Receiver Circuits; Transmitter Circuits - Icom IC-FR5000 Service Manual Addendum

SECTION 5

5-1 RECEIVER CIRCUITS

RF BPF CIRCUITS
RX signals from the RX antenna connector (J11) are passed
through the 1st stage of BPF (D28, 29, 31, 32, L44, 47) then
amplified by the RF AMP (Q36). The amplified RX signals
are passed through the 2nd stage of BPF (D28, 29, 31,
32, L44, 47) to remove unwanted signals for good image
response then applied to the 1st mixer (L27, 32, D62).
Being mixed with 1st LO signals from the RX VCO, the RX
signals are converted into the 46.35 MHz 1st IF signal.
The 1st and 2nd stage of the BPFs are tuned to the pass
band frequency by tracking voltage "T1" and "T2" from
the DAC (IC17). The gain of low noise RF AMP (Q36) is
controlled by the AGC circuit (Q39, D27) according to the
RX signal strength.
IF FILTER/IF AMP CIRCUITS
The 1st IF signal from the 1st mixer (L27, 32, D62) is
amplifi ed by the buffer AMP (Q63, 64, 71) and 1st stage of
IF AMP (Q19) then fi ltered by crystal fi lter (FI3 or FI4), and
then applied to the IF IC (IC5).
The crystal fi lters (FI3 or FI4) are switched by the "NWC1"
signal from the CPU (IC20) according to the RX mode; Wide
(Middle), Narrow or Digital.
<ANALOG RX>
Being mixed with the 2nd LO, the 1st IF signal is converted
into the 450 kHz 2nd IF signal. The 2nd IF signal is passed
through the external ceramic filter (FI1 or FI2), then FM-
demodulated by the internal quadrature detector with
discriminator (X3). The demodulated AF signals are
amplifi ed by the AF AMP (IC36), and applied to the LINER
CODEC (IC8). The AF signals are converted into the
digital audio signal then processed by the DSP (IC12) then
recovered to the analog audio signals.
The ceramic filter (FI1 or FI2) is switched by the "NWC2"
signal from the CPU (IC20) according to the RX mode; Wide
(Middle), Narrow or Digital.
<DIGITAL RX>
The 450 kHz 2nd IF signal is amplifi ed by IC7 then applied
to the DSP (IC12) via ADC (IC9), and digital-demodulated.
The processed digital signal is converted into the analog
audio signal by the LINEAR CODEC (IC8).
AF AMPLIFIER CIRCUITS
The AF signals from the LINEAR CODEC are amplifi ed by
the AF AMP (IC36) and level-adjusted by DAC (IC2), then
applied to IC28 via IC29 to be power-amplifi ed.
SIGNALING (DECODE)
The Continious Tone (CTCSS/DTCS), Single Tone (5-Tone/
DTMF/CW_ID) signals in the demodulated AF signals are
decoded in the DSP (IC8).
CIRCUIT DESCRIPTION

5-2 TRANSMITTER CIRCUITS

MODULATION CIRCUITS
The demodulated signals are applied to the MIC AMP (IC25).
The amplified Demodulated signals are passed through the
SW IC (IC35) which selects the source of Demodulated signals
from J5 (from MIC) and from D-SUB connector (DEXM).
The Demodulated signals from the SW IC are amplifi ed by
an AMP (IC1) then applied to the LINEAR CODEC IC (IC8)
where the Demodulated signals are converted in to the
digital audio signals.
The converted digital audio signals are processed (pre-
emphasis, limit, etc.) by the DSP (IC12), then recovered to
the analog audio signals by LINER CODEC IC (IC8). The AF
signals are amplifi ed by IC1 and level-adjusted by Electronic
VR (IC2), then applied to the TX VCO and TCXO (X1) as the
modulation signals.
SIGNALING (ENCODE)
The Continious Tone (CTCSS/DTCS), Single Tone (5-Tone/
DTMF/CW_ID) signals are encoded, and mixed with
Demodulated signals in the DSP (IC12).
YGR/PA CIRCUITS
The output signals from TX VCOs are amplified to the level
required for the PA module by pre-AMPs (Q37, 38), then
amplifi ed by the PA module (IC22) to obtain TX output power. The
power-amplifi ed TX signal is passed through the ANT SW (D44)
and LPF (for harmonics removal) then applied to the TX antenna.
APC CIRCUIT
D45, D48 and D49 detect the TX power, and the detected
voltage is applied to the IC23 in APC circuit. Comparing the
detected voltage which is in proportion to the TX power and
power setting voltage as the reference voltage, IC23 adjusts
the bias voltage of PA module (pin 2: VGG terminal) and pre-
AMP (Q38) to control the TX power.
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