EVX-531 UHF Service Manual 9
1. Receiver System
1-1. Front-end rF ampliFier
Incoming RF signal from the antenna passes through the
Low-pass lter, antenna switching diode Dx513, Dx514 (both
1SS390), and the RF attenuator Qx508 (SKY12338), and then
removed undesired frequencies by the varactor tuned band-
pass lter Dx515 and Dx516 (both 1SV331).
The filtered RF signal is amplified by Qx518 (2SC5006)
and then passes through another varactor tuned band-pass
lter Dx520 and Dx521 (both 1SV331) to remove the unde-
sired frequencies, and then applied to the 1st mixer Qx523
(3SK293).
1-2. First mixer
The RF signal is mixed with the 1st local signal between
352.15 and 419.15 MHz (Type “G6”) or 399.15 and 469.15
MHz (Type “G7”) in the 1st mixer Qx523 (3SK293), to pro-
duce 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 (Type “G6”: 1SV282, Type “G7”: 1SV279), Dx507
(1SV279), and Dx508 (Type “G6”: 1SV282, Type “G7”:
1SV279). The 1st local signal is supplied to the 1st mixer
Qx523 (3SK293) through the buffer amplifier Qx510
(2SC5005) and amplier Qx524 (2SC5005).
1-3. iF ampliFier & demodulator
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
amplier 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. audio ampliFier
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
amplies the audio signal up to 500 mW. The output signal
from the custom IC Qx017 (CPCAP) is applied to the audio
speaker.
2. Transmitter System
2-1. miC ampliFier & modulator
The speech signal from internal microphone MCx001 or ex-
ternal microphone Jx003 is supplied to the custom IC Qx017
(CPCAP), which is amplied 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. drive & Final ampliFier stages
The modulated signal from the custom IC Qx522 (RODINIA)
is buffered by Qx520 (2SC5227) and amplied by the driver
amplier Qx519 (RQA0004PXDQS), and then is applied to
the final amplifier Qx513 (RQA0011DNS), which is ampli-
ed 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. automatiC transmit power Control
The current detector Qx528-1 (AD8566ARM) detects the
current of the nal amplier Qx519 (RQA0011DNS) and the
driver amplier Qx515 (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 amplied by the
power control amplier Qx528-2 (AD8566ARM).
The output from the power control amplifier Qx528-2
(AD8566ARM) controls the gate bias of the driver amplier
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).
Circuit Description
Parts reference number is as follows
MAIN Unit (Type “G7”, w/o Option Connector): 1000 - 1999
MAIN-2 Unit (Type “G6”, w/o Option Connector): 2000 - 2999
MAIN-3 Unit (Type “G6” & “G7”, w/ Option Connector): 3000 - 3999
To Next Page
Loading...
Need help?
General
