
1GHz -1.3 GHz}
1st VCO unit
Bottom view
•LOGIC unit
Bottom view
AF mute switch
flC950: TC43D6F)
CPU IC
(IC1: pP07B054GK]
VSC fC
(IC201: MPC5D23-115)
AF amplifier
(0950: 3SC4211)
BFO Circuit
2-1

SECTION 3DISASSEMBLY INSTRUCTIONS
•Opening the case
®Remove the SP cap, O-
@Unscrew 6screws, Oand 0to open the case.
•Removing the LOGiC unit
®Unplug J1 to separate the front panel and rear panel.
@Unsolder 2points Oand unscrew 4 screws 0.
(D Remove the LOGIC unit in the direction of the arrow.
iJ^Be careful when pulling, pull up, LCD components are
on the opposite side.
•Removing the MAiN unit
®Unscrew 3screws ©.
(D Remove the MAIN unit in the direction of the arrow.
•Removing the RF unit
®Remove 3knobs Oand unscrew 3nuts 0.
@Unsolder 4points 0and unscrew 3screws ®.
@Remove the RF unit in the direction of the arrow.
Note
•)KWhen pulling the terminals, the ©side of each
terminals has apiece of rubber affixed.
3-1

4-1 RECEIVER CIRCUITS
4-1-1 ANTENNA SWITCHING CIRCUIT (RF UNIT)
Received signals enter the RF unit from the antenna
connector (J1) and pass through alimiter (D1) and an
attenuator circuit (D2). The signals are then applied to the
RF circuit via the antenna switching circuit (D51, D151,
D171, D211, D231) which suppress out-of-band signals.
4-1-2 RF CIRCUIT (RF UNIT)
The RF circuit amplifies the received signals within the
range of frequency coverage and filters out-of-band signals.
(1)
0.5 MHz-74.9999 MHz signals
RF signals (0.5 MHz-74.9999 MHz) from an antenna
switching circuit (D51) pass through alow-pass filter (L51,
L52). The filtered signals are amplified at an RF amplifier
(Q51) through each bandpass filter depending on the
receiving frequency. The amplified signals are then applied
to the 1st mixer circuit (IC271) through the band switching
diode (D253).
The signals below 1.9 MHz pass through alow-pass filter
(L55, L56) via the band switching diode (D52), and are then
applied to the RF amplifier circuit (Q51) via the band
switching diode (D53).
The 1.9 MHz-29.9999 MHz signals pass through the band
switching diode (D61) and low-pass filter (L61, L62). The 1.9
MHz-14.9999 MHz signals pass through the band switching
diode (D81) and bandpass filter (L82, L83, L91, L92), and
are then applied to the RF amplifier circuit (Q51) via the
band switching diode (D82).
The 15.0 MHz-29.9999 MHz signals pass through the band
switching diode (D101) and high-pass filter (LI 02, LI 03)
and are then applied to the RF amplifier circuit (Q51) via the
band switching diode (D102).
•RF filters
Receive frequency
[MHz] sw diodes BPF select
signal Components
0.5- 1.8999 D52, 053 80 L55, L56
1.9-14.9999 D81 ,082 81 L82, L83, L91, L92
15.0-29.9999 0101, 0102 82 L102, LI 03
30.0 -74.9999 0121, 0122 83 L122, L123
The 30,0 MHz-74.9999 MHz signals pass through the band
switching diode (D121) and high-pass filter (LI 22, LI 23),
and are then applied to the RF amplifier circuit (Q51) via the
band switching diode (D122).
(2) 75.0 MHz-199.9999 MHz
The 75.0 MHz-199.9999 MHz signals pass through the
tunable bandpass filter (D152, LI 52) via the band switching
diode (D151), and are then amplified at the RF amplifier
(Q151) and pass through another tunable bandpass filter
(D153, LI 55). The filtered signals are applied to the 1st
mixer circuit (IC271) via the band switching diode (D154).
(3) 200.0 MHz-499.9999 MHz
The 200.0 MHz-499.9999 MHz signals pass through the
tunable bandpass filter (D172, LI 72) via the band switching
diode (D171), and are then amplified at the RF amplifier
(Q171) and pass through another tunable bandpass filter
(D173, LI 75). The filtered signals are applied to the 1st
mixer circuit (IC271)via the band switching diode (D1 74).
(4) 500.0 MHz-699.9999 MHz
The 500.0 MHz-699.9999 MHz signals pass through a
tunable band pass filter (D213, L213, L214) via the band
switching diode (D211), and are then amplified at an RF
amplifier (Q211) and pass through another tunable
bandpass filter (D214, L216, L217). The filtered signals are
applied to the 1st mixer circuit (IC271) via the band
switching diode (D154).
(5) 700.0 MHz-1300.0000 MHz
The 700.0 MHz-1300 MHz signals pass through ahigh-
pass filter (L232, L233) via the band switching diode (D231),
and are then amplified at the RF amplifier (Q231) and pass
through atunable bandpass filter (D238, L240). The filtered
signals are applied to the 1st mixer circuit (IC271) via the
band switching diode (D236).
•Tunable band pass filters and RF amplifiers
Receive frequency
[MHz] .
BPF select
signal
Varactor
diodes RF amplifier
84 0152, 0153 Q151
200.0- 499.9999 85 0172, 0173 Q171
500.0- 699.9999 86 0213, 0214 Q211
700.0- 1300.0000 87 0238 Q231
RF filter and amplifier circuits

D152, D153, D172, D173, D213, D214 and D238 employ
varactor diodes that are controlled by the CPU (LOGIC unit;
IC1 )to track the bandpass filter. These varactor diodes tune
the center frequency of an RF passband for wide width
receiving and good image response rejection.
4-1-3 1ST MIXER AND 1ST IF CIRCUITS {RF UNIT)
The 1st mixer circuit converts the received RF signals to a
fixed frequency of the 1st IF signal with the PLL output
frequency. By changing the PLL frequency, only the desired
frequency will pass through the band pass filters at the next
stage of the 1st mixer.
The amplified signals are mixed with 1st LO signals from the
1st VCO unit at a1st mixer (IC271) to produce 1st IF signals
(266.7 MHz; 340.0 MHz-999.9999 MHz, 429.1 MHz; 0.5
MHz-339.9999 MHz and 1.0 GHz-1 .3 GHz).
The 1st IF signals are applied to each IF filter (FI401 for
266.7 MHz IF signal, FI411 for 429.1 MHz IF signal) to
suppress out-of-band signals. The 1st IF signals are
amplified at the 1st IF amplifier (Q421) and then applied to
the 2nd mixer on the MAIN unit.
•1st LO frequency and 1st IF frequency
Receive frequency
[MHz]
1st LO frequency
[MHz]
1st IF frequency
[MHz]
0.5- 339.9999 429.6 -769.0999 429.1
340.0- 609.9999 606.7 -876.6999 266.7
610.0- 999.9999 343.3 -733.2999 266.7
1000.0- 1300.0000 733.3 -870.9000 429.1
4-1-4 2ND MIXER AND 2ND IF CIRCUIT
(MAIN UNIT)
The 2nd mixer circuit converts the 1st IF signal to a2nd IF
signal.
The 1st IF signals (266.7 MHz or 429.1 MHz) from the RF
unit are applied to the 2nd mixer circuit (IC11) for mixing
with the 2nd LO signals to be converted into a10.7 MHz
2nd IF signal. The 2nd IF signal is applied to the IF filter
(Fill) to suppress out-of-band signals, and is then amplified
at the 2nd IF amplifier (Q21 ).
4-1-5 3RD IF AND DEMODULATOR CIRCUIT
(MAIN UNIT)
The 3rd mixer circuit converts the 2nd IF signal to a3rd IF
signal.
IC71 contains the 3rd mixer, limiter amplifier, quadrature
detector, s-meter detector and noise detector circuits.
The 2nd IF signal (10.7 MHz) from the 2nd IF amplifier
(Q21) is applied to the 3rd mixer section of IF 1C (IC71, pin
16) and is then mixed with a10.245 MHz 3rd LO signal
generated by X501 on the RF unit for conversion to a455
kHz 3rd IF signal. The 3rd IF signal is demodulated at each
demodulator circuit.
(1)
FM
The 3rd IF signal from the 3rd mixer (1071, pin 3) passes
through the ceramic filter (FI111) to suppress unwanted
heterodyned frequency signals. It is fed back to 1071, then
amplified at the limiter amplifier section (pin 5) and applied
to the quadrature detector section (pin 10) to demodulate
the 3rd IF signal into AF signals. The AF signals are output
from pin 9and passed through the de-emphasis circuit
(R79, 086) with frequency characteristics of -6 dB/octave,
and then applied to the AF switch (10301 c, pin 4).
Aportion of the AF signals from pin 9(1071) passes through
the low-pass filter (R78, 084) and is applied to the OPU
(LOGIO unit; 101) as AFO control signals.
(2) WFM
The signal from the 3rd mixer is applied to the limiter
amplifier section (1071, pin 5). The amplified signals are
demodulated at the quadrature detector section (1071, pin
5). The AF signals are output from pin 9(1071) and are
applied to the AF switch (10301c, pin 4) the same as in FM
mode.
By connecting R81 to R72 in parallel, the output
characterstics of pin 12, “RSSI”, change gradually.
Therefore, the FM IF 10 can detect WFM components.
(3) AM
The signal from the 3rd mixer passes through the ceramic
filter (FI111) and is amplified at the 3rd IF amplifiers (Q151,
Q161). The amplified signal is demodulated at the AM
detector (Q171). The demodulated AF signals are applied to
the AF switch (10301 d, pin 8) via the ANL control circuit
(Q172).
•2nd IF, 3rd IF and demodulator circuit
IC71
to AF switch
IC301
4-2

(4) SSB/CW
The signal from the 3rd mixer passes through the ceramic
filter (FI101) and is amplified at the 3rd IF amplifiers (Q151,
Q161) and buffer amplifier (Q201). The amplified signals
are applied to the SSB/CW detector (D201 ,D202) and
mixed with BFO signals from the BFO circuit (LOGIC unit;
X231) via the BFO amplifier (0951) to demodulate AF
signals. The demodulated AF signals are applied to the AF
switch (IC301b, pin 11) after being pre-amplified at the AF
pre-amplifier (0202).
•Bandpass filter selection
Mode(s) Bandpass filter(s) Passband width
NFM /AM FI111 15 kHz
SSB /CW FI101 4kHz
WFM ——
4-1-6 SUB-BAND RECEIVER CIRCUIT (MAIN UNIT)
The sub-band receiver circuit is employed by the band
scope and SIGNAVI functions.
Aportion of the 1st IF signals from the RF unit is mixed with
the sub 2nd LO signals at the 2nd mixer circuit (0411) to be
converted into 455 kHz sub 2nd IF signal. The 2nd IF signal
Is applied to the IF 1C (IC471 ,pin 5) via the IF filter (FI411)
and 2nd IF amplifier (0421). The IF 1C (IC471) outputs
signals to lead the CPU (LOGIC unit; IC1) under conditions
of RSSI or noise squelch.
4-1-8 SQUELCH CIRCUIT (MAIN UNIT)
Anoise squelch circuit cuts out AF signals when no RF
signal is received. By detecting noise components in the AF
signals, the CPU switches the AF mute switch.
Some of the noise components in the AF signals from IC71
(pin 9) are passed through the active filter (IC71 ,pins 8, 7),
and then applied to the noise detector section. The squelch
control pot (RF unit; R11) adjusts the input level of the
active filter, and the level is used for the squelch threshold
reference. The detected noise signals are applied to the
CPU (LOGIC unit; IC1, pin 65) via the “SQL” line. The CPU
then analyzes the noise condition and controls the “MUTE”
port to cut off the AF signal using the AF mute switch
(LOGIC unit; IC950).
4-1-9 VSC CIRCUIT (LOGIC UNIT)
The VSC (Voice Scan Control) detects AF signals and
mutes undesired signals such as unmodulated, beat and
noise component signals. When the VSC function is ON
and an unmodulated signal is received, squelch functions
the same as closed (no signal condition) even when it’s
open, or the scan function resumes for ashort period on
any scan setting during scanning.
Aportion of the AF signals from the low-pass filter (Q950) is
applied to the VSC control circuit (IC201) to detect
demodulated signals while the VSC function is ON. When
audio component signals are included in the AF signals, the
VSC 1C (IC201 )outputs alow level signal from pin 13 to the
CPU (IC1 ,pin 1)to release the mute switch (IC950).
4-1-7 AF AMPLIFIER CIRCUIT (MAIN UNIT)
The AF amplifier circuit amplifies the demodulated AF
signals to drive aspeaker.
The AF signals from the AF switch (IC301) are applied to
the LOGIC unit through a“DETOM” line. The AF signals are
amplified at the AF amplifier (LOGIC unit; 0950), and are
then applied to the AF mute switch (LOGIC unit; IC950).
The output signals from the AF mute switch (LOGIC unit;
IC950) are applied to the [VOL] control (RF unit; R11), and
are then power-amplified at the AF amplifier (MAIN unit;
IC361 ,pin 4) to drive aspeaker.
4-1-10 BFO CIRCUIT (LOGIC UNIT)
The BFO (Beat Frequency Oscillator) circuit consists of
X231, IC231 and D231. The oscillator provides abeat
frequency signal (USB; 456.5 kHz, LSB; 453.5 kHz) to the
SSB/CW detector circuit (MAIN unit; D201, D202) for
demodulating the 3rd IF signal into AF signals.
The oscillating frequency for each mode (LSB/USB/CW) is
switched by changing the capacitance of avaractor diode
(D231). When USB mode is selected, the CPU (IC1, pin 3)
outputs “LOW” level voltage to D231 to change the BFO
frequency to 456.5 kHz.
•Squelch and AF amplifier circuits
4-3

4-1-11 AGC CIRCUIT (MAIN UNIT)
The AGC (Auto Gain Control) circuit reduces IF/RF amplifier
gain to keep the audio output at aconstant level. The
receiver gain is determined by the voltage on the IF-AGC
line (Q182 collector) and RF-AGC line (RF unit; Q901
collector).
The 3rd IF signals from the 3rd IF amplifier (Q161) are
detected at the AM detector (Q171). Aportion of the
detected signals is applied to the AGC amplifiers (Q182 and
RF unit; Q901) as the AGC control voltage. The AM
detector (Q171) is used for the AGC detector in the AGC
circuit.
When receiving strong signals, the detected voltage
increases and the AGC voltage decreases via the AGC
amplifiers (Q182 and RF unit; Q901). As the AGC voltage is
used for the bias voltage of the IF/RF amplifiers, IF/RF
amplifier gain is decreased.
4-1-12 NOISE BLANKER CIRCUIT (MAIN UNIT)
The noise blanker circuit detects pulse-type noise, and
stops IF amplifier operation during detection.
Aportion of the 2nd IF signals from the 2nd IF amplifier for
the sub-band (Q421) is amplified at the noise amplifier
circuit (Q801, Q802). The amplified signal is recified at the
noise detector circuit (Q805) for conversion into DC voltage.
The DC voltage is applied to the NB control circuit (Q806,
Q807) to control the NB switch (Q810).
Some DC voltage is fed back to the noise amplifier circuit
(Q801 ,Q802) via the DC amplifier (Q808). The DC amplifier
functions as an AGC circuit to reduce averaged noise.
Therefore, the noise blanker function shuts off pulse-type
noise only.
4-2 PLL CIRCUITS
4-2-1 GENERAL
1ST/2ND LO PLL circuits (RF/MAIN units) provide stable
oscillation of the receive LO frequencies. The PLL circuit
consists of the PLL 1C (IC501 on the RF/MAIN units),
charge pump, loop filter and reference oscillator and
employs apulse swallow counter.
4-2-2 1ST LO PLL CIRCUIT (RF UNIT)
Signals from the 1ST VCO unit pass through the buffer
amplifier (Q551) and are prescaled in the PLL 1C (IC501,
pin 10) based on the divided ratio (N-data). The PLL 1C
detects the out-of-step phase using the reference frequency
and outputs it from pin 6. The output signal is passed
through the charge pump (Q521 ,Q522) and is applied to
the loop filter (R527, C527) to be converted into DC voltage
as aPLL lock voltage. The PLL lock voltage is applied to
the 1ST VCO unit via the VI Lline.
Aportion of the signal from the loop filter (R527, C527) is
amplified at the buffer amplifier (Q502) and is then applied
to the CPU (LOGIC unit; IC1) as the lock voltage
information (LVI). The CPU (pin 6) outputs a“TUNE” signal
based on the lock voltage; the voltage is amplified at the
buffer amplifiers (LOGIC unit; Q181, 0182) and is then
applied to the RF unit as the tunable bandpass filter control
signal (VTUNE). This signal (VTUNE) is used for the RF
tunable bandpass filters to match the filter’s center
frequency to the desired receive frequency.
4-2-3 REFERENCE OSCILLATOR CIRCUIT
(RF UNIT)
The reference oscillator circuit (X501, IC501) generates a
10.245 MHz reference frequency which is stabilized within
the temperature range -10°C (+14T) to +50°C (+122°F).
The reference frequency is applied to the PLL 1C and also
applied to the MAIN unit as the 3rd LO signal via the buffer
amplifier (0531).
4-2-4 1ST VCO CIRCUIT (1ST VCO UNIT)
The 1ST VCO circuit contains three separate VCO circuits
depending on the receive frequency. The oscillated signal at
one of the three VCO circuits is applied to the buffer
amplifier (0601). The amplified signal is applied to the RF
unit via the VI Oline and is then applied to the 1st mixer
circuit (RF unit; IC271, pin 3)as the 1st LO signal after
being amplified at the buffer amplifier (RF unit; 0552).
Aportion of the signal from the VI Oterminal (1ST VCO
unit; J601) is amplified at the buffer amplifier (0551) and is
then fed back to the PLL 1C (IC501, pin 10) as the
comparison signal.
•1st LO PLL circuit (RF unit)
4-4