Vertex Standard VX-1210, Руководство по обслуживанию

Страница: 19 / 76

19
Receive Signal Path
Incoming RF signal from the ANT jack is delivered to J3005
on the PA Unit, and passes through the TX/RX relay RL3013 to
the low-pass filter which consists of the coils L3016 & L3017
and capacitors C3050, C3051, & C3052 which cut-off frequency
is 30 MHz.
The RF signal is then applied to J1001 on the MAIN Unit,
and passed through the limitter circuit consist of D1001 , D1002 ,
D1003 , and D1004 (all 1SS244 ) to prevent the distortion from
the high RF input and one of eight band-pass filters which strip
away unwanted signals to the RF amplifier
Q1001 and Q1002
(both
2SK520-K41
).
The amplified RF signal is applied to the double balanced
mixer D1009 ( HSB88WS ) where the RF signal is mixed with
1st local signal delivered from buffer Q1005 ( 2SC2954 ), re-
sulting in a 47.055 MHz 1st IF signal.
The 47.055 MHz 1st IF signal is fed through the monolithic
crystal filter XF1001 (
47M15AU
) which strip away unwanted
mixer products, and then the 1st IF signal is applied to the 2nd
mixer
Q1006 ( 3SK151GR ), where it is mixed with the 36.355
MHz 2nd local signal delivered from buffer amplifier Q2038
( 2SC2714Y ) on the Control Unit, resulting in a 10.7 MHz 2nd
IF signal.
The 10.7 MHz 2nd IF signal is fed through the Noise Blanker
Gate D1014 & D1015 (both
1SS302
) and 2nd IF filter XF1002
( 10M2.4D ) to the 2nd IF amplifier Q1007 , Q1008 , & Q1009
(all 3SK151GR ).
A portion of the 2nd IF signal is amplified by Q1011 & Q1012
(both 3SK151GR ), and then detected (with twofold voltage
amplitude) by diode D1016 (
HSM198S
). This detected output
controls the gain of above-mentioned FET by an average AGC
voltage responsible for AGC amplifier
Q1013 (
2SC2812
). Also,
noise pulse contained in the detected output is amplified by the
Q1014 ( 2SC2812 ) to be utilized for controlling Noise Blanker
Gate D1014 & D1015 .
In SSB, CW and FSK modes, the amplified 2nd IF signal
from Q1009 is applied to the product detector diode D1024 &
D1025 (both
HSM198S
).
In AM mode, the amplified 2nd IF signal from Q1009 is fed
through the buffer amplifier Q1015 ( 2SC2812 ) and AM detec-
tor diodes D1021 & D1022 (both HSM198S ).
The audio signal from the selected detector is amplified by
AF preamplifier Q1023 (
M5218AFP
). The audio signal is then
fed through the AF mute gate Q1025 (
TC4S66F
) and front panel
AF potentiometer VR4001 , then back to audio amplifier Q1027
( TDA2822D ) and Q1058 ( TDA7235 ).
A portion of the output of AM detector diodes D1021 &
D1022 is amplified by AGC amplifier Q1016 (
2SC2812
). The
amplified DC voltage is fed through the buffer amplifier Q1018
(
2SC2812
) to the RF amplifier Q1002 and also the amplified
DC voltage is fed to the 2nd gates of the IF amplifiers Q1007 ,
Q1008 , & Q1009 , to reduce their gain when strong signals are
present in the receiver passband.
Circuit Description
When pulse type noise is received, a sample of the 2nd IF
signal from Q1006 is amplified by Q1011 & Q1012 (both
3SK151GR ) before application to pulse detector D1016
(
HSM198S
). The resulting DC pulse switches noise blanker gate
controller Q1014 ( 2SC2812 ), which interrupts the 2nd IF sig-
nal at noise blanker gate D1014 & D1015 during the length of
the noise pulse.
The DC voltage from the pulse detector is also amplified by
Q1013 ( 2SC2812 ) and fed back to 2nd gates of the AGC ampli-
fier Q1011 & Q1012 as noise blanker AGC.
Transmit Signal Path
The speech audio from the microphone is delivered to J8001
on the MIC-CONN Unit, then applied to the J2002 on the CNTL
Unit.
The speech audio is amplified by Q2046 ( NJM4558V ) and
Q2050 (
M5218AFP
), then passed though the MIC gain potenti-
ometer VR1001, and further amplified by Q1043 (
2SC2812
)
before application to balanced modulator D1036 (
HSB88WS
).
The modulator also receives 10.7 MHz carrier signal from buffer
amplifier
Q1022 ( 2SC2812 ).
The modulated signal is delivered to the crystal filter XF1002
where is stripped unwanted sideband. The resulting 10.7 MHz
single sideband signal is buffered by
Q1045 (
2SK302GR
) and
then applied to single balanced mixer Q1046 (
3SK151GR
)
which receives 36.355 MHz local signal from buffer amplifier
Q2038 on the CNTL Unit. In AM mode, the single balanced
mixer Q1046 also receivers 10.7 MHz carrier signal from buffer
amplifier Q1022 to resulting the double sideband (AM) signal.
The resulting the 47.055 MHz IF signal is fed through the
monolithic crystal filter XF1001 which strip away unwanted
mixer products, and then amplified by Q1048 (
3SK151GR
).
The amplified IF signal is delivered to double balanced mixer
D1009 , where it is mixed with the PLL local signal from the
buffer amplifier Q1005 ( 2SC2954 ).
The resulting the RF signal at the transmit frequency is fed
through the TX amplifier Q1049 (
2SC2714Y
) and buffer am-
plifier Q1050 (
2SC3357
), and then filtered by one of eight
bandpass filters to suppress out-of-band mixer products. The RF
signal is then amplified by
Q1051 ( 2SC2954 ) and delivered to
PA Unit.
On the PA Unit, the low-level RF signal from the Main Unit
is amplified by pre-drive Q3501 (
2SC2166
), push-pull driver
Q3502/Q3503 (both
2SC2166
), and then push-pull final am-
plifier Q3504/Q3505 (both 2SC3133 ), which provides approxi-
mately 20 watts RF output power.
The RF output from the final amplifier is fed through the one
of six low-pass filters, sampling directional coupler T3001, and
TX/RX relay RL3014 before delivery to the antenna jack.
The sampling directional coupler senses forward and reverse
power output, which is rectified by D3001/D3005 & D3002/
D3006 (all 1SS106 ) respectively for return to the ALC and SWR
sensing circuitry on the Main Unit. The DC voltages derived
from forward and reverse power are applied in combination to