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1. Receiver System
1-1. F
-
rF
ront
end
ampliFier
Incoming RF signal from the antenna passes through the
Low-pass filter, antenna switching diode Dx513, Dx514 (both
1SS390), and the RF attenuator Qx508 (SKY12338), and then
removed undesired frequencies by the varactor tuned band-
pass filter Dx515 and Dx516 (both 1SV325).
The filtered RF signal is amplified by Qx518 (2SC5006)
and then passes through another varactor tuned band-pass
filter Dx520 and Dx521 (both 1SV325) to remove the unde-
sired frequencies, and then applied to the 1st mixer Qx523
(3SK293).
1-2. F
m
irst
ixer
The RF signal is mixed with the 1st local signal between
186.85 and 224.85 MHz in the 1st mixer Qx523 (3SK293), to
produce 50.85 MHz 1st IF signal.
The 1st local signal is generated by the VCO, which consists
of Qx506 (2SC5006), varactor diodes Dx502 (1SV279),
Dx504 (xSV282), Dx507 (1SV279), and Dx508 (1SV282).
The 1st local signal is supplied to the 1st mixer Qx523
(3SK293) through the buffer amplifier Qx510 (2SC5005) and
amplifier Qx524 (2SC5006).
1-3. iF a
& d
mpliFier
The 1st IF signal is applied to the monolithic crystal filter
XFx501 to strip away all but the desired signal, and then sup-
plied to the custom IC Qx522 (RODINIA) through the buffer
amplifier Qx526 (2SC5226). The custom IC Qx522 (RODIN-
IA) converts the 1st IF signal into the Base Band signal.
The Base Band signal from the custom IC Qx522 (RODINIA)
is applied to another custom IC Qx306 (OMAP), which is de-
modulated by the Digital Signal Processor.
1-4. a
a
udio
mpliFier
The demodulated signal from the custom IC Qx306 (OMAP)
is applied to another custom IC Qx017 (CPCAP). The custom
IC Qx017 (CPCAP) adjusts the audio volume level, and then
amplifies the audio signal up to 500 mW. The output signal
from the custom IC Qx017 (CPCAP) is applied to the audio
speaker.
EVX-531 VHF Service Manual
emodulator
Circuit Description
2. Transmitter System
2-1. miC a
& m
mpliFier
The speech signal from internal microphone MCx001 or ex-
ternal microphone Jx003 is supplied to the custom IC Qx017
(CPCAP), which is amplified the speech signal.
The amplified speech signal from the custom IC Qx017
(CPCAP) is supplied to another custom IC Qx306 (OMAP),
which process the speech signal by the Digital Signal Proces-
sor.
The processed speech signal from the custom IC Qx306
(OMAP) is supplied to the modulator section of the custom
IC Qx522 (RODINIA), which modulates the speech signal
into the FM or digital signal.
2-2. d
& F
a
rive
inal
mpliFier
The modulated signal from the custom IC Qx522 (RODINIA)
is buffered by Qx520 (2SK3077) and amplified by the driver
amplifier Qx519 (RQA0004PXDQS), and then is applied to
the final amplifier Qx513 (RQA0011DNS), which is ampli-
fied up to 5 watts output power.
The transmit signal then passes through the antenna switch
Dx512 (RN124S) and is low pass filtered to suppress away
harmonic spurious radiation before delivery to the antenna.
2-3. a
t
utomatiC
ransmit
The current detector Qx528-1 (AD8566ARM) detects the
current of the final amplifier Qx513 (RQA0011DNS) and the
driver amplifier Qx519 (RQA0004PXDQS), and converts the
current difference to the voltage difference.
The output from the current detector Qx528-1 (AD8566ARM)
is compared with the reference voltage and amplified by the
power control amplifier Qx528-2 (AD8566ARM).
The output from the power control amplifier Qx528-2
(AD8566ARM) controls the gate bias of the driver amplifier
Qx519 (RQA0004PXDQS) and the final amplifier Qx513
(RQA0011DNS).
The reference voltage changes into four values (Transmit
Power High and Low) controlled by custom IC Qx522 (RO-
DINIA).
Parts reference number is as follows
MAIN Unit (w/o Option Connector): 1000 - 1999
MAIN-3 Unit (w/ Option Connector): 3000 - 3999
odulator
s
tages
p
C
ower
ontrol
8
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