Vertex evx-534 - Circuit Description: Receiver and Transmitter Systems; Receiver System; Transmitter System

EVX-534/-539 VHF Service Manual 8
1. Receiver System
1-1. Front-end rF ampliFier
Incoming RF signal from the antenna passes through the
Low-pass lter, antenna switching diode D1513, D1514 (both
1SS390), and the RF attenuator Q1508 (SKY12338), and then
removed undesired frequencies by the varactor tuned band-
pass lter D1515 and D1517 (both 1SV325).
The filtered RF signal is amplified by Q1518 (2SC5006)
and then passes through another varactor tuned band-pass
lter D1520 and D1521 (both 1SV325) to remove the unde-
sired frequencies, and then applied to the 1st mixer Q1523
(3SK293).
1-2. First mixer
The RF signal is mixed with the 1st local signal between
186.85 and 224.85 MHz in the 1st mixer Q1523 (3SK293), to
produce 50.85 MHz 1st IF signal.
The 1st local signal is generated by the VCO, which consists
of Q1506 (2SC5006), varactor diodes D1502 (1SV279),
D1504 (1SV282), D1507 (1SV279), and D1508 (1SV282).
The 1st local signal is supplied to the 1st mixer Q1523
(3SK293) through the buffer amplier Q1510 (2SC5006) and
amplier Q1524 (2SC5005).
1-3. iF ampliFier & demodulator
The 1st IF signal is applied to the monolithic crystal filter
XF1501 to strip away all but the desired signal, and then sup-
plied to the custom IC Q1522 (RODINIA) through the buffer
amplier Q1526 (2SC5226). The custom IC Q1522 (RODIN-
IA) converts the 1st IF signal into the Base Band signal.
The Base Band signal from the custom IC Q1522 (RODINIA)
is applied to another custom IC Q1306 (OMAP), which is de-
modulated by the Digital Signal Processor.
1-4. audio ampliFier
The demodulated signal from the custom IC Q1306 (OMAP)
is applied to another custom IC Q1017 (CPCAP). The custom
IC Q1017 (CPCAP) adjusts the audio volume level. The ad-
justed audio is amplied by Q1003 (TDA2822L). As a result,
the audio signal provides up to 700 mW (@16-ohm, BTL) for
the internal speaker, or up to 350 mW (@4-ohm, OTL) for
the external speaker.
2. Transmitter System
2-1. miC ampliFier & modulator
The speech signal from internal microphone MC1001 or ex-
ternal microphone J1003 is supplied to the custom IC Q1017
(CPCAP), which is amplied the speech signal.
The amplified speech signal from the custom IC Q1017
(CPCAP) is supplied to another custom IC Q1306 (OMAP),
which process the speech signal by the Digital Signal Proces-
sor.
The processed speech signal from the custom IC Q1306
(OMAP) is supplied to the modulator section of the custom
IC Q1522 (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 Q1522 (RODINIA)
is buffered by Q1520 (2SK3077) and amplied by the driver
amplier Q1519 (RQA0004PXDQS), and then is applied to
the final amplifier Q1513 (RQA0011DNS), which is ampli-
ed up to 5 watts output power.
The transmit signal then passes through the antenna switch
D1512 (RN142S) 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 Q1528-1 (AD8566ARM) detects the
current of the nal amplier Q1513 (RQA0011DNS) and the
driver amplier Q1519 (RQA0004PXDQS), and converts the
current difference to the voltage difference.
The output from the current detector Q1528-1 (AD8566ARM)
is compared with the reference voltage and amplied by the
power control amplier Q1528-2 (AD8566ARM).
The output from the power control amplifier Q1528-2
(AD8566ARM) controls the gate bias of the driver amplier
Q1519 (RQA0004PXDQS) and the final amplifier Q1513
(RQA0011DNS).
The reference voltage changes into four values (Transmit
Power High and Low) controlled by custom IC Q1522 (RO-
DINIA).
Circuit Description