Vertex Standard TRANSCEIVER VX-1700 - Manual (Page 7)

7
Circuit Description
Receive Signal Path
Incoming RF signal from the ANT jack is delivered
to the PA Unit, and passes through the TX/RX relay
RL2009 to J2006.
The RF signal is then applied to J1001 on the MAIN
Unit, and passed through the limiter circuit consist-
ing of D1006, D1007, D1008, and D1009 (all RLS245)
to prevent distortion from high RF signal input, and
is fed to one of eight band-pass filters which strip
away unwanted signals prior to delivery of the in-
coming signal to the RF amplifiers, Q1022 and Q1024
(both 2SK520-K41).
The amplified RF signal passes through a low-pass
filter to the doubly-balanced mixer D1032
(HSB88WS), where the RF signal is mixed with the
1st local signal delivered from buffer amplifier
Q1029 (2SC2954), resulting in a 45.274 MHz 1st IF
signal.
The 45.274 MHz 1st IF signal is fed through mono-
lithic crystal filter XF1001, which strips away un-
wanted mixer products, and is amplified by 1st IF
amplifier Q1050 (3SK151GR); the 1st IF signal is
then applied to the 2nd mixer Q1052 (RF2713),
where it is mixed with the 45.25 MHz 2nd local sig-
nal which is divided from 90.5 MHz reference sig-
nal delivered from buffer amplifier Q1075
(2SC2714Y), resulting in a 24 kHz 2nd IF signal.
The 24 kHz 2nd IF signal is fed through buffer am-
plifiers Q1030 and Q1041 (both UPC4572G2) to the
A/D converter Q1071 (AK4528A), then delivered to
the DSP IC Q1035 (UPD77115), where the 24 kHz
2nd IF signal is demodulated in accordance with the
mode selection data from the main CPU Q1018
(HD64F2134). The demodulated signal is delivered
to the D/A converter Q1081 (AK4550VT) which con-
verts the demodulated signal to audio.
The audio signal from the D/A converter Q1081
(AK4550VT) is fed through a low-pass filter at Q1036
(UPC4572G), which eliminates high-pitched noise
on the audio signal, and is fed to the AF mute gate
Q1092 (2SJ125D), then applied to the audio ampli-
fier Q1055 (TDA2003H). The amplified audio signal
is delivered to J3001 on the PANEL Unit, then pass-
es through the speaker switch RL3001/Q3006
(DTC143ZE) to the internal or external speaker.
The DSP IC Q1035 (UPD77115) outputs AGC data
which is proportionate to the received signal
strength to the main CPU Q1018 (HD64F2134). The
main CPU Q1018 (HD64F2134), in turn, outputs a
DC voltage in accordance with the received signal
strength. This DC voltage is fed through buffer am-
plifier Q1039 (LM2904PW) to RF amplifiers Q1022
& Q1024 (both 2SK520) and gate 2 of IF amplifier
Q1050 (3SK151GR), to reduce their gains when
strong signals are present in the receiver passband.
Transmit Signal Path
The speech audio from the microphone is delivered
to J6001 on the MIC Unit, then applied to J1005 on
the MAIN Unit.
The speech audio is amplified by Q1032-1
(UPC4572G2), then passed though the clipper,
D1044 (MC2850), and further amplified by Q1032-2
(UPC4572G2).
The amplified speech audio is fed through the A/D
converter Q1081 (AK4550VT), then delivered to the
DSP IC Q1035 (UPD77115), where the speech au-
dio is modulated in the 24 kHz TX 1st IF signal in
accordance with the mode selection data from the
main CPU, Q1018 (HD64F2134).
The modulated signal is fed through the D/A con-
verter Q1071 (AK4528A) and buffer amplifier Q1034
(UPC4572G2) to the mixer Q1054 (RF2713) where
the 24 kHz TX 1st IF signal is mixed with 1st local
signal delivered from buffer amplifier Q1075
(2SC2714Y), resulting in a 45.274 MHz IF signal.
The resulting 45.274 MHz IF signal is buffered by
Q1049 (3SK151GR), then delivered to the monolith-
ic crystal filter XF1001, which strips away unwant-
ed mixer products, and then is amplified by Q1043
(3SK151GR). The amplified IF signal is delivered
to doubly-balanced mixer D1032 (HSB88WS),
where it is mixed with the PLL local signal from the
buffer amplifier, Q1029 (2SC2954).
The resulting the RF signal at the transmit frequen-
cy is fed through a low-pass filter circuit, and then
is amplified by Q1026 (2SC2714Y) and buffer am-
plifier Q1025 (2SC3357), and then filtered by one
of eight band-pass filters to suppress out-of-band
responses. The RF signal is then amplified by Q1001
(2SC2954) and delivered to the PA Unit.