Kenwood TS-480HX Service Manual page 6

TS-480HX/480SAT
■ From receiving 1st mixer to the second IF fre-
quency (10.695MHz)
The output signal sent from the RF BPF passes through
the image filter and is converted to the first IF frequency
(73.095MHz) at the first receiving mixer (Q156, 157, 160,
161). The receiving first mixer has a circuit having quadruple
JFETs (Q156, 157, 160, 161). This same type of circuit is
used in high-class transceivers. Therefore, this transceiver
has the same or higher dynamic characteristics as high-class
transceivers.
Two MCF (XF151) with 2-poles are used in the next stage.
This transceiver reduces proximity spurious components of
ANT1
10.695MHz
RX 2nd IF
to TX-RX (A/2)
■ 10.695MHz IF filter circuit (Filter section (X57-663
B/2) of the TX-RX unit)
The TX-RX unit (X57-663 A/2) comprises the receiver cir-
cuit, the PLL circuit, the transmitter circuit (from AF to the
first IF: 10.695MHz), the AF DSP, and the control circuit.
The second IF signal (10.695 MHz) input into CN501 of the
TX-RX unit (X57-663 A/2) enters CN901 of the filter section
(X57-663 B/2). This unit has the 10.695MHz IF filter and the
IF amplifier. It is possible to remove the unit to mount a op-
tional IF filter (two pieces) and TCXO (SO-3).
The second IF signal (10.695MHz) input from CN901 is
amplified at the second receiver IF amplifier (Q901). The sec-
ond receiver IF amplifier operates as a gate of the noise
blanker. Q902 and Q901 turn OFF while blanking. Q901 am-
plifies the transmit signal.
The output signal sent from Q901 passes through the
10.695MHz IF filter and is amplified at the IF amplifier (Q971),
then returns to the TX-RX unit (X57-663 A/2) from CN971.
Table 4 shows the path of the 10.695MHz IF filter mode.
You can mount two IF filters from the following optional IF
filter types:
6
CIRCUIT DESCRIPTION
ANT2 Filter unit (C/3)
ANT section
Except 200W
RX
TX
AT
TX
signal
D256
1st IF AMP
RX 2nd Mixer
Q255
LO2 AMP
LO2
62.4MHz
Fig. 3 From antenna to the second IF frequency (10.695MHz)
the transmit signal by passing the narrow-band MCF. It also
reduces spurious components of the receive signal.
TP1 (CN152) and TP2 (CN252) adjust MCF. The signal
passed through the MCF is amplified at the first IF amplifier
(Q253) and converted to the second IF frequency (10.695
MHz) at the second receiving mixer (D256). The receiving
second mixer is the passive type mixer using diodes and the
transmit signal passes through it when performing transmis-
sion.
The second IF signal (10.695MHz) is sent from CN254 of
the RF unit (X44-327) to CN501 of the TX-RX unit (X57-663 A/
2) through a co-axial cable.
RF unit
ATT RF BPF
–12dB/
30kHz~
–20dB 60MHz
Through
PRE AMP OFF
Q253
MCF
XF151
73.095MHz
AGC LO1
73.125~133.095MHz
SSB NARROW: 1.8kHz, CW: 500Hz, and CW NARROW:
270Hz.
The option filter is automatically selected by the resis-
tance, which is set in the option filter. Therefore, you do not
need to select the filter using menu or a switch.
Filter
Through (R943, 945)
XF931
XF932
Option filter 1
Option filter 2
*1: The bandwidth of the mounted IF filter is applied.
*2: The mode changes corresponding to the mounted IF filter.
The CW filter is available in SSB mode with the selection is in the
menu.
Table 4 IF filter selection
Q153,154
PRE AMP
Q156,157,160,161
RX 1st Mixer
Q159
LO1 AMP
Bandwidth RX
Through FM Not used
6kHz AM AM
2.4kHz SSB/CW/FSK SSB/CW/FSK
/AM NAR /FM
*1 *2 Not used
*1 *2 Not used
TX