Icom IC-PCR1500 Service Manual page 13

• 1300–3300 MHz*
The 1300–3300 MHz signals from the antenna are applied to
the down converter circuit where those signals are converted
into the lower frequencies.
<DOWN CONVERTER>
D42
LPF
To the RF circuits
(350–1300 MHz)
The received signals are applied to the buffer amplifi er (Q11)
via the band switch (D15). The buffer-amplifi ed signals are
applied to the RF amplifi er (IC5, pin 1) via HPF (L35, L38,
C89, C92, C93, C100, C103). The amplified signals are
output from pin 4, and applied to the mixer (IC6, pin 1) and
down-converted. The down converted signals are output
from pin 6, then applied to the RF circuits via LPF (L66,
C190, C193) and band switch (D42). The LO frequencies
and convered frequencies are shown as below.
RX frequency LO frequency
1300–1700 MHz 1001 MHz
1700–2300 MHz 1001 MHz
2300–2700 MHz 2002 MHz
2700–3300 MHz 2002 MHz
4-1-2 1st IF CIRCUITS
The 1st IF circuits contain a 1st mixer, 1st IF amplifi er and
1st IF fi lter. The 1st IF mixer converts the received signals
into a fi xed frequency of the 1st Intermediate Frequency (IF)
signal. The converted 1st IF signal is filtered at the 1st IF
fi lters, then amplifi ed at the 1st IF amplifi er.
The converted signals from the RF circuits are applied to the
1st IF mixer (IC14, pins 4, 5) and converted into the 266.7
MHz 1st IF signal by being mixed with the 1st LO (Local
Oscillator) signals from the 1st-VCO's.
The converted IF signal is passed through the 1st IF filter
(FI1) to fi lter out the unwanted signals, then applied to the 1st
IF amplifi er (Q44). The amplifi ed 1st IF signal is then applied
to the 2nd mixer (IC19, pin 4) via attenuator (R263, R264).
4-1-3 2nd IF CIRCUITS (MAIN UNIT)
The 2nd IF circuits contain the 2st mixer, 2nd IF amplifier
and the 2nd IF fi lters.
The 1st IF signal from the 1st IF circuits is converted into
the 10.7 MHz 2nd IF signal by being mixed with the 2nd LO
signals from the 2nd-VCO.
The converted 2nd IF signal is applied to the 2nd IF amplifi er
(Q60). The amplifi ed 2nd IF signal is passed through the 2nd
IF fi lter to fi lter out the unwanted signals.
LO signals from VCO (Q19, D43)
IC5 Q11
D15
RF Buff
HPF
amp. amp.
From the
antenna
Convered frequency
350–700 MHz
700–1300 MHz
350–700 MHz
700–1300 MHz
In FM or AM mode, the 2nd IF signal is passed through the
FI5 (band width=50 kHz) via mode switches (D66, D70),
In WFM mode, the 2nd IF signal is passed through the FI6
(band width=230 kHz) via mode switches (D67, D71).
The fi ltered 2nd IF signal is applied to the 2nd IF amplifi er
(Q66). The amplifi ed 2nd IF signals are then applied to the
3rd IF and demodulation circuits.
4-1-4 NOISE BLANKER CIRCUIT
The noise blanker (NB) circuit reduces pulse type noises
in the received signals. When the received signals contain
pulse type noise components, the NB circuit reduces the
noisy AF signals by cutting off the 2nd IF line.
In AM, SSB or CW mode and the NB function is activated, a
portion of the 2nd IF signal from the band switch (D70, D71)
is amplifi ed at NB amplifi er (Q68) and applied to the IF IC
(IC16, pin 2).
When the 2nd IF signal contains a pulse noise, the RSSI
signal corresponding to the pulse noise level is output from pin
17. The output RSSI signal turns Q49 ON and Q65 turns OFF,
thus the Q66 is inactivated and the 2nd IF signal is cut off.
4-1-5 3rd IF AND DEMODULATOR CIRCUITS
(MAIN-A/B UNIT)
The 2nd IF signal is converted into the 3rd IF signal (except
WFM mode) and demodulated in the IF IC. The IF IC
contains a 3rd mixer, limiter amplifi er, quadrature detector,
etc. in its package.
In FM mode, the 2nd IF signal from the 2nd IF amplifier
(Q66) is applied to the IF IC (IC24, pin 16) via mode switch
(D78) and IF gain control circuit (D97).
The applied 2nd IF signal is converted into the 3rd IF signal
by being mixed with 3rd LO signal from the TCXO (X1), at
the 3rd mixer in the IF IC (IC24). The converted 3rd IF signal
is output from pin 3 and applied to the 3rd IF amplifi er (Q62).
The amplifi ed 3rd IF signal is passed through one of the 3rd
IF fi lter according to the receiving mode.
The filtered 3rd IF signal is applied to the limiter amplifier
(IC24, pin 5), then applied to the demodulator circuit (pin 10,
X2) and FM-demodulated. The FM-demodulated AF signals
are output from pin 9, then applied to the AF circuits.
In AM and CW mode, the 3rd IF signal from the 3rd IF fi lter
is applied to the 3rd IF amplifier (Q61). The amplified 3rd
IF is applied to the AM demodulator circuit (D75) via the
buffer amplifi er (Q63). The AM-demodulated AF signals are
applied to AF circuits via the AF selector (IC27, pins 3, 4).
In SSB mode, the 3rd IF signal from the buffer amplifier
(Q63) are applied to the AF mixer (IC23, pin 6) and
converted into the AF signal by being mixed with the 447.3–
452.7 kHz BFO signal from the DDS circuits. The converted
audio signals are applied to the AF selector (IC27, pin 1)
after being fi ltered at the HPF (IC31, pins 1, 4).
In WFM mode, the 2nd IF signal is applied to the IF IC
(IC16, pin 2) via the 2nd IF amplifi er (Q66) and mode switch
(D90, D91). The 2nd IF signal is amplified at the limiter
amplifier, then applied to the demodulator circuit (pins 11,
12, X2) and FM-demodulated. The FM-demodulated AF
signals are output from pin 8, then applied to the AF circuits
via the AF selector (IC27, pins 8, 9).
4 - 2
*MAIN-A UNIT only