Fm-Tv Circuit - Icom IC-R3 Service Manual

An oscillated signal from the 1st VCO passes thorough the
buffer amplifiers (IC4, Q25), is applied to the PLL IC (IC3,
pin 19) and is prescaled in the PLL IC based on the divided
ratio (N-data). The PLL IC detects the out-of-step phase
using the reference frequency and outputs it from pin 13.
The output signal is passed through the loop filter (Q31,
Q32) and is then applied to the 1st VCO circuit as the lock
voltage.
4-2-2 CONVERTER PLL CIRCUIT
(RF AND VCO UNITS)
An oscillated signal from the converter VCO is applied to the
buffer and RF amplifiers (Q862, Q863). The amplified signal
passes through the bandpass filter (VCO unit; C972–C979,
C981, C982, L921–L924), and is then amplified at the RF
amplifier (VCO unit; Q864) and LO amplifier (RF unit;
Q874). The amplified signal is applied to the converter PLL
IC (RF unit; IC15, pin 1) and is prescaled in the converter
PLL IC based on the divided ratio (N-data). The converter
PLL IC detects the out-of-step phase using the reference
frequency and outputs it from pin 10. The output signal is
passed through the loop filter (RF unit; C956–C958, R945,
R946) and is then applied to the converter VCO circuit as
the lock voltage.
4-2-3 REFERENCE OSCILLATOR CIRCUIT
(VCO UNIT)
The reference oscillator circuit (X1, IC3) generates a 12.8
MHz reference frequency which is stabilized within the tem-
perature range –10˚C (+14˚F) to +60˚C (+140˚F). The refer-
ence frequency is applied to the PLL IC (IC3, pin 16) and the
signal is output from pin 17, and is then applied to the con-
verter PLL IC (RF unit; IC15, pin 6) and FM IF IC (RF unit;
IC2, pin 2).
4-2-4 1ST VCO CIRCUIT (VCO UNIT)
The oscillated signal is applied to the buffer amplifier (IC4).
The amplified signal is applied to the 1st mixer circuit (RF
unit; IC1, pin 3) via the RX LO swtich circuit (RF unit;
D63–D68) and doubler circuit (RF unit; Q25).
The 1st VCO circuit (Q22, Q23, D62) oscillates 240.6
MHz–359.9475 MHz (Low) and 348.1 MHz–520.0475 MHz
(High) respectively by switching the SHIFT switch (Q21,
D61).
A portion of the signal from IC4 is amplified at the buffer
amplifier (Q25) and is then fed back to the PLL IC (IC3, pin
19) as the comparison signal.
4-2-5 2ND VCO CIRCUIT (VCO UNIT)
The 2nd LO circuit generates the 2nd LO frequencies, and
the signals are applied to the 2nd mixer circuit.
The 2nd VCO circuit (Q34, D202) oscillates 183.1–297.1
MHz signal. The oscillated signal is applied to the 2nd mixer
(RF unit; IC10, pin 3), and is then mixed with the 1st IF sig-
nal.
An oscillated signal from the 2nd VCO is applied to the
buffer amplifier (Q853). The amplified signal passes through
the low-pass filter (C154, C250–C252, L69), and is applied
to the PLL IC (IC3, pin 2), and is then output from pin 8.
4-2-6 CONVERTER VCO CIRCUIT (VCO UNIT)
The converter LO circuit generates the converter LO fre-
quencies, and the signals are applied to the converter mixer
circuit.
The converter VCO circuit (Q816, D913) oscillates
645.5–675.5 MHz signal. The oscillated signal is applied to
the buffer amplifier (Q862), and is then amplified at the RF
amplifier (Q863) to double the oscillating frequency. The
1291–1351 MHz signal is applied to the RF amplifier (Q864)
via the bandpass filter (C972–C979, C981, C982,
L921–L924). The amplified signal is applied to the converter
mixer (RF unit; IC13, pin 3), and is then mixed with the
above 1150 MHz RF signal.
An oscillated signal from the converter VCO is applied to the
LO amplifier (RF unit; Q874). The amplified signal is applied
to the converter PLL IC (RF unit; IC15, pin 1).

4-3 FM-TV CIRCUIT

4-3-1 FM-TV CIRCUIT (FM-TV UNIT)
([OTH-2] only includes this unit)
The 426.05 MHz 1st IF signal from the 1st mixer (RF unit;
IC1, pin 6) passes through the IF switching diode (D1) via
the J6 on the RF unit. The signal is passed through the
bandpass filter (FI1) to suppress unwanted signal, and then
applied to the IF amplifier (IC1, pin 4). The amplified signal
is applied to the FM-TV detector IC (IC2, pins 24 and 25).
The FM-TV detector IC contains the AGC amplifier, loop
amplifier, video amplifier, etc. The video and audio signals
are output from the FM-TV detector separately.
• VIDEO SIGNAL
The detected video signal from the FM-TV IC (IC1) is ampli-
fied at the buffer amplifier (Q21), and then applied to the
amplifier (IC21, pin 1 and 8). The amplified signal is applied
to the video selector IC (IC22, pin 1 and 3) to obtain 6 dB
amplification. The amplified signal is output from the video
selector IC (pin 7), and is then applied to the buffer amplifi-
er (RF unit; Q855) via the "VIDEO" signal. The amplified sig-
nal is applied to the TFT LCD circuit on the LOGIC unit.
• AUDIO SIGNAL
The oscillator (Q51, C53–C55, C57, D51, D52) oscillates
14–28 MHz signal.The detected audio signal from the FM-
TV IC (IC1) is amplified at the buffer amplifier, and is then
applied to the mixer (Q41). The signal is mixed with oscillat-
ed 14–28 MHz signal to produce the 13.25 MHz IF signal at
the mixer. The IF signal passes through the band switching
diode (RF unit; D72) and bandpass filter (RF unit; FI4). The
filtered signal is amplified at the 2nd IF amplifier (RF unit;
Q41), and is applied to the FM IF IC (RF unit; IC2, pin 16).
The detected signal is applied to the AF circuit (LOGIC unit)
for speaker, and applied to the A/V OUT jack (RF unit; J3)
via the RF amplifier (Q71).
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