Icom IC-730 Maintenance Manual page 9

shunts the RF signals to ground. This grounds the anodes
of 020 and 021, and turns them OFF. Thus the noise
pulse is not fed to the following circuits.
The signal which passes the NB gate circuit is then fed to
the 2nd mixer consisting of 01 - 04 diode OBM.
The 2nd local oscillator consisting of
Q9
and X1 oscillates
at 30.71901MHz . 30.720MHz with 10Hz steps. 019
varactor diode provides this frequency variation. A control
voltage generated in the LOGIC unit and ~C-amplified in
the MAIN unit is applied to 019. The oscillation frequency
can be adjusted by L 1 and the voltage applied to 019. The
2nd local oscillator signal is about +2dBm and is fed to the
L6 center tap in the 2nd mixer circuit to convert the 1st
IF signal to 2nd IF (9.0115MHz) signal.
elf
O----------------ill~--~~
416
J3
88~----------~~
J4
eWH
0-.......
_.+----;-0
csw O-+-......
f-..,
J3
Df
R8~----------------------~
The voltage CSW is fed to the filter selection pins consisting
of P3, J7 and JS, through pin 1 of J4 and 017. P3 is con-
nected to J7 when the set has been shipped. When the
optional SSB crystal filter (this provides PBT function) is
installed, P3 should be connected to JS.
The voltage CWN is fed to the filter selection pin~ consisting
of P2, J5 and J6, through pin 2 of J4 and O1S. P2 is con-
nected to J5 when the set has been shipped. When the
optional CW crystal filter is installed, P2 should be con·
nected to J6.
When any optional filters are not installed (the filter se-
lection pins are original connections), the bases of 04 and
05 are not applied with any bias voltages, so 04 and 05
are turned OFF and both emitters are OV. Thus 09 and
013 are turned OFF and 06 is turned ON, and 010 and
011 are turned ON and FI1 is selected in any modes.
When the optional SSB crystal filter is installed and P3 is
connected to JS, 05 is turned ON and RSV is applied to
07 and OS, and 07 and OS are turned ON. Thus the SSB
3-2
The 2nd I F signal is fed to FI1 monolithic crystal filter
installed as standard. When optional SSB crystal filter,
FL-30, and/or CW crystal filter, FL-45 is installed, the
suitable crystal filter is selected by the MODE switch.
FI1 has 3kohm input/output impedance, so LS and L9
work as step-up and step-down matching transformers
respectively. FI1 has lower insertion loss than other
optional filters, so R15 and R2S are inserted as an at-
tenuator. L9 is tuned by 012 varactor diode, which gives
more isolation when other filters are selected. The filtered
2nd IF signal is then fed to the MAIN unit through P1.
Filter selection is made by voltages CWN (applied in CW-N
mode) and pSW (applied in other modes) from the MODE
switch through J4.
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DIO
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crystal filter is selected. At the same time, RSV is applied
to the base of 06 through 013 and turns OFF 06, thus FI1
is isolated from the circuit.
When the optional CW crystal filter is installed and P2 is
connected to J6, 04 is turned ON and RSV is applied to
05 and 023, and 05 and 023 are turned ON. Thus the
CW crystal filter is selected. At the same time, RSV is
applied to the base of 06 through 09 and turns OFF 06,
thus FI1 is isolated from the circuit the same as when SSB
crystal filter is installed.
06 is turned ON when the optional CW filter is selected,
and it shunts to ground the optional SSB filter input
terminal to prevent signal leakage in the pass band of the
SSB filter.
These optional filters are selected only when the set is in
the receive mode.
3-1-3 MAIN UNIT
The receive signal from the 2nd I F unit P1 is fed to J16 on
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